RC step response 2 of 3 solve

WEBVTT
Kind: captions
Language: en

00:00:00.896 --> 00:00:02.905
- [Voiceover] In the last
video on step response,

00:00:02.905 --> 00:00:04.911
we set up the differential equation

00:00:04.911 --> 00:00:07.711
that describes our
circuit, and we found that

00:00:07.711 --> 00:00:09.460
it was a non-homogeneous equation,

00:00:09.460 --> 00:00:10.737
and now we're gonna follow through

00:00:10.737 --> 00:00:13.281
on the strategy of solving it with a

00:00:13.281 --> 00:00:16.614
forced response plus a natural response.

00:00:17.502 --> 00:00:19.500
So here's two copies of our circuit,

00:00:19.500 --> 00:00:21.430
and we're gonna, on the top one here,

00:00:21.430 --> 00:00:25.358
we're gonna solve for
the natural response,

00:00:25.358 --> 00:00:27.519
and on the bottom one, we'll use that one

00:00:27.519 --> 00:00:29.519
for the forced response.

00:00:31.286 --> 00:00:33.406
Alright, let's go to work on the natural.

00:00:33.406 --> 00:00:35.376
Now, to do a natural response,

00:00:35.376 --> 00:00:38.802
what we do is we set
the initial conditions

00:00:38.802 --> 00:00:41.498
to whatever they were
for the original circuit,

00:00:41.498 --> 00:00:43.525
so that involves some q

00:00:43.525 --> 00:00:47.325
and a v zero, a v naught on the capacitor.

00:00:47.325 --> 00:00:49.915
So let's just draw in
quick, let's draw in our q.

00:00:49.915 --> 00:00:54.239
There's some q here, that'll
be a plus or minus v naught

00:00:54.239 --> 00:00:55.771
on the capacitor.

00:00:55.771 --> 00:00:59.050
Now the other thing we
do, is for the inputs,

00:00:59.050 --> 00:01:02.802
we set the inputs to zero
to do the natural response.

00:01:02.802 --> 00:01:04.821
And how you do that,

00:01:04.821 --> 00:01:06.850
our input here is a voltage source,

00:01:06.850 --> 00:01:08.595
and we're gonna suppress
the voltage source,

00:01:08.595 --> 00:01:10.833
that's how we do it with super position.

00:01:10.833 --> 00:01:12.356
When you suppress a voltage source,

00:01:12.356 --> 00:01:14.516
what you do is you set
the voltage to zero.

00:01:14.516 --> 00:01:17.240
And that means that's the same as creating

00:01:17.240 --> 00:01:18.780
a short circuit for this.

00:01:18.780 --> 00:01:20.686
So, for the natural response

00:01:20.686 --> 00:01:22.886
we're gonna take out

00:01:22.886 --> 00:01:24.569
our voltage source

00:01:24.569 --> 00:01:28.486
and replace it with a
short circuit, like this.

00:01:31.034 --> 00:01:33.940
So, this circuit now is identical

00:01:33.940 --> 00:01:37.155
to the circuit that we used
for the natural response.

00:01:37.155 --> 00:01:39.383
So, if you haven't seen that video

00:01:39.383 --> 00:01:41.521
on how to solve for the natural response,

00:01:41.521 --> 00:01:44.097
this would be a good
time to go look at that.

00:01:44.097 --> 00:01:45.528
What I'm gonna do now is just write down

00:01:45.528 --> 00:01:49.061
the answer from that, this
will be plus or minus,

00:01:49.061 --> 00:01:51.228
we'll call this v natural,

00:01:53.200 --> 00:01:55.188
and that equals

00:01:55.188 --> 00:01:56.355
some k natural

00:01:57.900 --> 00:01:59.733
times e to the minus t

00:02:00.665 --> 00:02:01.627
over

00:02:01.627 --> 00:02:02.460
r c.

00:02:04.183 --> 00:02:07.793
This is the natural
response of an r c circuit,

00:02:07.793 --> 00:02:12.020
so I'll put a square around
that so we can remember it.

00:02:12.020 --> 00:02:13.833
And I've left the constant in here,

00:02:13.833 --> 00:02:18.677
and we'll work out what this
constant is a little bit later.

00:02:18.677 --> 00:02:20.190
Okay, so now let's move on

00:02:20.190 --> 00:02:22.672
and do the forced
response for this circuit.

00:02:22.672 --> 00:02:24.681
And for the forced response,

00:02:24.681 --> 00:02:28.848
we remember the initial
conditions are set to zero.

00:02:30.507 --> 00:02:33.474
So that means that q equals zero here,

00:02:33.474 --> 00:02:35.285
and that means that

00:02:35.285 --> 00:02:36.118
initial v

00:02:37.205 --> 00:02:38.112
is zero.

00:02:38.112 --> 00:02:40.112
I'll just write in zero.

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So that's what it means to set

00:02:44.268 --> 00:02:46.196
the initial conditions to zero.

00:02:46.196 --> 00:02:47.363
And the inputs

00:02:49.549 --> 00:02:50.929
are equal to,

00:02:50.929 --> 00:02:52.220
we use to inputs this time,

00:02:52.220 --> 00:02:54.387
the input is equal to v s.

00:02:55.498 --> 00:02:58.433
And in particular, the
input is equal to v s,

00:02:58.433 --> 00:03:00.512
we're gonna solve the forced response

00:03:00.512 --> 00:03:03.755
after time is equal to
zero, so that means that

00:03:03.755 --> 00:03:04.755
the input is

00:03:05.613 --> 00:03:06.793
v s,

00:03:06.793 --> 00:03:07.793
capital v s.

00:03:08.906 --> 00:03:11.220
And as a reminder, what
we're trying to solve here

00:03:11.220 --> 00:03:15.459
is the differential equation
from the previous screen,

00:03:15.459 --> 00:03:16.967
and that is

00:03:16.967 --> 00:03:17.824
c

00:03:17.824 --> 00:03:18.657
times d v

00:03:19.801 --> 00:03:20.634
d t,

00:03:21.471 --> 00:03:23.638
I'll put a forced in here,

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plus one over r,

00:03:27.688 --> 00:03:28.855
times v forced

00:03:29.797 --> 00:03:31.214
equals one over r

00:03:32.740 --> 00:03:33.573
times v

00:03:33.573 --> 00:03:35.197
s,

00:03:35.197 --> 00:03:37.024
and I can plug in capital v s here

00:03:37.024 --> 00:03:38.109
because we're trying to solve this

00:03:38.109 --> 00:03:41.101
for this initial condition.

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So this is our differential equation

00:03:43.448 --> 00:03:45.228
for the forced response,

00:03:45.228 --> 00:03:47.354
and we're gonna take a strategy here

00:03:47.354 --> 00:03:49.395
that's like we did with
the natural response,

00:03:49.395 --> 00:03:52.660
is we're gonna guess at an answer for v f,

00:03:52.660 --> 00:03:55.230
and then plug it into this
differential equation,

00:03:55.230 --> 00:03:57.692
this non-homogeneous
differential equation,

00:03:57.692 --> 00:04:00.497
and we're gonna see if it works.

00:04:00.497 --> 00:04:02.734
And a good guess here
is to guess something

00:04:02.734 --> 00:04:04.901
that looks like the input.

00:04:06.792 --> 00:04:08.337
So a good guess is gonna be some function

00:04:08.337 --> 00:04:10.004
that looks like v s.

00:04:11.402 --> 00:04:13.813
And v s looks like what?

00:04:13.813 --> 00:04:17.040
V s looks like, over here,
v s looks like a constant.

00:04:17.040 --> 00:04:19.601
So we're gonna make a guess here that

00:04:19.601 --> 00:04:23.351
the forced response
looks like some constant,

00:04:24.437 --> 00:04:26.104
we'll call that k f.

00:04:27.985 --> 00:04:31.056
The way we test our guess is
to plug it back into here.

00:04:31.056 --> 00:04:33.859
Plug it back into the
differential equation.

00:04:33.859 --> 00:04:35.595
So I'm gonna do that, alright so we get

00:04:35.595 --> 00:04:36.428
c times

00:04:38.574 --> 00:04:41.117
the derivative of k f,

00:04:41.117 --> 00:04:42.867
with respect to time,

00:04:43.953 --> 00:04:45.286
plus one over r,

00:04:47.153 --> 00:04:47.986
k sub f,

00:04:48.879 --> 00:04:50.321
equals

00:04:50.321 --> 00:04:51.154
one over r

00:04:52.365 --> 00:04:53.198
times v s.

00:04:55.631 --> 00:04:59.798
Alright, now here's the interesting
thing that happens next.

00:05:01.081 --> 00:05:04.401
What's the derivative of a
constant with respect to time?

00:05:04.401 --> 00:05:05.234
That's

00:05:07.898 --> 00:05:08.951
That goes to zero.

00:05:08.951 --> 00:05:11.821
So this first leading term here
of our differential equation

00:05:11.821 --> 00:05:12.904
goes to zero,

00:05:14.116 --> 00:05:15.538
and now I'm left with

00:05:15.538 --> 00:05:17.205
k f times one over r

00:05:18.144 --> 00:05:21.105
equals v s times one over r.

00:05:21.105 --> 00:05:24.224
So that makes k f equal to v s.

00:05:24.224 --> 00:05:26.104
So I'll tuck this in here,

00:05:26.104 --> 00:05:27.771
our forced response,

00:05:28.998 --> 00:05:30.079
v f

00:05:30.079 --> 00:05:30.912
equals

00:05:31.949 --> 00:05:32.782
v s.

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So now I have our

00:05:41.381 --> 00:05:44.309
natural response right here,

00:05:44.309 --> 00:05:46.310
and in this square we
have our forced response,

00:05:46.310 --> 00:05:49.893
the forced response is
just a constant v s.

00:05:53.294 --> 00:05:56.015
So now we're ready to come
up with our total response,

00:05:56.015 --> 00:05:58.688
and we'll call that v capital t,

00:05:58.688 --> 00:06:02.701
the total response is equal
to the natural response

00:06:02.701 --> 00:06:03.534
plus

00:06:04.803 --> 00:06:06.332
the forced response.

00:06:06.332 --> 00:06:10.260
So now we're using our
principal of super position.

00:06:10.260 --> 00:06:11.093
Okay, v t

00:06:12.157 --> 00:06:13.310
equals

00:06:13.310 --> 00:06:14.143
k

00:06:15.052 --> 00:06:16.438
some constant times e

00:06:16.438 --> 00:06:18.012
to the minus t

00:06:18.012 --> 00:06:18.845
over r c.

00:06:19.696 --> 00:06:22.241
And let's add the forced response,

00:06:22.241 --> 00:06:24.195
and the forced response is right here,

00:06:24.195 --> 00:06:25.028
it's v s,

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and we're getting close,

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the only thing we have left is
to figure out this value now,

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we have to figure out the gain factor

00:06:34.535 --> 00:06:38.286
in front of the exponential
term of the natural response.

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Now the way we go after that,

00:06:39.806 --> 00:06:42.200
is we would know this
if we knew what v s is,

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and we do, it's called v s.

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If we knew v t at some time,

00:06:47.596 --> 00:06:49.243
we could plug in two values here.

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We could plug in a v t and a t,

00:06:51.245 --> 00:06:55.185
and one of the most
convenient times to know this,

00:06:55.185 --> 00:06:57.352
if we set t equal to zero,

00:06:59.867 --> 00:07:04.314
and we know that the total
at time equals zero is what?

00:07:04.314 --> 00:07:06.684
It's basically, let me roll
it up here a little bit,

00:07:06.684 --> 00:07:09.555
let's go backwards a little bit.

00:07:09.555 --> 00:07:11.572
Let me go back here and
use this diagram again,

00:07:11.572 --> 00:07:13.830
this was the forced response,

00:07:13.830 --> 00:07:16.184
so we're not gonna use that right now.

00:07:16.184 --> 00:07:19.079
We're gonna use, this
is now the total circuit

00:07:19.079 --> 00:07:21.731
all assembled together,
and we have to figure out

00:07:21.731 --> 00:07:23.879
what is the actual initial charge on here,

00:07:23.879 --> 00:07:27.055
and if we recall, the
initial charge on here

00:07:27.055 --> 00:07:28.066
was v

00:07:28.066 --> 00:07:29.211
naught,

00:07:29.211 --> 00:07:31.894
it was this value here,

00:07:31.894 --> 00:07:33.809
just before time equals zero,

00:07:33.809 --> 00:07:36.573
this was the value of the
voltage on that capacitor.

00:07:36.573 --> 00:07:40.466
So I can fill that in here, v naught.

00:07:40.466 --> 00:07:43.635
Alright, let's go back
to our total solution

00:07:43.635 --> 00:07:45.108
and plug in these two values,

00:07:45.108 --> 00:07:47.988
time is zero and v t equals v naught.

00:07:47.988 --> 00:07:49.488
So that looks like

00:07:50.572 --> 00:07:52.147
v naught

00:07:52.147 --> 00:07:52.980
equals

00:07:55.340 --> 00:07:58.840
natural constant times e to the minus zero

00:08:00.091 --> 00:08:00.924
over r c

00:08:02.103 --> 00:08:02.936
plus v s.

00:08:05.026 --> 00:08:07.224
And let's solve for k n

00:08:07.224 --> 00:08:08.057
k n

00:08:09.456 --> 00:08:10.564
equals,

00:08:10.564 --> 00:08:12.731
this term is e to the zero

00:08:13.618 --> 00:08:14.451
is one,

00:08:15.448 --> 00:08:17.389
so this term goes to one,

00:08:17.389 --> 00:08:20.139
that says that it's k n plus v s,

00:08:21.514 --> 00:08:22.728
is this side,

00:08:22.728 --> 00:08:25.029
and I can write down here

00:08:25.029 --> 00:08:25.862
v naught

00:08:27.395 --> 00:08:28.660
minus

00:08:28.660 --> 00:08:29.493
v s.

