Sal Khan on how you can support Khan Academy

WEBVTT
Kind: captions
Language: en

00:00:00.583 --> 00:00:02.928
Hi, this is Sal Khan,
founder of the Khan Academy,

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and I'm just here to
remind everyone watching

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that Khan Academy is a
not-for-profit organization,

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which means no one owns Khan Academy,

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we are a public charity,

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and we are dependent on donations.

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And donations from folks like you

00:00:17.112 --> 00:00:19.295
are what allow us to create the content

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and the interactive software

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that you and folks like you use.

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So I encourage you to
think of making a donation,

00:00:26.794 --> 00:00:29.348
even a few dollars from
everyone watching this video

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would cover Khan Academy's
costs for the coming year.

00:00:32.646 --> 00:00:34.457
We're a small team here at Khan Academy,

00:00:34.457 --> 00:00:36.483
under 100 folks, and
we're literally reaching

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tens of millions of people every month.

00:00:39.039 --> 00:00:42.266
So the social return on an
investment here is quite high.

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So, once again, really
encourage you to consider

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donating even a few dollars.

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Thank you.


Combining like terms with distribution

WEBVTT
Kind: captions
Language: en

00:00:00.384 --> 00:00:01.684
- [Voiceover] So I have
an expression here.

00:00:01.684 --> 00:00:05.251
Three times the entire
expression 5x plus six,

00:00:05.251 --> 00:00:08.784
and then plus the expression 7x plus two

00:00:08.784 --> 00:00:10.752
and all of that times four.

00:00:10.752 --> 00:00:12.317
And what I encourage you
to do is pause this video

00:00:12.317 --> 00:00:14.852
and see if you can
simplify this expression.

00:00:14.852 --> 00:00:15.584
And I'll give you a hint.

00:00:15.584 --> 00:00:17.518
You're gonna have to do some distribution

00:00:17.518 --> 00:00:20.484
and then some combining of like terms.

00:00:20.484 --> 00:00:22.250
All right, now I'm assuming
you've had a go at it.

00:00:22.250 --> 00:00:23.951
Now let's work through this together.

00:00:23.951 --> 00:00:26.684
So as I mentioned, when
I see this three times

00:00:26.684 --> 00:00:28.517
the entire expression 5x plus six,

00:00:28.517 --> 00:00:30.517
I want to distribute that three.

00:00:30.517 --> 00:00:32.618
So I want to multiply that three times 5x

00:00:32.618 --> 00:00:35.018
and that three times the six.

00:00:35.018 --> 00:00:37.317
So three times 5x, well if I have five Xs

00:00:37.317 --> 00:00:40.067
and I have three times
that, I'm gonna have 15 Xs.

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And then three times six is 18.

00:00:45.218 --> 00:00:49.018
So this part of the expression
we have now simplified

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to 15x plus 18.

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Now let's do the next part.

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So here I have this larger
expression written before

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this four but I wanna do the same thing.

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I just wanna distribute the four.

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It doesn't matter whether I'm multiplying,

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if I have the three or if I
have the number on the left side

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or the right side, so
let's distribute this four.

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I wanna do four times 7x and
I wanna do four times two.

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Four times 7x, well
that's going to be 28x,

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28x.

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And then four times two
is going to be eight.

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So we're almost there.

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This part of our expression has
simplified to 28x plus eight

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and now we can combine similar terms.

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So we have 15 Xs,

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and then we can add that to 28 Xs.

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Let me do this in a different color.

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If I have 15 of something
and I add 28 of something

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of that same something to it,

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well then I'm gonna have what, 43 Xs.

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So 43 Xs.

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15x plus 28 Xs, I added
the coefficients there,

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that's gonna be 43 Xs.

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And then 18 plus eight.

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Hey, let me do this in a new color.

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So 18 plus eight is going to be 26.

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And we're done.

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We've simplified this longer expression.