00:08:30.852 --> 00:08:33.578
So now I've solved for k,

00:08:33.578 --> 00:08:35.073
and we can finish our total response,

00:08:35.073 --> 00:08:38.997
we can say the total
response is v t equals

00:08:38.997 --> 00:08:40.646
k sub n,

00:08:40.646 --> 00:08:42.979
which is v naught minus v s,

00:08:45.285 --> 00:08:47.340
e to the minus t

00:08:47.340 --> 00:08:48.173
over r c

00:08:50.262 --> 00:08:51.095
and

00:08:51.095 --> 00:08:51.928
plus v s.

00:08:56.620 --> 00:08:59.120
And that is the total response

00:09:02.457 --> 00:09:03.935
of our circuit,

00:09:03.935 --> 00:09:05.120
and we saw that in two steps,

00:09:05.120 --> 00:09:08.047
first we did the natural
and then we did the forced

00:09:08.047 --> 00:09:12.219
and we added them together and
worked out the last constant,

00:09:12.219 --> 00:09:16.386
whatever the constant was,
and there's our answer.

00:09:17.899 --> 00:09:20.698
So in the next video we'll
do an explicit example

00:09:20.698 --> 00:09:23.142
with values for r and c in the step

00:09:23.142 --> 00:09:26.470
and we'll see what it actually looks like.


RC step response 3 of 3 example

WEBVTT
Kind: captions
Language: en

00:00:01.200 --> 00:00:03.080
- [Voiceover] In the
last video, we worked out

00:00:03.080 --> 00:00:05.280
the step response of an RC circuit,

00:00:05.280 --> 00:00:07.820
and now we're gonna
look at a real example.

00:00:08.680 --> 00:00:11.400
So, this is our answer,
this is the step response,

00:00:11.400 --> 00:00:14.700
the total response to our
circuit, to a step input.

00:00:15.560 --> 00:00:16.960
And what does this look like?

00:00:16.960 --> 00:00:18.480
Well, I'm gonna move down a little bit.

00:00:18.480 --> 00:00:21.860
We'll make up a circuit and
we'll do a real example here.

00:00:42.500 --> 00:00:44.240
Let's say we do a step,

00:00:44.240 --> 00:00:48.340
and the step goes from .2 volts

00:00:49.940 --> 00:00:54.040
up to, say 1.1 volts.

00:00:55.120 --> 00:00:58.840
And let's let R equal one K, ohm.

00:00:58.840 --> 00:01:01.120
K, ohm.

00:01:01.120 --> 00:01:05.220
And let the capacitor
equal four microfarads.

00:01:08.380 --> 00:01:11.500
So now let's plug these values
over here into our solution

00:01:11.500 --> 00:01:12.680
and see what we get.

00:01:12.680 --> 00:01:14.860
Now, first I'm gonna work out RC.

00:01:14.860 --> 00:01:18.660
RC is equal to one K, ohm

00:01:18.660 --> 00:01:21.980
times four microfarads.

00:01:21.980 --> 00:01:23.520
And what does that equal?

00:01:23.520 --> 00:01:25.340
K is plus three.

00:01:26.580 --> 00:01:29.240
And micro is minus six.

00:01:29.240 --> 00:01:32.000
So one times four is four.

00:01:32.000 --> 00:01:34.860
And plus three minus six is times

00:01:34.860 --> 00:01:37.160
10 to the minus three.

00:01:39.500 --> 00:01:41.040
And that is in seconds,

00:01:41.040 --> 00:01:45.680
so that's equal to four milliseconds.

00:01:45.680 --> 00:01:48.016
Now, let's plug the rest
of our values in here.

00:01:48.016 --> 00:01:49.500
V of T.

00:01:51.400 --> 00:01:53.760
The total response, or the step response

00:01:53.760 --> 00:01:56.880
equals v naught, .2,

00:01:59.260 --> 00:02:03.360
minus V, S, that's the step voltage, 1.1,

00:02:05.840 --> 00:02:10.240
times e to the minus t

00:02:10.240 --> 00:02:13.380
over four milliseconds

00:02:15.100 --> 00:02:17.336
plus V, S.

00:02:17.336 --> 00:02:19.700
V, S is 1.1.

00:02:23.200 --> 00:02:25.180
So I went ahead and I plotted this

00:02:25.180 --> 00:02:28.460
using a computer, and we'll
see how close this comes

00:02:28.460 --> 00:02:30.040
to what we sketched earlier.

00:02:36.760 --> 00:02:38.760
So here's V, T.

00:02:41.040 --> 00:02:43.140
Or, the step response, the total response

00:02:43.140 --> 00:02:46.884
of our RC network to a step voltage.

00:02:46.884 --> 00:02:49.980
The step voltage is here in rose color.

00:02:51.560 --> 00:02:55.024
And it goes from .2 volts up to,

00:02:55.024 --> 00:02:56.654
ooh, I got it wrong.

00:02:56.654 --> 00:02:59.940
1.2 volts, let's change
that to the right number.

00:03:01.060 --> 00:03:04.560
1.2, 1.2.

00:03:05.600 --> 00:03:06.880
And this is what it looks like.

00:03:06.880 --> 00:03:08.980
And if you go back and
compare this to what we saw,

00:03:08.980 --> 00:03:10.580
what we sketched at the beginning,

00:03:10.580 --> 00:03:12.080
it'll look pretty similar.

00:03:12.080 --> 00:03:16.040
So, the output voltage, the
voltage on the capacitor here,

00:03:20.180 --> 00:03:23.046
starts at V naught, which is .2,

00:03:23.046 --> 00:03:27.560
it ends up at V, S, which
is 1.2 in this case,

00:03:27.560 --> 00:03:29.500
and that's the forced response up here.

00:03:29.500 --> 00:03:33.240
And in between, it did that
smooth exponential curve.

00:03:34.860 --> 00:03:37.640
That's what the step response
of an RC circuit looks like.


RC step response 1 of 3 setup

WEBVTT
Kind: captions
Language: en

00:00:00.160 --> 00:00:02.781
- [Voiceover] In the last video
we looked at this RC circuit

00:00:02.781 --> 00:00:06.510
and we gave it a step
input with a step source,

00:00:06.510 --> 00:00:08.576
a step from V nought up to V S,

00:00:08.576 --> 00:00:12.214
with a sharp change right
here at T equals zero.

00:00:12.214 --> 00:00:14.188
And we sort of took an intuitive guess

00:00:14.188 --> 00:00:17.118
at what this voltage looks like here.

00:00:17.118 --> 00:00:18.368
That's V and T.

00:00:19.329 --> 00:00:20.563
And in this video we're going to develop

00:00:20.563 --> 00:00:22.503
a precise expression for what happens here

00:00:22.503 --> 00:00:25.184
to this voltage across the capacitor.

00:00:25.184 --> 00:00:27.750
And as we said, this is a
very very common circuit,

00:00:27.750 --> 00:00:30.036
there's millions and millions
of these types of circuits

00:00:30.036 --> 00:00:32.908
inside every computer, so it really pays

00:00:32.908 --> 00:00:35.729
to understand this one quite well.

00:00:35.729 --> 00:00:37.721
Because this is a function of time,

00:00:37.721 --> 00:00:39.385
because we have a function of time here,

00:00:39.385 --> 00:00:42.021
this is going to end up
needing some techniques

00:00:42.021 --> 00:00:45.325
from calculus to really
figure out properly.

00:00:45.325 --> 00:00:47.239
So this is going to be a place

00:00:47.239 --> 00:00:51.060
where our calculus skills
are really necessary.

00:00:51.060 --> 00:00:53.352
And I'm also going to
assume that you've listened

00:00:53.352 --> 00:00:56.042
to the video on RC natural response

00:00:56.042 --> 00:00:57.619
where we worked out the expression

00:00:57.619 --> 00:01:00.944
for the natural response when
there was no voltage here,

00:01:00.944 --> 00:01:03.252
where this was zero.

00:01:03.252 --> 00:01:05.702
The natural response looks like

00:01:05.702 --> 00:01:06.869
V equals V not

00:01:08.702 --> 00:01:10.785
E to the minus T over RC.

00:01:11.729 --> 00:01:14.854
And there's a video on Khan
Academy about natural response

00:01:14.854 --> 00:01:19.022
and there's also an
article you can read too.

00:01:19.022 --> 00:01:21.678
So let's get back here,
let's analyze this fourmulae.

00:01:21.678 --> 00:01:24.175
And one of the things we can do is, well,

00:01:24.175 --> 00:01:28.418
first thing we always do is
we always label the quantities

00:01:28.418 --> 00:01:31.436
that we want in here, and
I'll put, there's the current,

00:01:31.436 --> 00:01:34.603
and here we'll call this voltage of R,

00:01:36.082 --> 00:01:39.606
and if I've used a
lowercase letter V or I,

00:01:39.606 --> 00:01:41.971
that means that quantity
is changing with time

00:01:41.971 --> 00:01:45.242
and if I use a big, a
capital letter V here,

00:01:45.242 --> 00:01:47.934
that means that those values
don't change with time.

00:01:47.934 --> 00:01:49.851
So that's why notation.

00:01:50.742 --> 00:01:53.144
And when we analyze the
circuit, a good thing to do

00:01:53.144 --> 00:01:56.298
is just to look at what
are the compound equations

00:01:56.298 --> 00:01:57.449
for this thing.

00:01:57.449 --> 00:02:00.431
So let's talk about Ohm's
Law for this resistor here.

00:02:00.431 --> 00:02:01.764
We know that V R

00:02:03.225 --> 00:02:04.558
equals I times R

00:02:06.949 --> 00:02:08.611
Or another way that we can write that is

00:02:08.611 --> 00:02:09.444
I equals

00:02:10.963 --> 00:02:11.796
V R over R

00:02:15.008 --> 00:02:16.447
So the other expression that I could write

00:02:16.447 --> 00:02:18.808
for the capacitor is the
capacitor of I equation

00:02:18.808 --> 00:02:20.233
which is I

00:02:20.233 --> 00:02:21.400
equals C DV DT

00:02:25.715 --> 00:02:27.877
and this means the slope of the voltage

00:02:27.877 --> 00:02:30.016
or the rate of change of the voltage

00:02:30.016 --> 00:02:32.821
times C is equal to the current.

00:02:32.821 --> 00:02:34.848
Alright, so far so good.

00:02:34.848 --> 00:02:36.004
I have one I.

00:02:36.004 --> 00:02:38.022
There's actually only
one I in this circuit.

00:02:38.022 --> 00:02:42.052
So this I here is equal to this one here,

00:02:42.052 --> 00:02:45.126
that's a good relationship for us to know.

00:02:45.126 --> 00:02:46.980
Oh and we also have two
different V variables,

00:02:46.980 --> 00:02:49.658
we have regular V that's
across the capacitor

00:02:49.658 --> 00:02:51.543
and we have V sub R.

00:02:51.543 --> 00:02:53.545
So let me see if I can write V sub R

00:02:53.545 --> 00:02:54.712
in terms of V.

00:02:55.927 --> 00:02:58.015
And one thing I can
tell from this circuit,

00:02:58.015 --> 00:02:59.848
this point right here,

00:03:01.237 --> 00:03:02.237
this is V S.

00:03:03.584 --> 00:03:05.213
This point right here

00:03:05.213 --> 00:03:06.213
this is V C.

00:03:07.457 --> 00:03:08.957
So I can write V R

00:03:10.941 --> 00:03:11.774
equals V S

00:03:14.362 --> 00:03:15.195
minus V C.

00:03:18.171 --> 00:03:20.051
Alright, that's going
to be useful. Alright.

00:03:20.051 --> 00:03:21.439
So now what I'm going to do is I'm going

00:03:21.439 --> 00:03:23.661
to set these two I's equal to each other

00:03:23.661 --> 00:03:25.308
and at the same time I'll

00:03:25.308 --> 00:03:28.620
plug in this expression V S minus V C

00:03:28.620 --> 00:03:31.599
for V R up here. It will go in right here.

00:03:31.599 --> 00:03:32.849
So we can write

00:03:34.239 --> 00:03:35.406
C DV DT equals

00:03:42.584 --> 00:03:44.251
one over R times V R

00:03:46.150 --> 00:03:47.900
V R is V S minus V C.

00:03:51.675 --> 00:03:55.092
I shouldn't write V C, I'll just write V.

00:03:56.852 --> 00:03:57.813
I'll take that out there

00:03:57.813 --> 00:04:01.226
because we don't need that subscript.

00:04:01.226 --> 00:04:05.226
And multiply through by
one over R et on, we get

00:04:07.033 --> 00:04:07.866
C DV DT

00:04:10.086 --> 00:04:11.836
equals one over R V S

00:04:15.418 --> 00:04:16.918
minus one over R V

00:04:20.594 --> 00:04:22.165
and we'll get

00:04:22.165 --> 00:04:22.998
C DV DT

00:04:27.121 --> 00:04:28.454
minus one over R

00:04:30.366 --> 00:04:31.199
times V

00:04:32.304 --> 00:04:33.137
equals V S

00:04:38.950 --> 00:04:42.111
Alright so now we have, this
is our differential equation.

00:04:42.111 --> 00:04:43.304
It's a differential equation

00:04:43.304 --> 00:04:44.940
because it has derivatives in it.

00:04:44.940 --> 00:04:47.009
In particular this is called

00:04:47.009 --> 00:04:48.426
a non-homogeneous

00:04:56.383 --> 00:04:59.465
ordinary differential equation.

00:04:59.465 --> 00:05:02.277
It's ordinary because
there's a first derivative,

00:05:02.277 --> 00:05:04.927
the first derivative
has a power of one here,

00:05:04.927 --> 00:05:06.309
that's the ordinary.

00:05:06.309 --> 00:05:08.979
It's a differential equation
because it has a derivative

00:05:08.979 --> 00:05:10.999
and it's called non-homogeneous

00:05:10.999 --> 00:05:14.499
because this side over here, this is not V

00:05:15.682 --> 00:05:17.368
or a derivative of V.

00:05:17.368 --> 00:05:19.702
So this equation is sort of mixed up,

00:05:19.702 --> 00:05:21.452
it's non-homogeneous.

00:05:22.767 --> 00:05:24.938
When we did the natural response analysis,

00:05:24.938 --> 00:05:27.293
this term right here was zero

00:05:27.293 --> 00:05:31.460
in that equation, so we were
able to solve this rapidly.

00:05:32.729 --> 00:05:34.750
So we're going to develop
a new strategy here

00:05:34.750 --> 00:05:36.338
for solving this kind of equation

00:05:36.338 --> 00:05:39.336
this kind of non-homogeneous ODE.

00:05:39.336 --> 00:05:41.033
So this equation is a little tricky

00:05:41.033 --> 00:05:43.956
to solve because this
is not zero over here.

00:05:43.956 --> 00:05:45.894
We have a mixture of things going on here.

00:05:45.894 --> 00:05:47.508
This side of the equation represents

00:05:47.508 --> 00:05:48.679
the forcing function.

00:05:48.679 --> 00:05:51.610
This is what the circuit
is being driven to

00:05:51.610 --> 00:05:54.679
by that step response
input voltage source.

00:05:54.679 --> 00:05:57.020
And this side here we're
going to get tied up

00:05:57.020 --> 00:05:58.739
with the initial conditions

00:05:58.739 --> 00:06:00.335
that that capacitor has,

00:06:00.335 --> 00:06:02.457
so there's sort of two
things going on here,

00:06:02.457 --> 00:06:04.135
that make this a little more complicated

00:06:04.135 --> 00:06:05.559
than usual to solve.

00:06:05.559 --> 00:06:09.726
And so what our strategy is,
we take on a strategy here.

00:06:13.858 --> 00:06:16.749
We break the problem down into two pieces.

00:06:16.749 --> 00:06:17.990
This is always what engineers do

00:06:17.990 --> 00:06:19.047
when they're faced with something

00:06:19.047 --> 00:06:20.949
that is a little
complicated, is you try to

00:06:20.949 --> 00:06:22.794
break it into bits and pieces.

00:06:22.794 --> 00:06:25.061
So what we're going to
do is, our strategy is

00:06:25.061 --> 00:06:29.061
to figure out what we
call the natural response.

00:06:34.158 --> 00:06:36.309
And we're going to figure
out something called

00:06:36.309 --> 00:06:37.976
the forced response.

00:06:43.040 --> 00:06:44.508
And then we're going to add those together

00:06:44.508 --> 00:06:46.218
with a plus sign, and that's going

00:06:46.218 --> 00:06:49.341
to be equal to what we
call the total response.

00:06:49.341 --> 00:06:52.674
So this is what the circuit really does.

00:06:55.266 --> 00:06:56.353
Alright so we got two new words here.

00:06:56.353 --> 00:06:58.753
One is the forced response,
and one's the total response.

00:06:58.753 --> 00:07:02.282
And if we remember before,
the natural response

00:07:02.282 --> 00:07:05.079
was what the circuit did
when nothing was forcing it.

00:07:05.079 --> 00:07:07.483
We just put in some initial
energy, some charge,

00:07:07.483 --> 00:07:09.014
and let the circuit sort of sag

00:07:09.014 --> 00:07:10.873
toward wherever it was going.

00:07:10.873 --> 00:07:12.653
That's the natural response.

00:07:12.653 --> 00:07:14.695
The forced response is going to be

00:07:14.695 --> 00:07:17.982
what the input source
forces the circuit to do.

00:07:17.982 --> 00:07:20.200
And when we take those two
things and add them together

00:07:20.200 --> 00:07:22.853
we'll get what the circuit
is going to do altogether.

00:07:22.853 --> 00:07:27.020
And this is another good
application of super position.

00:07:33.881 --> 00:07:36.367
We're going to take two
things that the circuit does

00:07:36.367 --> 00:07:38.192
and analyze them separately

00:07:38.192 --> 00:07:40.645
and then add them
together, superimpose them,

00:07:40.645 --> 00:07:42.812
to get the total response.

00:07:43.869 --> 00:07:45.892
So they way we do this, the strategy is

00:07:45.892 --> 00:07:47.975
for the natural response,

00:07:49.707 --> 00:07:53.340
basically we take for
the initial conditions,

00:07:53.340 --> 00:07:55.801
that's the charge on the capacitor,

00:07:55.801 --> 00:07:56.796
we'll take whatever we get.

00:07:56.796 --> 00:08:00.963
We'll take the initial Q
and the initial V W, V not.

00:08:03.357 --> 00:08:05.940
And when we look at the inputs,

00:08:07.583 --> 00:08:10.226
we'll set the inputs to zero.

00:08:10.226 --> 00:08:12.097
So that's how we analyze,
that's the conditions

00:08:12.097 --> 00:08:13.934
for the natural response.

00:08:13.934 --> 00:08:16.926
And when we take the forced response

00:08:16.926 --> 00:08:18.093
we do the opposite, what we do is

00:08:18.093 --> 00:08:20.146
we set the initial conditions to zero,

00:08:20.146 --> 00:08:21.890
simplify the circuit down

00:08:21.890 --> 00:08:24.039
and we use the inputs that
are actually applying.

00:08:24.039 --> 00:08:27.084
In this case, it was V of S.

00:08:27.084 --> 00:08:29.938
And then you get the total response,

00:08:29.938 --> 00:08:32.291
we add those together, with a plus sign.

00:08:32.291 --> 00:08:34.874
So then for the total response,

00:08:37.618 --> 00:08:41.785
you get the initial conditions,
which is Q and V not,

00:08:42.749 --> 00:08:46.057
and you get V S, all together.

00:08:46.057 --> 00:08:47.503
So that's our strategy.

00:08:47.503 --> 00:08:50.185
And by turning it into
two simpler problems,

00:08:50.185 --> 00:08:52.723
basically we make this
differential equation

00:08:52.723 --> 00:08:54.942
a little bit simpler to solve two times

00:08:54.942 --> 00:08:58.634
than trying to solve it
all together at once.

00:08:58.634 --> 00:09:01.193
We'll stop here now and in the next video,

00:09:01.193 --> 00:09:02.826
we'll follow through on the strategy

00:09:02.826 --> 00:09:06.993
of combining the forced response
with the natural response.


Conceptual overview of light dependent reactions

WEBVTT
Kind: captions
Language: en

00:00:00.311 --> 00:00:01.839
- [Voiceover] We've
seen in previous videos

00:00:01.839 --> 00:00:04.300
that photosynthesis can be broken down

00:00:04.300 --> 00:00:07.900
into the light-dependent
reactions and the Calvin cycle.

00:00:07.900 --> 00:00:09.617
And the light-dependent reactions is

00:00:09.617 --> 00:00:12.313
where we take light as an
input along with water,

00:00:12.313 --> 00:00:14.882
and we'll see the water is
actually a source of electrons,

00:00:14.882 --> 00:00:16.891
and we can use that to store energy

00:00:16.891 --> 00:00:19.308
in the form of ATP and NADPH,

00:00:20.234 --> 00:00:22.769
and as a by-product we
produce molecular oxygen,

00:00:22.769 --> 00:00:24.693
which is very important for us to breathe.

00:00:24.693 --> 00:00:26.558
And then that ATP and that NADPH

00:00:26.558 --> 00:00:28.186
can be used in the Calvin cycle,

00:00:28.186 --> 00:00:32.870
along with carbon dioxide,
to actually synthesize sugar.

00:00:32.870 --> 00:00:34.551
What we're gonna focus on in this video

00:00:34.551 --> 00:00:36.633
are the light-dependent reactions.

00:00:36.633 --> 00:00:39.335
How does this process right here work?

00:00:39.335 --> 00:00:40.729
And to help us think about this,

00:00:40.729 --> 00:00:44.812
we're going to zoom in
onto a thylakoid membrane.

00:00:46.172 --> 00:00:48.356
So this is a thylakoid right over here,

00:00:48.356 --> 00:00:50.607
sitting inside of the chloroplast.

00:00:50.607 --> 00:00:52.591
And if we zoom in on its membrane,

00:00:52.591 --> 00:00:54.514
we see it's a phospholipid bilayer,

00:00:54.514 --> 00:00:57.215
like many membranes
that we see in biology.

00:00:57.215 --> 00:00:58.875
And at first glance, this might seem

00:00:58.875 --> 00:01:00.555
like a very complex diagram,

00:01:00.555 --> 00:01:02.356
and that's because it
is a complex diagram,

00:01:02.356 --> 00:01:03.492
and you will often see things like this

00:01:03.492 --> 00:01:04.807
in your biology textbooks.

00:01:04.807 --> 00:01:06.312
They can be very intimidating,

00:01:06.312 --> 00:01:09.599
these proteins and molecules and complexes

00:01:09.599 --> 00:01:12.148
have very complicated-sounding names,

00:01:12.148 --> 00:01:14.502
but the general idea
of what's going on is,

00:01:14.502 --> 00:01:17.984
you'll hopefully find,
pretty straightforward.

00:01:17.984 --> 00:01:19.707
You have the energy from light,

00:01:19.707 --> 00:01:21.655
photons from light are going to,

00:01:21.655 --> 00:01:25.587
either directly or
indirectly, excite electrons.

00:01:25.587 --> 00:01:28.794
Those excited electrons,
they're in a high-energy state.

00:01:28.794 --> 00:01:32.132
They're gonna be transferred
from one molecule to another,

00:01:32.132 --> 00:01:34.214
and they're going to go
to lower energy states.

00:01:34.214 --> 00:01:35.705
That's what allows those transfers

00:01:35.705 --> 00:01:39.099
to be as spontaneous, for
them to actually occur.

00:01:39.099 --> 00:01:41.390
They're going from a high-energy state

00:01:41.390 --> 00:01:42.744
to a lower-energy state.

00:01:42.744 --> 00:01:43.801
The electrons are getting more

00:01:43.801 --> 00:01:45.091
and more and more comfortable,

00:01:45.091 --> 00:01:46.834
and some of that energy that's released

00:01:46.834 --> 00:01:48.817
as the electron goes
from a high-energy state

00:01:48.817 --> 00:01:50.318
to a lower-energy state

00:01:50.318 --> 00:01:54.485
is used to pump hydrogen
ions across the membrane.

00:01:56.261 --> 00:01:58.739
From the outside of the
membrane, in the stroma,

00:01:58.739 --> 00:02:00.761
to the inside of the membrane,

00:02:00.761 --> 00:02:03.257
to within the thylakoid lumen.

00:02:03.257 --> 00:02:07.424
So you are building a hydrogen
ion concentration gradient.

00:02:12.988 --> 00:02:15.659
Concentration gradient.

00:02:15.659 --> 00:02:17.995
Where you have a higher
concentration inside

00:02:17.995 --> 00:02:20.468
than you have outside.

00:02:20.468 --> 00:02:22.103
And this by itself,

00:02:22.103 --> 00:02:24.143
this concentration gradient as we'll see,

00:02:24.143 --> 00:02:26.213
can be used to fuel the production

00:02:26.213 --> 00:02:28.130
of ATP by ATP synthase,

00:02:29.496 --> 00:02:32.241
that those hydrogen ions
want to get back out.

00:02:32.241 --> 00:02:34.693
They wanna go down their
concentration gradient,

00:02:34.693 --> 00:02:37.984
and as they go back out
through the ATP synthase

00:02:37.984 --> 00:02:39.641
it essentially turns that motor

00:02:39.641 --> 00:02:43.808
that can jam the phosphate
group onto ADP to produce ATP.

00:02:45.225 --> 00:02:46.737
So one way to think about it,

00:02:46.737 --> 00:02:50.936
this is producing a hydrogen ion gradient.

00:02:50.936 --> 00:02:52.011
So we could do it this way,

00:02:52.011 --> 00:02:54.428
we could say H plus gradient,

00:02:55.758 --> 00:02:59.925
which is then being used
to produce the actual ATP.

00:03:01.068 --> 00:03:04.706
Now the electrons going
from a high-energy state

00:03:04.706 --> 00:03:07.491
to a lower-energy state in this part

00:03:07.491 --> 00:03:09.417
of the light-dependent reactions,

00:03:09.417 --> 00:03:11.894
that by itself isn't the only
thing that is contributing

00:03:11.894 --> 00:03:15.859
to the hydrogen ion
concentration gradient.

00:03:15.859 --> 00:03:17.857
Once that electron gets donated,

00:03:17.857 --> 00:03:19.869
you might say, well how
does it get replaced?

00:03:19.869 --> 00:03:22.113
Well the thing that's doing the donating,

00:03:22.113 --> 00:03:23.340
the thing that eventually gets excited

00:03:23.340 --> 00:03:24.639
and donates that electron,

00:03:24.639 --> 00:03:28.969
it's a chlorophyll a
variation called P680.