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We did some distribution then we combined

00:02:12.186 --> 00:02:16.401
some terms to get 43x plus 26.


Michelson–Morley Experiment introduction

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:02.385
- [Voiceover] We've seen
in several videos so far

00:00:02.385 --> 00:00:06.751
that most of the waves that
humans have encountered

00:00:06.751 --> 00:00:09.886
in nature--waves in
the water, sound waves,

00:00:09.886 --> 00:00:12.286
or just waves traveling along a rope--

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they were disturbances
traveling through a medium.

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And so when light displays
or has wave-like properties

00:00:19.566 --> 00:00:21.239
a very natural assumption

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was, well, light must
also be a disturbance

00:00:23.989 --> 00:00:26.184
traveling through some type of a medium

00:00:26.184 --> 00:00:29.314
even if that medium
wasn't so easy to detect.

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But they conjectured that
there is some type of medium

00:00:32.194 --> 00:00:34.090
that light is disturbance
traveling through.

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They called it the luminiferous ether.

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And much of physics in the 19th century

00:00:38.800 --> 00:00:42.821
was all around proving that
the luminiferous ether existed

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and also figuring out what
our relative velocity was

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in regards to that luminiferous ether.

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And why do we feel confident,

00:00:52.218 --> 00:00:53.751
or why did they feel confident,

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that there was a relative velocity?

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Well, we talked about
that in the last video.

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The earth is spinning and
then it's spinning around,

00:01:02.131 --> 00:01:04.288
it's orbiting around,
the sun at a nice clip

00:01:04.288 --> 00:01:06.289
and then the whole
solar system is orbiting

00:01:06.289 --> 00:01:08.391
around the center of the
galaxy at a nice clip.

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The galaxy itself might be moving,

00:01:10.527 --> 00:01:12.791
so if you have some
absolute frame of reference

00:01:12.791 --> 00:01:14.753
that's defined by the ether,

00:01:14.753 --> 00:01:18.667
well we are going to be
moving relative to it.

00:01:18.667 --> 00:01:20.815
And if we're moving relative to it

00:01:20.815 --> 00:01:22.752
well maybe you just
measure the speed of light

00:01:22.752 --> 00:01:26.501
in different directions and
see whether the speed of light

00:01:26.501 --> 00:01:28.257
is faster or slower in a certain direction

00:01:28.257 --> 00:01:30.105
and then that might help you identify--

00:01:30.105 --> 00:01:32.692
well, one, validate
that the ether exists--

00:01:32.692 --> 00:01:35.791
but also think about what our velocity is

00:01:35.791 --> 00:01:38.125
relative to the ether,

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relative to that absolute
frame of reference.

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But the problem in the 19th century

00:01:43.027 --> 00:01:44.852
is that we didn't have any precise way

00:01:44.852 --> 00:01:48.985
of actually measuring--or
a precise enough way

00:01:48.985 --> 00:01:51.586
of measuring--the speed of
light where we could detect

00:01:51.586 --> 00:01:54.419
the relative difference
due to the light going

00:01:54.419 --> 00:01:58.567
for or against, or into or away from,

00:01:58.567 --> 00:02:01.983
the actual direction of the ether wind.

00:02:01.983 --> 00:02:04.792
And so the experiment
that is usually cited

00:02:04.792 --> 00:02:06.987
with first kind of breaking things open,

00:02:06.987 --> 00:02:10.679
starting to really make
a dent in this whole idea

00:02:10.679 --> 00:02:15.679
of a luminiferous ether, is the
Michelson-Morley Experiment.

00:02:15.765 --> 00:02:17.901
Michelson-Morley Experiment.