00:03:28.969 --> 00:03:31.629
P680 is referring to the
P stands for pigment,

00:03:31.629 --> 00:03:33.870
680 stands for 680 nano-meters,

00:03:33.870 --> 00:03:37.215
the wavelength of light
that it absorbs best.

00:03:37.215 --> 00:03:39.297
And so when it gets excited, it becomes

00:03:39.297 --> 00:03:43.093
you'll see the notation off of P680*,

00:03:43.093 --> 00:03:45.085
that's when it has an excited electron.

00:03:45.085 --> 00:03:49.229
And then after it gives away its electron,

00:03:49.229 --> 00:03:50.979
it becomes P680+

00:03:53.462 --> 00:03:55.257
with a positive charge.

00:03:55.257 --> 00:03:57.986
And this P680, we could call it P680 plus

00:03:57.986 --> 00:04:00.615
right over here, maybe a P680 ion,

00:04:00.615 --> 00:04:04.331
this is actually a very
strong oxidizing agent.

00:04:04.331 --> 00:04:06.268
One of the strongest,
if not the strongest,

00:04:06.268 --> 00:04:08.232
that we know in biological systems.

00:04:08.232 --> 00:04:11.997
And so it really likes to grab
electrons from other things.

00:04:11.997 --> 00:04:13.483
And the thing that is around

00:04:13.483 --> 00:04:16.739
that it can grab electrons
from is actually water.

00:04:16.739 --> 00:04:19.188
And so this is such a
strong oxidizing agent

00:04:19.188 --> 00:04:22.528
that it can essentially
oxidize the oxygen in water,

00:04:22.528 --> 00:04:23.761
and oxygen as itself.

00:04:23.761 --> 00:04:25.842
I mean, oxidizing is named after oxygen

00:04:25.842 --> 00:04:27.738
because oxygen is such a strong,

00:04:27.738 --> 00:04:30.732
it's so electronegative,
it's such a strong,

00:04:30.732 --> 00:04:34.160
it's the thing that's
normally doing the oxidizing.

00:04:34.160 --> 00:04:38.294
So anyway, it grabs its electrons,
once it gets this P680+,

00:04:38.294 --> 00:04:40.558
grabs an electron from water,

00:04:40.558 --> 00:04:43.272
and then the water essentially falls apart

00:04:43.272 --> 00:04:45.031
so you're left just with the oxygen

00:04:45.031 --> 00:04:46.616
and then the hydrogen ions.

00:04:46.616 --> 00:04:50.116
And so those hydrogen ions also contribute

00:04:51.806 --> 00:04:55.228
to the increased hydrogen ion
concentration on the inside.

00:04:55.228 --> 00:04:59.650
And this is where we get
the oxygen by-product

00:04:59.650 --> 00:05:00.540
right over here.

00:05:00.540 --> 00:05:02.825
Here we have one half of an
O2, so if you do this twice

00:05:02.825 --> 00:05:05.502
you're going to have a molecular oxygen.

00:05:05.502 --> 00:05:08.811
So, so far we've talked about
how the oxygen gets produced,

00:05:08.811 --> 00:05:11.629
we've talked about how
the ATP gets produced.

00:05:11.629 --> 00:05:13.397
What about the NADPH?

00:05:13.397 --> 00:05:17.251
Well we've started our
process in photosystem II.

00:05:17.251 --> 00:05:18.868
You might say, why's it
called photosystem II

00:05:18.868 --> 00:05:20.508
if that's where we start?

00:05:20.508 --> 00:05:21.578
Well it's actually that's because

00:05:21.578 --> 00:05:23.501
that's the second
photosystem to be discovered.

00:05:23.501 --> 00:05:25.990
You might say, what is a photosystem?

00:05:25.990 --> 00:05:28.330
Well these photosystems and complexes,

00:05:28.330 --> 00:05:30.906
they're combinations of
proteins and molecules,

00:05:30.906 --> 00:05:33.880
and photosystem in
particular has chlorophyll

00:05:33.880 --> 00:05:36.533
and variations of chlorophyll
and pigment molecules

00:05:36.533 --> 00:05:39.156
that are responsive to
light that are very easy,

00:05:39.156 --> 00:05:42.178
that have electrons that
can get excited by light,

00:05:42.178 --> 00:05:44.160
and they can transfer that energy

00:05:44.160 --> 00:05:48.359
back down to the P680 chlorophyll a pair,

00:05:48.359 --> 00:05:50.885
which then can have its electron excited

00:05:50.885 --> 00:05:53.618
and then it can give that
to an acceptor molecule

00:05:53.618 --> 00:05:56.469
and then it can go to
lower, lower energy states

00:05:56.469 --> 00:05:59.990
and pump those hydrogen ions out.

00:05:59.990 --> 00:06:02.980
But that's not the entire
light-dependent reactions.

00:06:02.980 --> 00:06:05.487
That electron can eventually make its way

00:06:05.487 --> 00:06:08.210
over to photosystem I, and
why's it called photosystem I?

00:06:08.210 --> 00:06:10.660
Well it's because the first
one that was discovered.

00:06:10.660 --> 00:06:12.525
In photosystem I, there's another

00:06:12.525 --> 00:06:15.143
chlorophyll a pair called P700,

00:06:15.143 --> 00:06:17.979
and that's because it optimally absorbs

00:06:17.979 --> 00:06:20.455
light of a wavelength of 700 nano-meters.

00:06:20.455 --> 00:06:22.496
And you have something
similar that happens,

00:06:22.496 --> 00:06:23.882
that light can either directly

00:06:23.882 --> 00:06:26.556
or indirectly excite its electron.

00:06:26.556 --> 00:06:29.243
And then that electron, as it
goes to a lower-energy level,

00:06:29.243 --> 00:06:30.757
it goes from one molecule to another,

00:06:30.757 --> 00:06:34.674
it can be used to reduce NADP+ into NADPH.

00:06:37.472 --> 00:06:40.961
And so that's where the NADPH comes from.

00:06:40.961 --> 00:06:45.781
And then once again, once the
P700 has given its electron,

00:06:45.781 --> 00:06:47.457
it wants an electron,

00:06:47.457 --> 00:06:49.361
and well it can get that from the electron

00:06:49.361 --> 00:06:52.627
that's been going from lower
to lower, lower energy states,

00:06:52.627 --> 00:06:55.500
that's essentially been
making its way from,

00:06:55.500 --> 00:06:57.260
you can conceptualize it as the electron

00:06:57.260 --> 00:07:00.126
that's been making its
way from photosystem II.

00:07:00.126 --> 00:07:01.867
And so that's why you'll
often see these diagrams.

00:07:01.867 --> 00:07:04.992
Lights come in, electron gets
energized, it gets excited,

00:07:04.992 --> 00:07:06.943
it goes to lower and lower energy states.

00:07:06.943 --> 00:07:08.489
As it's doing that it's being transferred

00:07:08.489 --> 00:07:09.803
from one molecule to another,

00:07:09.803 --> 00:07:11.728
being facilitated by enzymes.

00:07:11.728 --> 00:07:13.699
That energy, part of that energy

00:07:13.699 --> 00:07:15.704
is being used to transfer hydrogen ions

00:07:15.704 --> 00:07:19.371
into the thylakoid
lumen, into the interior.

00:07:20.205 --> 00:07:24.372
Then in photosystem I, you
have another excitation event.

00:07:25.393 --> 00:07:27.757
That thing that got excited
can grab that electron

00:07:27.757 --> 00:07:29.303
that went to lower, lower energy states,

00:07:29.303 --> 00:07:31.221
and its excited electron can once again

00:07:31.221 --> 00:07:33.813
be transferred from
one molecule to another

00:07:33.813 --> 00:07:37.177
in order to fuel or provide energy

00:07:37.177 --> 00:07:41.472
for NADP+ being converted into NADPH.

00:07:41.472 --> 00:07:43.323
And once again the whole idea

00:07:43.323 --> 00:07:46.065
of the hydrogen ion
concentration increasing here

00:07:46.065 --> 00:07:49.637
can fuel ATP synthase, which
allows us to jam a phosphate

00:07:49.637 --> 00:07:52.355
onto ADP to produce ATP.

00:07:52.355 --> 00:07:54.875
So that is where we actually
get all of these things

00:07:54.875 --> 00:07:58.458
and the by-product of
course is our oxygen.

00:07:59.361 --> 00:08:02.855
And if you wanted to see that same idea

00:08:02.855 --> 00:08:05.571
but kind of just thinking from
an energetic point of view

00:08:05.571 --> 00:08:06.759
without all of the complexity

00:08:06.759 --> 00:08:09.472
of seeing the physical
components involved,

00:08:09.472 --> 00:08:10.760
you see it right over here.

00:08:10.760 --> 00:08:14.927
Where you have light energy
comes, excites the electrons.

00:08:16.464 --> 00:08:19.618
Once the P680 has given
that electron away,

00:08:19.618 --> 00:08:21.500
it wants an electron really badly.

00:08:21.500 --> 00:08:23.576
It gets it from the water.

00:08:23.576 --> 00:08:24.984
And then as that electron goes

00:08:24.984 --> 00:08:27.012
to lower and lower and
lower energy states,

00:08:27.012 --> 00:08:29.601
it can eventually be grabbed by P700

00:08:29.601 --> 00:08:32.144
that has given away its own electron.

00:08:32.144 --> 00:08:36.379
And then that electron
that was excited at P700

00:08:36.379 --> 00:08:38.287
by, once again, more light energy,

00:08:38.287 --> 00:08:41.230
that can be transferred
from one molecule to another

00:08:41.230 --> 00:08:43.730
to fuel the creation of NADPH.

00:08:44.788 --> 00:08:48.850
And this part right over here,
this phase right over here,

00:08:48.850 --> 00:08:51.397
as the energy goes from
a high-energy state to a-

00:08:51.397 --> 00:08:54.227
as the electron goes
from a high-energy state

00:08:54.227 --> 00:08:55.492
to a lower energy state,

00:08:55.492 --> 00:08:57.996
fuels the pumping of hydrogen protons

00:08:57.996 --> 00:09:00.246
into the actual thylakoid.


Breaking down photosynthesis stages

WEBVTT
Kind: captions
Language: en

00:00:00.272 --> 00:00:01.377
- [Voiceover] So, I'm gonna give

00:00:01.377 --> 00:00:04.644
another quick overview of photosynthesis.

00:00:04.644 --> 00:00:08.811
And this time I'm gonna break
it down into two big stages.

00:00:09.864 --> 00:00:11.710
So, as you are probably familiar,

00:00:11.710 --> 00:00:13.872
just looking at the word, photosynthesis.

00:00:13.872 --> 00:00:14.888
It essentially has two parts,

00:00:14.888 --> 00:00:16.526
it has photo and it has synthesis.

00:00:16.526 --> 00:00:18.747
The photo is referring to

00:00:18.747 --> 00:00:20.829
that it's going to use light somehow.

00:00:20.829 --> 00:00:22.993
And what's it going to do
with that light energy?

00:00:22.993 --> 00:00:24.987
Well, it's going to synthesize something.

00:00:24.987 --> 00:00:27.816
And, in particular, what
it's going to synthesize,

00:00:27.816 --> 00:00:29.322
as we'll see, is sugar.

00:00:29.322 --> 00:00:33.266
So, we are going to go
from energy in light,

00:00:33.266 --> 00:00:36.888
let me just write light, light energy,

00:00:36.888 --> 00:00:41.151
and we're going to use that
light energy to synthesize,

00:00:41.151 --> 00:00:42.901
to synthesize, sugar,

00:00:44.734 --> 00:00:45.858
very broadly speaking.

00:00:45.858 --> 00:00:48.750
Obviously this is a very,
very high-level overview.

00:00:48.750 --> 00:00:51.623
The light energy isn't
the only input here.

00:00:51.623 --> 00:00:54.751
We're also going to need some water

00:00:54.751 --> 00:00:55.886
and as we go into future videos,

00:00:55.886 --> 00:00:57.297
we'll see what that water's used for.

00:00:57.297 --> 00:00:59.428
It's actually a source of electrons.

00:00:59.428 --> 00:01:00.563
To do this,

00:01:00.563 --> 00:01:03.711
to make use of that light energy, frankly.

00:01:03.711 --> 00:01:08.330
And we're also going to
need some carbon dioxide,

00:01:08.330 --> 00:01:11.034
really as a source of carbons,

00:01:11.034 --> 00:01:14.113
because there's a lot of
carbon in those sugars.

00:01:14.113 --> 00:01:15.879
We're essentially going to fix the carbon.

00:01:15.879 --> 00:01:18.790
We're gonna take it from
this carbon dioxide gas,

00:01:18.790 --> 00:01:21.524
and we're going to incorporate
it into organic molecules

00:01:21.524 --> 00:01:24.535
and eventually into the sugar.

00:01:24.535 --> 00:01:26.232
And sugar isn't the only output.

00:01:26.232 --> 00:01:31.078
Another bi-product of this
process is molecular oxygen.

00:01:31.078 --> 00:01:35.726
Once you strip a couple of
electrons from the water,

00:01:35.726 --> 00:01:38.983
and the hydrogen ions are
stripped away from it as well,

00:01:38.983 --> 00:01:41.566
all you're left with is oxygen.

00:01:43.029 --> 00:01:44.085
And you do that twice,

00:01:44.085 --> 00:01:46.582
then you have o two and
you have molecular oxygen.

00:01:46.582 --> 00:01:49.029
And this is a bi-product
of photosynthesis,

00:01:49.029 --> 00:01:50.806
but you can imagine this is very important

00:01:50.806 --> 00:01:52.760
to life on earth as we know it,

00:01:52.760 --> 00:01:54.004
in particular for us.

00:01:54.004 --> 00:01:55.208
We would have trouble breathing

00:01:55.208 --> 00:01:59.520
if this was not a bi-product
of photosynthesis.

00:01:59.520 --> 00:02:01.346
Now what I'm gonna do
now is break this out

00:02:01.346 --> 00:02:02.925
into two stages.

00:02:02.925 --> 00:02:03.892
And these two stages,

00:02:03.892 --> 00:02:07.392
we can call the light-dependent reactions.

00:02:08.501 --> 00:02:10.668
Light-dependent reactions,

00:02:16.120 --> 00:02:18.192
and then the second stage,

00:02:18.192 --> 00:02:21.034
I will call the Calvin cycle.

00:02:21.034 --> 00:02:22.867
Calvin, Calvin, cycle.

00:02:25.080 --> 00:02:26.669
And as the name implies,

00:02:26.669 --> 00:02:30.094
the light-dependent reactions
are dependent on light.

00:02:30.094 --> 00:02:31.722
So, what's happening here is,

00:02:31.722 --> 00:02:34.307
we're gonna take light energy.

00:02:34.307 --> 00:02:35.363
Light energy.

00:02:35.363 --> 00:02:39.530
Plus we're gonna take the
water as a source of electrons,

00:02:41.620 --> 00:02:44.067
and we're going to use these two things.

00:02:44.067 --> 00:02:47.651
We're going to use these
two things to produce,

00:02:47.651 --> 00:02:50.099
to produce, let me write
this in another color,

00:02:50.099 --> 00:02:52.099
to produce ATP from ADP,

00:02:54.639 --> 00:02:56.149
so we're gonna produce ATP,

00:02:56.149 --> 00:02:57.799
which is a store of energy,

00:02:57.799 --> 00:03:01.966
and we're also going to
reduce NADP plus into NADPH,

00:03:07.107 --> 00:03:11.010
which has energy as a
strong reducing agent.

00:03:11.010 --> 00:03:13.221
So this is what is
happening, broadly speaking,

00:03:13.221 --> 00:03:14.632
in the light reactions.

00:03:14.632 --> 00:03:16.872
And then in the Calvin
cycle, what we're gonna do

00:03:16.872 --> 00:03:19.003
is we're gonna take these products

00:03:19.003 --> 00:03:22.142
of the light-dependent reactions,

00:03:22.142 --> 00:03:25.642
so we're gonna take our ATP and our NADPH,

00:03:28.981 --> 00:03:31.776
and we can use their energy in conjunction

00:03:31.776 --> 00:03:34.194
with some carbon dioxide,

00:03:34.194 --> 00:03:37.068
with some carbon dioxide,

00:03:37.068 --> 00:03:38.804
in order to produce,

00:03:38.804 --> 00:03:41.538
in order to produce, sugar.

00:03:41.538 --> 00:03:43.705
In order to produce sugar.

00:03:45.132 --> 00:03:47.658
And, let me see, have
I got everything here?

00:03:47.658 --> 00:03:50.145
Oh, of course, I'm missing
one of the bi-products

00:03:50.145 --> 00:03:51.448
of the light-dependent reactions.

00:03:51.448 --> 00:03:53.156
A very important one.

00:03:53.156 --> 00:03:57.133
I'm missing the molecular,
the molecular oxygen.

00:03:57.133 --> 00:04:00.547
So, once again, this is what
makes up photosynthesis,

00:04:00.547 --> 00:04:02.906
but you can break it up
into these two segments.

00:04:02.906 --> 00:04:05.353
Light-dependent reaction
is using the energy

00:04:05.353 --> 00:04:09.884
from photons in light along
with electrons from the water

00:04:09.884 --> 00:04:13.717
to produce, to store
energy, as ATP and NADPH,

00:04:14.848 --> 00:04:18.538
and has oxygen, molecular
oxygen, as a bi-product.

00:04:18.538 --> 00:04:20.424
In order for it to get
one molecular oxygen,

00:04:20.424 --> 00:04:23.138
you're gonna have to need
two of these water molecules.

00:04:23.138 --> 00:04:25.950
And then, as we go into the Calvin cycle,

00:04:25.950 --> 00:04:28.990
we can take these, the ATP and the NADPH,

00:04:28.990 --> 00:04:31.526
along with some carbon dioxide,

00:04:31.526 --> 00:04:35.276
and we can use that to
actually store energy

00:04:35.276 --> 00:04:36.609
as actual sugar.

00:04:38.187 --> 00:04:39.460
And as we'll do in future videos,

00:04:39.460 --> 00:04:41.059
we'll go into more depth and see

00:04:41.059 --> 00:04:43.062
what exactly happens in these
light-dependent reactions,

00:04:43.062 --> 00:04:46.879
and what exactly happens
in the Calvin cycle.


Big takeaways from the Civil War

WEBVTT
Kind: captions
Language: en

00:00:00.338 --> 00:00:02.924
- [Voiceover] We've been
discussing the American Civil War,

00:00:02.924 --> 00:00:05.757
which lasted from 1861 until 1865.

00:00:07.476 --> 00:00:11.396
It was the deadliest conflict
in all of American history,

00:00:11.396 --> 00:00:15.063
in which 620,000 Americans
lost their lives.

00:00:17.011 --> 00:00:20.440
We briefly went over
the very end of the war,

00:00:20.440 --> 00:00:24.602
as Grant caught up to Lee at Appomattox.

00:00:24.602 --> 00:00:28.802
And Lee surrendered, and
then confederate sympathizer

00:00:28.802 --> 00:00:32.265
and sometimes spy, John
Wilkes Booth assassinated

00:00:32.265 --> 00:00:34.460
American President Abraham Lincoln.

00:00:34.460 --> 00:00:37.046
Lincoln was followed in
office by Andrew Johnson,

00:00:37.046 --> 00:00:40.239
who will preside over reconstruction.

00:00:40.239 --> 00:00:43.274
But now that we've talked
about the progress of war,

00:00:43.274 --> 00:00:47.909
from the first fighting at
Fort Sumter in April of 1861,

00:00:47.909 --> 00:00:51.492
to the last surrenders
in November of 1865,

00:00:52.538 --> 00:00:55.345
I'd like to take just a
few minutes to contemplate

00:00:55.345 --> 00:00:58.299
what some of the bigger
issues that the Civil War

00:00:58.299 --> 00:01:00.965
raises are in American History.

00:01:00.965 --> 00:01:03.507
And what impact will it have on the future

00:01:03.507 --> 00:01:04.924
of American life?

00:01:07.256 --> 00:01:09.743
Well certainly one of the
most important things,

00:01:09.743 --> 00:01:12.681
if not the most important thing
to come out of the Civil War

00:01:12.681 --> 00:01:14.514
is the end of slavery.

00:01:15.958 --> 00:01:20.487
You know, before the Civil
War, before the 1850s,

00:01:20.487 --> 00:01:23.620
your average White
American, who lived in say

00:01:23.620 --> 00:01:25.703
Pennsylvania or Kentucky,

00:01:26.837 --> 00:01:28.920
probably wasn't very fond

00:01:29.943 --> 00:01:34.087
of slavery, but probably
wouldn't have gone

00:01:34.087 --> 00:01:37.745
out of his or her way to
take a stand against it.

00:01:37.745 --> 00:01:40.644
I think Lincoln himself
was very representative

00:01:40.644 --> 00:01:43.678
of this view, in that, he hated slavery,

00:01:43.678 --> 00:01:47.076
but he thought that he had
no right to interfere with it

00:01:47.076 --> 00:01:49.481
and he mostly just
wanted to make sure that

00:01:49.481 --> 00:01:53.066
slave owners couldn't bring
enslaved people out west

00:01:53.066 --> 00:01:56.866
to take lands from, what
he saw as hardworking,

00:01:56.866 --> 00:01:59.252
deserving, poorer Whites.

00:01:59.252 --> 00:02:03.128
By the end of the Civil
War, no one could argue

00:02:03.128 --> 00:02:05.801
that African Americans,
especially in the north

00:02:05.801 --> 00:02:08.134
did not deserve citizenship.

00:02:09.100 --> 00:02:13.333
Throughout the Civil
War, African Americans

00:02:13.333 --> 00:02:17.500
proved their important to the
nation, time and time again.

00:02:18.545 --> 00:02:21.139
Especially through their
military service in units

00:02:21.139 --> 00:02:23.996
like the 54th Massachusetts for example.

00:02:23.996 --> 00:02:28.163
And so, for the approximately
four and a half million

00:02:29.458 --> 00:02:32.708
enslaved people who lived in the south,

00:02:33.848 --> 00:02:36.098
they now had their freedom.

00:02:38.298 --> 00:02:41.438
And the story of what
happens to these people

00:02:41.438 --> 00:02:44.598
who have been freed from bondage,

00:02:44.598 --> 00:02:47.366
is perhaps the most interesting,

00:02:47.366 --> 00:02:50.632
and important story of American history.

00:02:50.632 --> 00:02:53.898
Does all men are created equal mean

00:02:53.898 --> 00:02:56.873
all men and women are created equal?

00:02:56.873 --> 00:03:00.272
That is the question that
will occupy the nation

00:03:00.272 --> 00:03:04.043
in one way or another, up
until the present, really.

00:03:04.043 --> 00:03:07.792
Another major important
takeaway from the Civil War

00:03:07.792 --> 00:03:11.388
is that that Civil War
represented a movement

00:03:11.388 --> 00:03:12.776
in the United States,

00:03:12.776 --> 00:03:14.609
from a union of states

00:03:19.975 --> 00:03:20.975
to a nation.

00:03:23.048 --> 00:03:25.285
And you can even see how
Abraham Lincoln's thinking

00:03:25.285 --> 00:03:28.292
on this changes over
the course of the war.

00:03:28.292 --> 00:03:31.555
He starts to even use the word nation

00:03:31.555 --> 00:03:32.924
more and more.

00:03:32.924 --> 00:03:35.489
Throughout the early part of the history

00:03:35.489 --> 00:03:39.050
of the United States, you
see this balance of power

00:03:39.050 --> 00:03:42.625
between states and between
the Federal Government

00:03:42.625 --> 00:03:45.361
really shifting all of the time.

00:03:45.361 --> 00:03:48.916
You see things like the
nullification crisis in the 1830s

00:03:48.916 --> 00:03:51.933
when South Carolina said
we don't like this tariff.

00:03:51.933 --> 00:03:55.293
We think that as a state,
the union is composed

00:03:55.293 --> 00:03:58.059
out of the consent of
the individual states,

00:03:58.059 --> 00:04:01.248
and therefore the state
has the right to nullify

00:04:01.248 --> 00:04:02.843
a law it doesn't agree with.

00:04:02.843 --> 00:04:07.154
The same sort of situation
happened in 1860 over slavery.

00:04:07.154 --> 00:04:09.463
The southern states
believed that Lincoln would

00:04:09.463 --> 00:04:12.418
outlaw slavery, and thought
that it would be more

00:04:12.418 --> 00:04:15.707
important to secede as a group of states

00:04:15.707 --> 00:04:18.456
protecting in their words,
their states rights,

00:04:18.456 --> 00:04:21.240
then to be subject to
the laws of the nation.

00:04:21.240 --> 00:04:24.990
Well the Civil War ends
that kind of thinking.

00:04:24.990 --> 00:04:28.610
In fact you even see it from
how people write the name

00:04:28.610 --> 00:04:29.799
of this country.

00:04:29.799 --> 00:04:32.896
Frequently it might have been
said before the Civil War

00:04:32.896 --> 00:04:34.563
these United States.

00:04:38.295 --> 00:04:41.755
It's a group of states that are united.

00:04:41.755 --> 00:04:45.922
After the Civil War, it
becomes the United States.

00:04:46.773 --> 00:04:48.773
One nation, indivisible.

00:04:50.121 --> 00:04:54.966
And so this is the moment
when the Federal Government

00:04:54.966 --> 00:04:56.799
really begins to grow.

00:04:59.182 --> 00:05:02.893
You know during war time,
the north had to really

00:05:02.893 --> 00:05:06.310
organize as a nation to provide resources

00:05:07.412 --> 00:05:09.994
for their populace and for the soldiers

00:05:09.994 --> 00:05:13.553
and so the President gained powers that

00:05:13.553 --> 00:05:17.242
he had never had before,
and the Federal bureaucracy

00:05:17.242 --> 00:05:19.325
itself grew a great deal.

00:05:20.232 --> 00:05:23.961
And you're going to see this
throughout the 20th century,

00:05:23.961 --> 00:05:28.021
really up until the 1970s
that the Federal Government

00:05:28.021 --> 00:05:32.188
in the United States is going
to have more and more power.

00:05:37.382 --> 00:05:40.591
A third important takeaway
from the Civil War

00:05:40.591 --> 00:05:44.758
is that during the Civil
War the north industrialized

00:05:45.674 --> 00:05:48.191
to produce all of the goods

00:05:48.191 --> 00:05:52.024
and material that the
north needed to succeed.

00:05:53.970 --> 00:05:57.709
They built factories, and railroads

00:05:57.709 --> 00:06:00.193
and those factories and railroads,

00:06:00.193 --> 00:06:03.933
and all the rest of the
impressive engineering

00:06:03.933 --> 00:06:05.981
that went into winning the war

00:06:05.981 --> 00:06:09.314
is then going to be turned toward making

00:06:10.513 --> 00:06:12.346
an industrial behemoth

00:06:13.917 --> 00:06:16.096
in the post war era.