00:02:17.901 --> 00:02:20.489
They recognized, okay, we can't
measure the speed of light

00:02:20.489 --> 00:02:23.217
with enough precision to detect
has it gotten slowed down

00:02:23.217 --> 00:02:26.724
by the ether wind or sped
up by the ether wind,

00:02:26.724 --> 00:02:27.951
but what we could do,

00:02:27.951 --> 00:02:29.953
and this is what Michelson
and Morley did do,

00:02:29.953 --> 00:02:33.088
and I'm gonna do an
oversimplification of the experiment,

00:02:33.088 --> 00:02:35.598
is that, okay, you have a light source,

00:02:35.598 --> 00:02:38.490
you have a light source right over here.

00:02:38.490 --> 00:02:41.241
So, you have a light source.

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And so that's going to send
light in this direction.

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It's going to send light just like that.

00:02:47.688 --> 00:02:50.590
And what you do is you
have a half-silvered mirror

00:02:50.590 --> 00:02:53.831
that allows half the light
to pass directly through it

00:02:53.831 --> 00:02:56.811
and half of it to be reflected.

00:02:56.811 --> 00:02:59.984
So let's put a half-silvered
mirror right over here.

00:02:59.984 --> 00:03:04.417
So, there's a half-silvered mirror.

00:03:04.417 --> 00:03:08.159
And so half of this light
will bounce off like this,

00:03:08.159 --> 00:03:10.361
and this is just a simplification of it.

00:03:10.361 --> 00:03:12.886
Let me do it a little neater than that.

00:03:12.886 --> 00:03:16.184
So half will bounce off like that.

00:03:16.184 --> 00:03:19.388
And then the other half will
be able to go through it.

00:03:19.388 --> 00:03:20.781
Will be able to go through it.

00:03:20.781 --> 00:03:22.887
It's a half-silvered mirror.

00:03:22.887 --> 00:03:25.889
And then we make each
of those light rays--

00:03:25.889 --> 00:03:28.048
we've essentially taken
our original light ray

00:03:28.048 --> 00:03:29.627
and split it into two--

00:03:29.627 --> 00:03:34.297
well then we'll then
bounce those off mirrors.

00:03:34.297 --> 00:03:36.848
Bounce those off mirrors
that are equidistant.

00:03:36.848 --> 00:03:37.893
And there are some adjustments

00:03:37.893 --> 00:03:39.089
when you actually have
to factor in everything,

00:03:39.089 --> 00:03:40.617
but just as a simple notion,

00:03:40.617 --> 00:03:43.259
these things are just
now going to bounce back.

00:03:43.259 --> 00:03:46.693
So, this one is now going to bounce back.

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It's half-silvered, it can go through,

00:03:49.154 --> 00:03:51.511
or part of it can go through, that mirror.

00:03:51.511 --> 00:03:52.823
So that's that ray.

00:03:52.823 --> 00:03:55.261
And then this one is going to bounce back.

00:03:55.261 --> 00:03:56.492
This one's going to go bounce back.

00:03:56.492 --> 00:04:00.509
And part of it is going to
bounce into this direction.

00:04:00.509 --> 00:04:02.927
And then you can detect what you see.

00:04:02.927 --> 00:04:05.450
You can detect what you see.

00:04:05.450 --> 00:04:08.949
So this right over here is a detector.

00:04:08.949 --> 00:04:09.820
And you might be saying

00:04:09.820 --> 00:04:11.224
okay, Sal, well what's the big deal?

00:04:11.224 --> 00:04:13.384
You've taken a light
source, you've bounced,

00:04:13.384 --> 00:04:16.054
you've split the light rays,
you've put them back together,

00:04:16.054 --> 00:04:17.923
you've bounced them around a little bit.

00:04:17.923 --> 00:04:21.994
But think about if there
was a luminiferous ether

00:04:21.994 --> 00:04:25.693
these light waves that are
going in orthogonal directions

00:04:25.693 --> 00:04:27.698
will be going at different velocities.

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Let's say if that luminiferous ether,

00:04:29.918 --> 00:04:34.337
if that luminiferous ether
wind was doing something

00:04:34.337 --> 00:04:36.551
like, let me see, if the ether wind

00:04:36.551 --> 00:04:39.511
were in this direction,

00:04:39.511 --> 00:04:42.588
if the ether wind were in that direction,

00:04:42.588 --> 00:04:45.525
when the light wave is going that way

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it should be going faster,
and when the light wave

00:04:48.184 --> 00:04:53.184
is coming back it should be going slower.

00:04:53.277 --> 00:04:55.350
And so what Michelson and
Morley did is they said

00:04:55.350 --> 00:04:58.319
okay, let's assume...

00:04:58.319 --> 00:05:01.074
let's adjust our
apparatus right over here,

00:05:01.074 --> 00:05:04.925
so when then these two
lights rays bounce off

00:05:04.925 --> 00:05:07.653
and come back together,
if there were no ether

00:05:07.653 --> 00:05:10.432
you would have some basic
interference pattern.

00:05:10.432 --> 00:05:12.420
So, what do I mean by
interference pattern?

00:05:12.420 --> 00:05:16.356
Well let's say that
you have maybe this one

00:05:16.356 --> 00:05:17.377
bouncing from up here.

00:05:17.377 --> 00:05:19.084
Let me do that in a different color.

00:05:19.084 --> 00:05:21.297
So the one bouncing from up here,

00:05:21.297 --> 00:05:26.237
the one bouncing from up here,

00:05:26.237 --> 00:05:29.396
let's say that looks like this.

00:05:29.396 --> 00:05:31.356
I'll just draw it as a longitudinal wave,

00:05:31.356 --> 00:05:32.981
just like this.

00:05:32.981 --> 00:05:35.257
Best I had in hand-drawn
longitudinal wave.

00:05:35.257 --> 00:05:39.348
And then the one coming
from the other direction,

00:05:39.348 --> 00:05:43.284
the one that bounces here,
and then comes back like this,

00:05:43.284 --> 00:05:47.727
is another longitudinal wave, like this.

00:05:47.727 --> 00:05:50.490
And when they overlap they
are going to interfere

00:05:50.490 --> 00:05:53.034
with each other, either
constructively interfere

00:05:53.034 --> 00:05:54.821
or destructively interfere.

00:05:54.821 --> 00:05:58.851
So you could have something like this.

00:05:58.851 --> 00:06:02.090
So let me copy and then let me paste it.

00:06:02.090 --> 00:06:04.818
So depending on how far or how fast

00:06:04.818 --> 00:06:06.466
each of these traveled,
you're going to have

00:06:06.466 --> 00:06:08.488
different levels of interference.

00:06:08.488 --> 00:06:10.056
And you would have a difference,

00:06:10.056 --> 00:06:11.391
depending on the orientation,

00:06:11.391 --> 00:06:13.957
depending on what the
actual ether wind is doing.

00:06:13.957 --> 00:06:16.685
But what Michelson and Morley observed

00:06:16.685 --> 00:06:19.378
is that no matter how they
oriented this apparatus,

00:06:19.378 --> 00:06:21.190
and they did it at
different times of the year,

00:06:21.190 --> 00:06:23.094
and they rotated it
around, and they rotated it

00:06:23.094 --> 00:06:26.177
in the vertical direction
and the horizontal direction,

00:06:26.177 --> 00:06:27.564
no matter what they did

00:06:27.564 --> 00:06:30.408
they always got the same
interference pattern.

00:06:30.408 --> 00:06:32.486
The interference pattern did not change.

00:06:32.486 --> 00:06:34.928
And because the interference
pattern did not change

00:06:34.928 --> 00:06:37.757
it implied that well, maybe this ether

00:06:37.757 --> 00:06:40.585
isn't really having an
effect on slowing down

00:06:40.585 --> 00:06:43.141
or speeding up the light waves.

00:06:43.141 --> 00:06:45.984
So this is often called
one of the most famous

00:06:45.984 --> 00:06:48.317
failed experiments in physics.