00:06:16.096 --> 00:06:20.720
So, a lot of things that
started during the Civil War

00:06:20.720 --> 00:06:24.200
in terms of national
industrialization really carry

00:06:24.200 --> 00:06:29.031
on in the post war era,
known as the Gilded Age.

00:06:29.031 --> 00:06:32.225
That help the United
States become the worlds

00:06:32.225 --> 00:06:35.137
premiere industrial
power, and later, based

00:06:35.137 --> 00:06:37.198
on that industrial
power, one of the worlds

00:06:37.198 --> 00:06:39.328
premiere political powers.

00:06:39.328 --> 00:06:42.938
Another thing that is
not often talked about

00:06:42.938 --> 00:06:46.855
with the Civil War is
the growing role of women

00:06:47.710 --> 00:06:50.332
in the United States polity.

00:06:50.332 --> 00:06:53.165
Ya know in the American Civil War,

00:06:54.347 --> 00:06:59.249
at first it was very taboo
for a woman of good birth

00:06:59.249 --> 00:07:01.386
to go and become a nurse.

00:07:01.386 --> 00:07:03.736
But as the war progressed, that kind of

00:07:03.736 --> 00:07:06.810
Victorian thinking, believing
that a woman belonged

00:07:06.810 --> 00:07:10.916
only to a very feminine and
domestic sphere of life,

00:07:10.916 --> 00:07:12.520
really had to fade away

00:07:12.520 --> 00:07:16.065
in the face of the
reality that women needed

00:07:16.065 --> 00:07:17.803
to play a role in the war.

00:07:17.803 --> 00:07:20.553
In the north women became nurses.

00:07:21.734 --> 00:07:25.628
They helped to chair the
American Sanitary Commission,

00:07:25.628 --> 00:07:27.916
which was one of the key hospital groups

00:07:27.916 --> 00:07:29.606
of the time period.

00:07:29.606 --> 00:07:33.330
And in the south, many
women also really took over

00:07:33.330 --> 00:07:36.268
the running of family farms

00:07:36.268 --> 00:07:38.185
as White men went away,

00:07:40.249 --> 00:07:44.190
White women, poorer
White women for example

00:07:44.190 --> 00:07:46.637
would be in charge of a farm themselves.

00:07:46.637 --> 00:07:49.894
A White woman who belonged
to a slave owning family

00:07:49.894 --> 00:07:52.787
herself, would then have
charge of enslaved people.

00:07:52.787 --> 00:07:55.338
So women took a much
more leading role during

00:07:55.338 --> 00:07:56.652
the Civil War.

00:07:56.652 --> 00:07:59.653
After the Civil War,
some of that falls away.

00:07:59.653 --> 00:08:02.102
In fact, there's a really difficult moment

00:08:02.102 --> 00:08:05.104
in the movement for women's rights when

00:08:05.104 --> 00:08:09.271
in 1870, the 15th amendment
granted African American

00:08:10.184 --> 00:08:13.267
men the right to vote, but not women.

00:08:14.980 --> 00:08:18.086
And so the women's movement
will take some time

00:08:18.086 --> 00:08:20.482
to regroup in the late 19th century.

00:08:20.482 --> 00:08:22.916
But the Civil War, like many later wars,

00:08:22.916 --> 00:08:24.520
brought women outside the home.

00:08:24.520 --> 00:08:27.750
And after the war they were
not anxious to go back there.

00:08:27.750 --> 00:08:31.515
They became involved in many
charitable organizations,

00:08:31.515 --> 00:08:34.095
often known as social housekeeping.

00:08:34.095 --> 00:08:38.262
As women do more and more
things outside the home.

00:08:41.657 --> 00:08:44.965
Which will eventually grow
into the women's movement

00:08:44.965 --> 00:08:47.437
of the early 20th
century, and lead to women

00:08:47.437 --> 00:08:48.709
getting the right to vote.

00:08:48.709 --> 00:08:52.159
This is just a small
sampling of some of the

00:08:52.159 --> 00:08:56.360
major impacts that the Civil
War had on the United States.

00:08:56.360 --> 00:08:58.861
Often when we think about
United States history,

00:08:58.861 --> 00:09:02.783
we think about it cutting
off at the Civil War.

00:09:02.783 --> 00:09:05.122
Most college courses
or high school courses

00:09:05.122 --> 00:09:08.407
are organized the US before the Civil War,

00:09:08.407 --> 00:09:10.422
and the US after the Civil War,

00:09:10.422 --> 00:09:12.551
because it's a really
defining moment in our

00:09:12.551 --> 00:09:14.656
nations history for these reasons,

00:09:14.656 --> 00:09:16.157
and for many others.

00:09:16.157 --> 00:09:18.382
The United States entered the Civil War

00:09:18.382 --> 00:09:22.049
a loose union of states
divided by territory

00:09:23.148 --> 00:09:27.169
and beliefs, and exited the
Civil War a single nation.

00:09:27.169 --> 00:09:32.003
Modern, industrial, peopled
by an incredibly diverse

00:09:32.003 --> 00:09:35.957
range of citizens from all over the world.

00:09:35.957 --> 00:09:37.898
In other words, after the Civil War,

00:09:37.898 --> 00:09:40.625
the United States will
really come into its own.

00:09:40.625 --> 00:09:42.902
And that's because the Civil
War was the moment when

00:09:42.902 --> 00:09:44.722
the United States grew up.

00:09:44.722 --> 00:09:48.869
The United States in 1870,
looked a lot more like

00:09:48.869 --> 00:09:53.014
the year 1900, then it did the year 1860.

00:09:53.014 --> 00:09:57.131
The 13th amendment, and later
the 14th and 15th amendments

00:09:57.131 --> 00:10:00.388
ruled that people of African
descent were citizens

00:10:00.388 --> 00:10:01.901
of the United States.

00:10:01.901 --> 00:10:04.970
Remember, beforehand,
enslaved people in the south

00:10:04.970 --> 00:10:07.295
counted for only 3/5ths of a person,

00:10:07.295 --> 00:10:09.442
and that person couldn't vote,

00:10:09.442 --> 00:10:13.018
move freely, or own his or her own labor,

00:10:13.018 --> 00:10:14.711
not to mention their own life.

00:10:14.711 --> 00:10:17.860
The Civil War decided
once and for all that

00:10:17.860 --> 00:10:19.964
everyone born in the United States

00:10:19.964 --> 00:10:21.885
was a United States citizen.

00:10:21.885 --> 00:10:25.844
But what citizenship really
meant for African Americans,

00:10:25.844 --> 00:10:29.305
for women, for Native
Americans and immigrants,

00:10:29.305 --> 00:10:30.739
even for Whites.

00:10:30.739 --> 00:10:32.940
Was still something that
would be hammered out

00:10:32.940 --> 00:10:36.182
through the rest of the
19th century and the 20th.

00:10:36.182 --> 00:10:39.778
After the Civil War, the
old problems of sectional

00:10:39.778 --> 00:10:42.775
tension and states
rights, were put to rest,

00:10:42.775 --> 00:10:44.810
but they were replaced by new problems.

00:10:44.810 --> 00:10:47.142
Problems of modern America.

00:10:47.142 --> 00:10:50.323
Industrialization, poverty, immigration,

00:10:50.323 --> 00:10:53.574
and so is the guns of
the Civil War fell quiet,

00:10:53.574 --> 00:10:57.741
the United States embarked
into a new era, The Gilded Age.


Later stages of the Civil War part 3

WEBVTT
Kind: captions
Language: en

00:00:00.384 --> 00:00:01.382
- [Voiceover] So in the last video,

00:00:01.382 --> 00:00:05.839
we talked about the year 1864
in the American Civil War,

00:00:05.839 --> 00:00:09.692
and now we're getting down
to the very end of the war.

00:00:09.692 --> 00:00:13.109
In 1864, William Tecumseh Sherman had his

00:00:13.997 --> 00:00:16.806
sort of famous march to the sea,

00:00:16.806 --> 00:00:20.563
where he captured Atlanta and
then carried on a total war

00:00:20.563 --> 00:00:23.932
through the state of Georgia to Savannah,

00:00:23.932 --> 00:00:26.325
and from Savannah he turns north

00:00:26.325 --> 00:00:29.928
and starts heading to the forces of Grant,

00:00:29.928 --> 00:00:33.145
so he can back him up in a
final victory against Lee,

00:00:33.145 --> 00:00:36.379
who has encamped in Richmond.

00:00:36.379 --> 00:00:40.546
Meanwhile, Abraham Lincoln
wins the election of 1864,

00:00:42.270 --> 00:00:45.770
and is ready to bring this war to a close.

00:00:47.077 --> 00:00:49.318
So let's move on to 1865.

00:00:49.318 --> 00:00:52.456
A lot happens very quickly in 1865,

00:00:52.456 --> 00:00:54.275
starting with, in January,

00:00:54.275 --> 00:00:56.234
Congress passed the 13th Amendment.

00:00:56.234 --> 00:01:00.317
The 13th Amendment outlawed
slavery for all time.

00:01:01.314 --> 00:01:05.397
It's clear that when the
south is brought back in

00:01:06.560 --> 00:01:08.720
to the United States, it is
going to be brought back in

00:01:08.720 --> 00:01:11.672
without slavery, there
is no option for slavery

00:01:11.672 --> 00:01:14.577
in the United States going forward.

00:01:14.577 --> 00:01:18.744
Now Grant, after his incredible
victory in Tennessee,

00:01:21.119 --> 00:01:25.301
in Vicksburg, has been going
after Lee's army in Virginia.

00:01:25.301 --> 00:01:29.234
Now Lee has holed up in
Richmond and eventually,

00:01:29.234 --> 00:01:31.873
he realizes his forces
can't stay there anymore,

00:01:31.873 --> 00:01:35.056
they can't hold the city, so
in the beginning of April,

00:01:35.056 --> 00:01:38.884
they evacuate Richmond and on April 3rd,

00:01:38.884 --> 00:01:42.858
the United States forces occupy Richmond.

00:01:42.858 --> 00:01:44.923
Abraham Lincoln himself actually goes down

00:01:44.923 --> 00:01:46.943
to visit Richmond, which
he'd never been to before,

00:01:46.943 --> 00:01:51.143
and he even goes to the
government building in Richmond

00:01:51.143 --> 00:01:54.997
where Confederate President
Jefferson Davis had governed,

00:01:54.997 --> 00:01:57.418
and goes into his office.

00:01:57.418 --> 00:02:01.891
He's there less than 48 hours
after Davis himself had left.

00:02:01.891 --> 00:02:06.381
And then events, after that,
events take place very quickly.

00:02:06.381 --> 00:02:09.419
So Lee falls back from
Richmond to Petersburg,

00:02:09.419 --> 00:02:12.504
and Grant is kind of
marking him the whole time,

00:02:12.504 --> 00:02:16.254
and they retreat across
Virginia to the west,

00:02:17.267 --> 00:02:19.261
Lee is probably heading for Lynchburg,

00:02:19.261 --> 00:02:23.428
and Grant manages to catch
up with him at Appomattox.

00:02:26.854 --> 00:02:29.385
At first, Lee thinks that he's actually

00:02:29.385 --> 00:02:31.213
going to fight at Appomattox,

00:02:31.213 --> 00:02:33.280
and then he realizes he just does not

00:02:33.280 --> 00:02:37.882
have the men necessary, so
he invites Grant to come

00:02:37.882 --> 00:02:42.154
and have a parlay for
surrender, and they meet,

00:02:42.154 --> 00:02:45.567
this is actually a picture
of Lee outside the house

00:02:45.567 --> 00:02:48.178
in Appomattox courthouse, Virginia,

00:02:48.178 --> 00:02:49.904
where he surrendered the Army of

00:02:49.904 --> 00:02:52.431
Northern Virginia to Grant.

00:02:52.431 --> 00:02:55.546
Now that is not the actual
end of the Civil War,

00:02:55.546 --> 00:02:59.850
but it's kind of the end
for all intents and purposes

00:02:59.850 --> 00:03:02.578
because Lee is the General-in-Chief

00:03:02.578 --> 00:03:05.047
of the Confederate Armies.

00:03:05.047 --> 00:03:08.476
Grant is likewise for the United States.

00:03:08.476 --> 00:03:10.419
And after this point, it's just gonna be

00:03:10.419 --> 00:03:12.539
kind of a matter of
time until all the rest

00:03:12.539 --> 00:03:15.651
of the Confederate armies surrender.

00:03:15.651 --> 00:03:18.809
So there's great celebration
in Washington, D.C.,

00:03:18.809 --> 00:03:23.336
everyone is very happy, finally
this four year long war,

00:03:23.336 --> 00:03:26.919
where 620,000 Americans
have died, is over,

00:03:29.212 --> 00:03:32.280
and Abraham Lincoln
goes and gives a speech,

00:03:32.280 --> 00:03:35.408
talking about what Reconstruction
is going to be like.

00:03:35.408 --> 00:03:39.575
And in this speech, he lays
out that African Americans,

00:03:40.542 --> 00:03:43.259
after the Civil War, are
going to have citizenship,

00:03:43.259 --> 00:03:45.862
at least some of them,
and the right to vote,

00:03:45.862 --> 00:03:48.883
which is in keeping with
everything that he's really said

00:03:48.883 --> 00:03:51.298
since the Emancipation Proclamation.