00:06:48.317 --> 00:06:50.367
So let me write this down.

00:06:50.367 --> 00:06:53.356
What's powerful about it is
that it was a failed experiment.

00:06:53.356 --> 00:06:55.457
Let me get my pen tool out.

00:06:55.457 --> 00:06:59.219
It was a failed, failed experiment

00:06:59.219 --> 00:07:00.878
but it made people start to question

00:07:00.878 --> 00:07:03.653
well, maybe there isn't an ether,

00:07:03.653 --> 00:07:06.954
a luminiferous ether, maybe
light just somehow travels

00:07:06.954 --> 00:07:08.421
through the vacuum.

00:07:08.421 --> 00:07:11.790
Maybe there is not this
absolute frame of reference

00:07:11.790 --> 00:07:15.152
that's defined by the luminiferous ether.

00:07:15.152 --> 00:07:17.653
And I wanna be clear, it wasn't
this experiment by itself.

00:07:17.653 --> 00:07:19.054
This experiment was one of many

00:07:19.054 --> 00:07:20.517
that started to put that doubt.

00:07:20.517 --> 00:07:22.084
But even after this experiment

00:07:22.084 --> 00:07:24.748
and they saw that there was no change

00:07:24.748 --> 00:07:26.156
in the interference pattern no matter how

00:07:26.156 --> 00:07:27.955
they oriented this thing,
whether is was going

00:07:27.955 --> 00:07:32.124
in the direction of the
hypothetical luminiferous ether

00:07:32.124 --> 00:07:33.368
or away from it, whatever,

00:07:33.368 --> 00:07:34.984
when they say no matter
how they oriented it

00:07:34.984 --> 00:07:36.528
they got the same interference patterns,

00:07:36.528 --> 00:07:38.293
people tried to come up
with other explanations

00:07:38.293 --> 00:07:41.915
that still might have been
okay with a Luminiferous Ether.

00:07:41.915 --> 00:07:43.552
Maybe the length got contracted

00:07:43.552 --> 00:07:45.216
in the direction of the motion.

00:07:45.216 --> 00:07:47.213
Maybe other things got affected.

00:07:47.213 --> 00:07:49.919
But this is a super important
experiment in physics

00:07:49.919 --> 00:07:53.396
because, once again, it started to show

00:07:53.396 --> 00:07:56.883
that hey, maybe there is
no luminiferous ether,

00:07:56.883 --> 00:07:58.892
that light is just gonna
go through that vacuum

00:07:58.892 --> 00:08:01.295
and, as we'll see, is
going to be traveling

00:08:01.295 --> 00:08:04.360
at the same velocity no matter what

00:08:04.360 --> 00:08:06.821
frame of reference you look at it from.

00:08:06.821 --> 00:08:09.892
But we'll explore that
more in future videos.


Potential ways to detect an ether wind

WEBVTT
Kind: captions
Language: en

00:00:00.542 --> 00:00:02.484
- [Voiceover] We've already
talked about light having

00:00:02.484 --> 00:00:05.318
wave-like properties, and the
waves that we're familiar with

00:00:05.318 --> 00:00:06.952
in our everyday life we consider to be

00:00:06.952 --> 00:00:09.718
disturbances traveling through a medium.

00:00:09.718 --> 00:00:12.118
We talked about dropping
a pebble in water,

00:00:12.118 --> 00:00:13.117
and the water's a medium,

00:00:13.117 --> 00:00:15.617
and we see the wave travel outwards.

00:00:15.617 --> 00:00:19.118
We think about sound waves,
which is disturbance in the air.

00:00:19.118 --> 00:00:22.385
We think about a wave
traveling through this rope,

00:00:22.385 --> 00:00:24.217
the medium there is the rope.

00:00:24.217 --> 00:00:27.151
So, in the mid-19th century it
was completely reasonable for

00:00:27.151 --> 00:00:30.751
folks to say, "Well look,
light has wave-like properties;

00:00:30.751 --> 00:00:33.652
it must be a disturbance
traveling through a medium."

00:00:33.652 --> 00:00:35.651
And they said, "Well what
do we call that medium,

00:00:35.651 --> 00:00:37.717
even though we don't observe it directly?

00:00:37.717 --> 00:00:40.618
Well, let's call it the
luminiferous Ether."

00:00:40.618 --> 00:00:43.217
So an obvious question
that was facing folks

00:00:43.217 --> 00:00:44.985
who had this reasonable
assumption, they said

00:00:44.985 --> 00:00:48.684
"Well, can we somehow detect
the luminiferous Ether?

00:00:48.684 --> 00:00:52.518
Can we validate the
luminiferous Ether existing?"

00:00:52.518 --> 00:00:55.685
And a key realization is,
is "Well, we must be moving

00:00:55.685 --> 00:00:59.417
quite rapidly relative to
the luminiferous Ether."

00:00:59.417 --> 00:01:01.112
How do we know that?

00:01:01.112 --> 00:01:04.051
Well, we just have to remind
ourselves that, obviously

00:01:04.051 --> 00:01:06.491
the Earth is rotating, but
not only is it rotating

00:01:06.491 --> 00:01:10.351
on its own axis, but it's
rotating around the sun.

00:01:10.351 --> 00:01:15.351
So if this is the sun right
over here, this is the Earth.

00:01:16.651 --> 00:01:20.150
The Earth is rotating, and
these are all rough figures,

00:01:20.150 --> 00:01:25.150
the Earth is moving around
the Sun at approximately

00:01:25.151 --> 00:01:30.151
30 kilometers per second.
30 kilometers per second!

00:01:30.751 --> 00:01:32.818
By our everyday standards,
that's quite fast,

00:01:32.818 --> 00:01:34.084
but we're not done yet.

00:01:34.084 --> 00:01:38.784
'Cuz the Sun is also moving
around the center of the galaxy.

00:01:38.784 --> 00:01:40.684
And this isn't an actual
picture of the Milky Way;

00:01:40.684 --> 00:01:43.118
obviously we haven't gotten
this far from our own galaxy

00:01:43.118 --> 00:01:45.353
to actually get this
type of a vantage point,

00:01:45.353 --> 00:01:49.418
but if the Sun were right
over there, the Sun,

00:01:49.418 --> 00:01:54.418
estimates are, are moving with
a speed of 200, roughly, 200,

00:01:56.538 --> 00:01:58.341
let me write that in a better color so

00:01:58.341 --> 00:02:02.484
you can actually see it,
200 kilometers per second.

00:02:02.484 --> 00:02:05.386
200 kilometers per second

00:02:05.386 --> 00:02:08.318
around the center of the Milky Way,

00:02:08.318 --> 00:02:11.527
and then the Milky Way
itself could be moving.

00:02:11.527 --> 00:02:16.171
So we don't know our actual,
kind of, our orientation

00:02:16.171 --> 00:02:18.651
relative to the Ether, but we are,

00:02:18.651 --> 00:02:20.551
we're constantly changing our orientation,

00:02:20.551 --> 00:02:22.518
we're moving in these orbital patterns.

00:02:22.518 --> 00:02:26.252
If there is some type
of luminiferous Ether,

00:02:26.252 --> 00:02:28.951
if there is some type
of luminiferous Ether,

00:02:28.951 --> 00:02:31.884
and I'm just gonna draw
these lines over here

00:02:31.884 --> 00:02:34.153
to kind of show our luminiferous Ether,

00:02:34.153 --> 00:02:36.690
we must be moving relative to it

00:02:36.690 --> 00:02:39.084
if we orient ourselves just the right way.

00:02:39.084 --> 00:02:41.752
In fact, the odds of us
being stationary relative to

00:02:41.752 --> 00:02:44.052
the Ether are pretty close to zero,

00:02:44.052 --> 00:02:45.291
especially if we wait a little.