00:03:51.298 --> 00:03:53.312
But what he does not
know, is that this man,

00:03:53.312 --> 00:03:56.747
John Wilkes Booth, is
in the crowd that day,

00:03:56.747 --> 00:03:59.146
listening to him, and
when he hears Lincoln say

00:03:59.146 --> 00:04:01.557
that African Americans are
gonna have citizenship,

00:04:01.557 --> 00:04:03.069
they're gonna have the right to vote,

00:04:03.069 --> 00:04:05.385
he vows to kill Lincoln.

00:04:05.385 --> 00:04:07.746
John Wilkes Booth is really
interesting character,

00:04:07.746 --> 00:04:10.751
we only know so much about him.

00:04:10.751 --> 00:04:13.722
He himself was a famous actor, in fact,

00:04:13.722 --> 00:04:16.499
Lincoln had seen him
perform a number of times,

00:04:16.499 --> 00:04:19.834
and liked him, even invited
him to the White House,

00:04:19.834 --> 00:04:21.437
cause he thought he was a great actor,

00:04:21.437 --> 00:04:24.593
but Booth refused to go and see Lincoln.

00:04:24.593 --> 00:04:27.308
And he was from a family of famous actors,

00:04:27.308 --> 00:04:29.540
I think kind of a modern-day equivalent

00:04:29.540 --> 00:04:31.998
might be the Sheen family.

00:04:31.998 --> 00:04:35.811
Booth had a famous brother
who was also an actor,

00:04:35.811 --> 00:04:38.918
and a famous father who was also an actor,

00:04:38.918 --> 00:04:42.380
just like Martin Sheen's
sons are Emilio Estevez

00:04:42.380 --> 00:04:44.301
and Charlie Sheen today.

00:04:44.301 --> 00:04:47.135
So this would be like, if
Emilio Estevez or Charlie Sheen

00:04:47.135 --> 00:04:49.258
suddenly decided to murder the President,

00:04:49.258 --> 00:04:51.640
which would be a pretty
incredibly big deal,

00:04:51.640 --> 00:04:53.481
just as it was then.

00:04:53.481 --> 00:04:55.611
Booth was a Confederate sympathizer,

00:04:55.611 --> 00:04:59.469
and almost certainly a Confederate spy

00:04:59.469 --> 00:05:02.052
who had gone up to Canada at some time

00:05:02.052 --> 00:05:06.923
to plot some movement on
behalf of the Confederacy.

00:05:06.923 --> 00:05:11.570
He was an outright racist,
I think the part where

00:05:11.570 --> 00:05:14.166
Lincoln said African Americans
would have citizenship

00:05:14.166 --> 00:05:16.327
was what pushed him over the edge

00:05:16.327 --> 00:05:18.459
into assassinating Lincoln.

00:05:18.459 --> 00:05:22.037
Originally he had actually
planned to kidnap Lincoln,

00:05:22.037 --> 00:05:25.873
and ransom him for the
end of the Civil War,

00:05:25.873 --> 00:05:30.095
but after Lee surrenders,
Booth's plan changes.

00:05:30.095 --> 00:05:32.469
He wants to basically
decapitate the government,

00:05:32.469 --> 00:05:35.483
so he conspires with a
couple of other people,

00:05:35.483 --> 00:05:38.834
and they plan that they're going to kill

00:05:38.834 --> 00:05:41.657
all the highest people
in government at once.

00:05:41.657 --> 00:05:43.431
So they're going to kill Lincoln,

00:05:43.431 --> 00:05:45.606
they're going to kill General Grant,

00:05:45.606 --> 00:05:48.412
they're going to kill William Seward,

00:05:48.412 --> 00:05:49.696
the secretary of state,

00:05:49.696 --> 00:05:52.846
and they're going to kill Andrew Johnson,

00:05:52.846 --> 00:05:53.984
the Vice-President.

00:05:53.984 --> 00:05:55.610
And Booth thinks that perhaps,

00:05:55.610 --> 00:05:57.887
in this moment of panic that follows

00:05:57.887 --> 00:06:02.231
the decapitation of the entire
United States government,

00:06:02.231 --> 00:06:05.857
that perhaps something positive
for the south with happen.

00:06:05.857 --> 00:06:08.223
Remember, they had hoped
that getting rid of Lincoln

00:06:08.223 --> 00:06:12.146
in the election of 1864
might result in putting

00:06:12.146 --> 00:06:14.675
a government more favorable to the south

00:06:14.675 --> 00:06:16.911
in office to the north,
which didn't happen,

00:06:16.911 --> 00:06:20.459
so perhaps Booth wants to
do the same thing this time.

00:06:20.459 --> 00:06:23.375
So Booth reads in the
newspaper that Abraham Lincoln

00:06:23.375 --> 00:06:26.980
is going to be attending
a play at Ford's Theater

00:06:26.980 --> 00:06:28.063
that evening.

00:06:30.266 --> 00:06:33.422
And Booth is a regular at Ford's Theater,

00:06:33.422 --> 00:06:35.605
in fact, he even has his
mail delivered there,

00:06:35.605 --> 00:06:37.760
so it's kind of his home away from home.

00:06:37.760 --> 00:06:40.339
And when Booth goes to the theater

00:06:40.339 --> 00:06:42.289
with the intent to kill Lincoln,

00:06:42.289 --> 00:06:44.865
he pretty much just goes
up to Lincoln's box,

00:06:44.865 --> 00:06:46.280
and everyone knows who he is,

00:06:46.280 --> 00:06:48.433
and they say hi John,
and he just walks on by,

00:06:48.433 --> 00:06:49.880
walks right into Lincoln's box,

00:06:49.880 --> 00:06:51.861
shuts the door behind him,

00:06:51.861 --> 00:06:54.576
and shoots Lincoln through
the back of the head.

00:06:54.576 --> 00:06:58.101
At that point, he jumped on
the stage from the booth,

00:06:58.101 --> 00:07:01.892
which is maybe 14 feet above the stage.

00:07:01.892 --> 00:07:03.677
If you've never been to Ford's Theater

00:07:03.677 --> 00:07:06.326
and you have an opportunity,
I highly recommend you go,

00:07:06.326 --> 00:07:09.806
it's a really interesting
museum and historical place,

00:07:09.806 --> 00:07:11.923
and in the process, he
actually breaks his ankle,

00:07:11.923 --> 00:07:14.891
so in his running away he's dealing with

00:07:14.891 --> 00:07:18.235
this broken ankle and
eventually he is captured,

00:07:18.235 --> 00:07:21.902
and refuses to be taken
alive, so he is killed.

00:07:21.902 --> 00:07:25.462
And later the rest of the
conspirators are hanged

00:07:25.462 --> 00:07:28.216
for their participation in this plot.

00:07:28.216 --> 00:07:30.801
There's some confusion
over what Booth said

00:07:30.801 --> 00:07:33.556
when he jumped out of the box.

00:07:33.556 --> 00:07:37.723
A lot of people say that he
yelled sic semper tyrannis,

00:07:39.133 --> 00:07:42.839
which means, thus always to tyrants,

00:07:42.839 --> 00:07:46.756
and is also the motto of
the state of Virginia.

00:07:47.637 --> 00:07:50.166
Other people heard him say
things like I've done it,

00:07:50.166 --> 00:07:54.076
or revenge for the south,
but sic semper tyrannis

00:07:54.076 --> 00:07:57.181
is kind of the famous phrase
that has come out of this.

00:07:57.181 --> 00:07:59.367
So Booth is calling Lincoln a tyrant,

00:07:59.367 --> 00:08:02.457
and tyrants are eventually
always assassinated.

00:08:02.457 --> 00:08:04.870
The rest of the assassination plot

00:08:04.870 --> 00:08:07.691
from that evening mostly failed.

00:08:07.691 --> 00:08:10.111
One of the conspirators, Lewis Powell,

00:08:10.111 --> 00:08:12.992
did manage to get in to
William Seward's house

00:08:12.992 --> 00:08:16.427
and stab him, he did not
succeed in killing him,

00:08:16.427 --> 00:08:19.239
but he did wound Seward very badly.

00:08:19.239 --> 00:08:21.543
The rest of the assassination plots

00:08:21.543 --> 00:08:23.815
did not come to fruition whatsoever.

00:08:23.815 --> 00:08:26.626
One thing you'll notice
is that only a few parts

00:08:26.626 --> 00:08:29.204
of the Confederate Army
have actually surrendered

00:08:29.204 --> 00:08:31.404
at the time of Lincoln's assassination.

00:08:31.404 --> 00:08:33.802
So the war is, in some
cases, still ongoing,

00:08:33.802 --> 00:08:38.207
particularly in North Carolina,
in Raleigh and Durham,

00:08:38.207 --> 00:08:41.788
where Sherman's forces have come up

00:08:41.788 --> 00:08:43.599
through South Carolina and North Carolina

00:08:43.599 --> 00:08:47.311
to meet the forces of
Confederate General Joe Johnston.

00:08:47.311 --> 00:08:49.567
And it's on April the
26th that Joe Johnston

00:08:49.567 --> 00:08:52.841
surrenders to William Tecumseh Sherman.

00:08:52.841 --> 00:08:55.186
From that point forward, there
are a few dribs and drabs

00:08:55.186 --> 00:08:58.853
of other armies that
are still surrendering.

00:08:59.868 --> 00:09:04.035
Interesting fact, the last
Confederate unit to surrender

00:09:04.887 --> 00:09:08.319
actually surrendered in November of 1865,

00:09:08.319 --> 00:09:10.873
in Liverpool, England,
this was a Confederate ship

00:09:10.873 --> 00:09:12.525
that had been sailing around,

00:09:12.525 --> 00:09:14.205
and when they finally came into port,

00:09:14.205 --> 00:09:15.794
they officially surrendered.

00:09:15.794 --> 00:09:17.491
Now after Lincoln's assassination,

00:09:17.491 --> 00:09:20.586
which was an incredible
shock to the United States,

00:09:20.586 --> 00:09:22.721
remember that no President had ever

00:09:22.721 --> 00:09:24.670
been assassinated before,

00:09:24.670 --> 00:09:27.893
the power is then transferred
to Andrew Johnson,

00:09:27.893 --> 00:09:30.569
Lincoln's Vice-President.

00:09:30.569 --> 00:09:34.022
And Johnson's Presidency
is going to end up

00:09:34.022 --> 00:09:36.975
being very problematic
for a number of reasons,

00:09:36.975 --> 00:09:39.229
the most important of which being that

00:09:39.229 --> 00:09:40.990
he's very sympathetic to the south.

00:09:40.990 --> 00:09:43.502
With Johnson in power as President,

00:09:43.502 --> 00:09:46.612
he's going to have a
considerable amount of conflict

00:09:46.612 --> 00:09:49.858
with the American Congress,
which is dominated

00:09:49.858 --> 00:09:53.628
by radical Republicans who
think that Lincoln himself

00:09:53.628 --> 00:09:57.245
was not nearly punitive
enough toward the south.

00:09:57.245 --> 00:10:00.487
There's going to be just an
incredible battle of wills

00:10:00.487 --> 00:10:03.381
between Congress and
Johnson that's going to end

00:10:03.381 --> 00:10:06.095
with Johnson being the
first American President

00:10:06.095 --> 00:10:07.884
to be impeached.

00:10:07.884 --> 00:10:11.857
And so thus endeth the Civil
War of the United States,

00:10:11.857 --> 00:10:14.248
with the north victorious.

00:10:14.248 --> 00:10:17.612
The southern states come
back into the Union.

00:10:17.612 --> 00:10:19.951
The rebellion in the south is defeated,

00:10:19.951 --> 00:10:24.538
slavery has ended, and the
era of states rights is over.

00:10:24.538 --> 00:10:26.043
In the next video I'd like to talk,

00:10:26.043 --> 00:10:27.320
just for a few moments,

00:10:27.320 --> 00:10:31.013
about the big takeaways
about the American Civil War.

00:10:31.013 --> 00:10:32.885
What is is that makes it so important?

00:10:32.885 --> 00:10:34.672
And what were the lasting effects?

00:10:34.672 --> 00:10:37.523
I'll get to that in the next video.


Later stages of the Civil War part 2

WEBVTT
Kind: captions
Language: en

00:00:00.364 --> 00:00:01.789
- All right so we've been talking about

00:00:01.789 --> 00:00:03.800
the later stages of the Civil War.

00:00:03.800 --> 00:00:06.222
And in the last video we
just did a brief overview

00:00:06.222 --> 00:00:08.534
of the end of 1863

00:00:08.534 --> 00:00:11.745
after the north has won
the battle of Gettysburg

00:00:11.745 --> 00:00:16.095
and Lee has been turned
around and sent back down

00:00:16.095 --> 00:00:20.204
to Richmond where he will
be encamped for some time

00:00:20.204 --> 00:00:23.787
and Ulysses S. Grant
not only takes control

00:00:25.431 --> 00:00:28.834
of the Mississippi River with
the victory at Vicksburg,

00:00:28.834 --> 00:00:31.196
he also comes up into Tennessee,

00:00:31.196 --> 00:00:34.148
takes control of the state of Tennessee

00:00:34.148 --> 00:00:38.313
and in return Lincoln
makes him General in Chief

00:00:38.313 --> 00:00:40.242
of the Union armies.

00:00:40.242 --> 00:00:44.211
So now let's move on and talk about 1864

00:00:44.211 --> 00:00:48.653
and Sherman's March of the
Sea and the election of 1864.

00:00:48.653 --> 00:00:52.235
Both would be very important
to the United States victory.

00:00:52.235 --> 00:00:54.628
All right so let's take
a look at our map again.

00:00:54.628 --> 00:00:57.961
Now as we recall Lee is here in Richmond

00:01:00.306 --> 00:01:02.806
and Grant who was in Tennessee

00:01:03.930 --> 00:01:06.597
now coming over to challenge Lee

00:01:08.702 --> 00:01:10.844
at the siege of Richmond.

00:01:10.844 --> 00:01:13.785
So Grant has crossed over
from the Western theater

00:01:13.785 --> 00:01:16.401
of the war where he's been
pretty much the entire time

00:01:16.401 --> 00:01:18.133
into the Eastern theater

00:01:18.133 --> 00:01:20.787
and he's going for the killing blow now.

00:01:20.787 --> 00:01:25.013
You're remember that thanks
to the Anaconda strategy

00:01:25.013 --> 00:01:27.096
the union now has control

00:01:28.215 --> 00:01:30.798
of the entire area of the South

00:01:32.924 --> 00:01:34.753
through a blockade on this side,

00:01:34.753 --> 00:01:38.466
control of the Mississippi
and now control of Tennessee.

00:01:38.466 --> 00:01:41.094
So there's just this
litte area that's left.

00:01:41.094 --> 00:01:42.361
So now what happens?

00:01:42.361 --> 00:01:45.964
Well one of Grants generals who served

00:01:45.964 --> 00:01:49.793
under him in this Tennessee campaign

00:01:49.793 --> 00:01:52.115
is now going to turn his attention

00:01:52.115 --> 00:01:56.654
to a massive campaign of
total war in the south.

00:01:56.654 --> 00:01:59.120
So this is William Tecumseh Sherman

00:01:59.120 --> 00:02:02.537
and Sherman's idea is that he is going to

00:02:03.645 --> 00:02:06.062
cut a swath through the South

00:02:07.929 --> 00:02:12.096
and he is going to try to
destroy the South's morale

00:02:13.686 --> 00:02:17.353
by not only trying to
get rid of food stuffs

00:02:18.979 --> 00:02:21.715
and interrupt supply lines,

00:02:21.715 --> 00:02:24.715
destroy infrastructure, burn houses.

00:02:25.572 --> 00:02:28.873
He's gonna make things
so bad on the home front

00:02:28.873 --> 00:02:31.574
that the Confederate
soldiers who are fighting

00:02:31.574 --> 00:02:33.879
up here with Lee are gonna get upset

00:02:33.879 --> 00:02:36.372
that their property and their families

00:02:36.372 --> 00:02:38.086
are not being protected at home.

00:02:38.086 --> 00:02:41.834
So he's trying to win a morale victory

00:02:41.834 --> 00:02:44.814
by making people in the South really tired

00:02:44.814 --> 00:02:49.185
of being at war and also
by making Lee's soldiers

00:02:49.185 --> 00:02:51.156
want to desert and come back

00:02:51.156 --> 00:02:53.309
and defend their home territory.

00:02:53.309 --> 00:02:57.131
So Sherman turns his troops toward Atlanta

00:02:57.131 --> 00:02:59.131
and in September of 1864

00:03:01.173 --> 00:03:02.913
Sherman takes Atlanta.

00:03:02.913 --> 00:03:06.592
There's a very famous scene
of this in Gone with the Wind

00:03:06.592 --> 00:03:09.242
where you see Scarlet O'Hara looking out

00:03:09.242 --> 00:03:13.572
over the many injured people
in the city of Atlanta.

00:03:13.572 --> 00:03:15.725
That's Sherman's doing.

00:03:15.725 --> 00:03:17.824
But now let's turn attention away

00:03:17.824 --> 00:03:20.039
from the military campaigns for a second

00:03:20.039 --> 00:03:22.551
and talk about the politics of 1864.

00:03:22.551 --> 00:03:25.357
Now in 1864 it's an election year.

00:03:25.357 --> 00:03:26.737
It's been four years

00:03:26.737 --> 00:03:29.609
since Lincoln was elected
in November of 1860

00:03:29.609 --> 00:03:33.152
so now Lincoln has to
stand for reelection.

00:03:33.152 --> 00:03:34.961
And this is a really interesting election

00:03:34.961 --> 00:03:36.666
for lots of reasons.

00:03:36.666 --> 00:03:39.336
One is that it's the first election

00:03:39.336 --> 00:03:41.503
during wartime since 1812.

00:03:43.148 --> 00:03:45.132
So in the election of 1864

00:03:45.132 --> 00:03:47.455
soldiers are going to cast their ballots

00:03:47.455 --> 00:03:51.739
either by getting short
leaves to go to the ballot box

00:03:51.739 --> 00:03:54.432
or by sending in their ballots by mail.

00:03:54.432 --> 00:03:56.179
Another thing that's really
interesting about this

00:03:56.179 --> 00:03:59.085
is that Lincoln is not at all sure

00:03:59.085 --> 00:04:00.705
that he's going to win this election.

00:04:00.705 --> 00:04:03.515
In fact many in his own
party, the Republican Party,

00:04:03.515 --> 00:04:07.049
feel that he's been considerably
too soft on the south,

00:04:07.049 --> 00:04:09.360
that his plans for reunification

00:04:09.360 --> 00:04:11.676
are not nearly punitive enough.

00:04:11.676 --> 00:04:13.735
There are many who want to replace Lincoln

00:04:13.735 --> 00:04:16.818
with a more radical candidate in 1864

00:04:18.139 --> 00:04:20.403
but that does not end up happening.

00:04:20.403 --> 00:04:22.806
But one interesting thing
that does end up happening

00:04:22.806 --> 00:04:26.431
is to try to increase Lincoln's appeal

00:04:26.431 --> 00:04:29.664
his running mate is Andrew Johnson.

00:04:29.664 --> 00:04:32.263
Johnson was a slaveholder,

00:04:32.263 --> 00:04:34.952
believe it or not from Tennessee

00:04:34.952 --> 00:04:38.306
and the idea was that
maybe Johnson could pick up

00:04:38.306 --> 00:04:40.925
some of the Democrats
who might necessarily

00:04:40.925 --> 00:04:42.943
have voted for McClellan

00:04:42.943 --> 00:04:45.300
and maybe he could pick up
some of the border states

00:04:45.300 --> 00:04:46.839
the same way that we often might

00:04:46.839 --> 00:04:48.876
choose a vice president today

00:04:48.876 --> 00:04:51.036
because they come from
a crucial swing state.

00:04:51.036 --> 00:04:52.605
And this is gonna be important later

00:04:52.605 --> 00:04:54.974
because after Lincoln is assassinated

00:04:54.974 --> 00:04:57.361
Andrew Johnson will take over as president

00:04:57.361 --> 00:04:59.567
and he is quite a different president

00:04:59.567 --> 00:05:02.486
then Lincoln might have
been in the circumstances.

00:05:02.486 --> 00:05:04.262
Now on the Democratic side

00:05:04.262 --> 00:05:06.231
the candidate is George McClellan.

00:05:06.231 --> 00:05:09.109
You might remember
McClellan because he was one

00:05:09.109 --> 00:05:11.370
of the first commanders of the Union army

00:05:11.370 --> 00:05:15.149
and Lincoln sent him down for failing to

00:05:15.149 --> 00:05:17.495
really go after the enemy strongly

00:05:17.495 --> 00:05:19.326
in the early stages of the war.

00:05:19.326 --> 00:05:20.822
Now the Democratic Party is having

00:05:20.822 --> 00:05:22.689
some internal struggles at this point.

00:05:22.689 --> 00:05:24.406
There are some who think that the war

00:05:24.406 --> 00:05:26.427
against the South is very foolish,

00:05:26.427 --> 00:05:30.362
that no one should be fighting
in the north to end slavery

00:05:30.362 --> 00:05:34.176
which Lincoln has clearly
made a war goal by this point.

00:05:34.176 --> 00:05:36.677
So many just wish to have peace

00:05:36.677 --> 00:05:39.094
with the South on the terms of the South

00:05:39.094 --> 00:05:41.282
which is as a separate nation

00:05:41.282 --> 00:05:43.207
with the continuation of slavery.

00:05:43.207 --> 00:05:44.866
And then there are those Democrats

00:05:44.866 --> 00:05:47.088
who would like to continue the war

00:05:47.088 --> 00:05:49.818
and McClellan ends up being one of those.

00:05:49.818 --> 00:05:51.205
Obviously being a general,

00:05:51.205 --> 00:05:53.747
it would have been
pretty difficult for him

00:05:53.747 --> 00:05:55.483
to say that the war was pointless

00:05:55.483 --> 00:05:57.535
without having disappointed so many people

00:05:57.535 --> 00:05:59.615
who had fought for him or with him.

00:05:59.615 --> 00:06:01.133
This election is really crucial

00:06:01.133 --> 00:06:04.026
because many in the South are hoping

00:06:04.026 --> 00:06:07.209
that if someone other
than Lincoln gets elected,

00:06:07.209 --> 00:06:09.257
if the Democrats are elected,

00:06:09.257 --> 00:06:12.145
that is gonna be their last best hope

00:06:12.145 --> 00:06:16.398
to try to achieve their
independence from the union.

00:06:16.398 --> 00:06:19.884
If Lincoln is replaced by
someone who is pro-South,

00:06:19.884 --> 00:06:23.053
who is pro-slavery then perhaps
they'll just end the war

00:06:23.053 --> 00:06:24.270
and that would be the end of it.

00:06:24.270 --> 00:06:27.671
So whites the South are really holding on

00:06:27.671 --> 00:06:31.491
to the idea that Lincoln
will be defeated in 1864.

00:06:31.491 --> 00:06:33.388
And there are a lot of
reasons to think that Lincoln

00:06:33.388 --> 00:06:35.163
might have been defeated in this.

00:06:35.163 --> 00:06:37.642
Lincoln himself was not very sure

00:06:37.642 --> 00:06:39.522
that he will win this election.

00:06:39.522 --> 00:06:43.308
Remember that there has not
a single American president

00:06:43.308 --> 00:06:46.597
who has been reelected
in more than 30 years.

00:06:46.597 --> 00:06:48.356
The last president to be reelected

00:06:48.356 --> 00:06:51.417
was Andrew Jackson in 1832.

00:06:51.417 --> 00:06:56.234
So reelection is very a
unusual thing at this point

00:06:56.234 --> 00:06:58.808
and McClellan was a very popular general.

00:06:58.808 --> 00:07:01.622
He got popular because he was very keen

00:07:01.622 --> 00:07:03.701
to spare the lives of his soldiers

00:07:03.701 --> 00:07:06.044
which is quite different
from the approach that

00:07:06.044 --> 00:07:07.864
Ulysses S. Grant will end up taking

00:07:07.864 --> 00:07:09.458
at the end of the war.

00:07:09.458 --> 00:07:11.722
But there are several things
that go in Lincolns' favor.

00:07:11.722 --> 00:07:16.204
One is the capture of Atlanta
by Sherman in September

00:07:16.204 --> 00:07:19.477
and some very good military victories

00:07:19.477 --> 00:07:22.375
also in this eastern theater of the war.

00:07:22.375 --> 00:07:25.663
So McClellan who had hoped
that the war was going badly

00:07:25.663 --> 00:07:27.240
didn't have much on his side

00:07:27.240 --> 00:07:29.077
when it actually came to election day

00:07:29.077 --> 00:07:31.354
'cause at that point the
war was going pretty well.

00:07:31.354 --> 00:07:33.291
Remember that Sherman is here in Atlanta

00:07:33.291 --> 00:07:36.054
and Sherman is now going to pick up

00:07:36.054 --> 00:07:39.212
what is known as his March to the Sea

00:07:39.212 --> 00:07:41.962
when he cuts a 60 mile wide swath

00:07:43.357 --> 00:07:46.109
of destruction through Georgia.

00:07:46.109 --> 00:07:47.473
So things are looking pretty good

00:07:47.473 --> 00:07:49.418
for the United States at this point.

00:07:49.418 --> 00:07:52.018
And the turning point for
Lincoln in this election

00:07:52.018 --> 00:07:53.982
is really the votes of the soldiers

00:07:53.982 --> 00:07:57.382
and they have a really
strong pro-Lincoln mandate.

00:07:57.382 --> 00:07:59.049
One of Lincoln's campaign slogan

00:07:59.049 --> 00:08:01.042
is Vote As You Shot.

00:08:01.042 --> 00:08:03.767
So Lincoln ends up trouncing McClellan

00:08:03.767 --> 00:08:06.392
in the election of 1864

00:08:06.392 --> 00:08:10.027
and he really comes away
with a strong mandate

00:08:10.027 --> 00:08:12.116
to finish the war,

00:08:12.116 --> 00:08:15.631
finish it with an unconditional
surrender of the South

00:08:15.631 --> 00:08:17.255
and the end of slavery.

00:08:17.255 --> 00:08:20.341
And having triumpthed
in the election of 1864

00:08:20.341 --> 00:08:23.239
Lincoln it gets even more
good news from Georgia

00:08:23.239 --> 00:08:26.572
which is a telegram from General Sherman

00:08:28.505 --> 00:08:31.114
from the city of Savannah

00:08:31.114 --> 00:08:32.506
saying Mr. President,

00:08:32.506 --> 00:08:34.898
I wish to offer you the city of Savannah

00:08:34.898 --> 00:08:36.711
as a Christmas present.

00:08:36.711 --> 00:08:38.628
So in December 25, 1864

00:08:39.992 --> 00:08:42.342
Sherman's March to the Sea has concluded.

00:08:42.342 --> 00:08:46.809
And from there he's going
to start heading north.

00:08:46.809 --> 00:08:48.923
And we'll get to that in the next video.