00:02:45.291 --> 00:02:47.884
If we're stationary relative
to the Ether right now,

00:02:47.884 --> 00:02:50.832
let's say at this point, since
we're changing our direction,

00:02:50.832 --> 00:02:52.350
we're not going to be
stationary relative to

00:02:52.350 --> 00:02:54.051
the Ether at that point.

00:02:54.051 --> 00:02:55.165
And that's just when you consider

00:02:55.165 --> 00:02:56.884
the Earth's orbit around the Sun.

00:02:56.884 --> 00:02:58.719
It's even more true
when you think about the

00:02:58.719 --> 00:03:02.184
solar system's orbit around
the center of the galaxy,

00:03:02.184 --> 00:03:03.751
or even the movement of the galaxy.

00:03:03.751 --> 00:03:07.011
So, we should be moving
relative to the Ether,

00:03:07.011 --> 00:03:10.517
or the Ether should be
moving relative to us.

00:03:10.517 --> 00:03:13.355
So we should be able
to detect some type of,

00:03:13.355 --> 00:03:16.184
some type of what's
called an "Ether wind".

00:03:16.184 --> 00:03:18.750
'Cuz it should be moving relative...

00:03:18.750 --> 00:03:21.485
Ether wind.

00:03:21.485 --> 00:03:23.518
Now how would you detect an Ether wind?

00:03:23.518 --> 00:03:25.985
Well, let's think about
some other type of medium

00:03:25.985 --> 00:03:27.717
moving relative to us.

00:03:27.717 --> 00:03:32.717
Let's say that we are
sitting on an island,

00:03:34.847 --> 00:03:37.818
let me do this in a better
color for an island.

00:03:37.818 --> 00:03:39.451
So let's say that we're
on an island that's in

00:03:39.451 --> 00:03:41.117
the middle of a stream.

00:03:41.117 --> 00:03:43.984
So these are the shores of the stream.

00:03:43.984 --> 00:03:45.951
These are the shores of the stream.

00:03:45.951 --> 00:03:48.119
And there is some type of a current.

00:03:48.119 --> 00:03:52.617
So the water is moving in that direction.

00:03:52.617 --> 00:03:55.219
So that's the medium.

00:03:55.219 --> 00:03:58.151
And now let's start a wave
propagating through this.

00:03:58.151 --> 00:04:01.084
So if I were to just
take a pebble and drop it

00:04:01.084 --> 00:04:04.185
right over here, what would happen?

00:04:04.185 --> 00:04:06.950
Well the wave is going to
propagate faster to the left

00:04:06.950 --> 00:04:09.317
than it is to the right.

00:04:09.317 --> 00:04:10.751
This is from our everyday experience,

00:04:10.751 --> 00:04:13.085
and that's because to
the left it's moving,

00:04:13.085 --> 00:04:15.617
the medium is also moving to the left.

00:04:15.617 --> 00:04:17.717
So as the medium moves,

00:04:17.717 --> 00:04:19.484
and then you propagate
through that medium,

00:04:19.484 --> 00:04:21.484
you're going to move faster
to the left than to the right.

00:04:21.484 --> 00:04:25.017
So the wave is going to
propagate, is going to propagate,

00:04:25.017 --> 00:04:27.951
something is going to propagate,

00:04:27.951 --> 00:04:30.384
so after a small period of time,

00:04:30.384 --> 00:04:31.886
the crest on the right might be there,

00:04:31.886 --> 00:04:33.585
but the crest on the left might be there.

00:04:33.585 --> 00:04:37.017
So it might look something like this.

00:04:37.017 --> 00:04:39.018
And then after another period of time,

00:04:39.018 --> 00:04:43.586
it might look something, it'll
look something like this.

00:04:43.586 --> 00:04:46.084
So the general point is, for
this little stream example,

00:04:46.084 --> 00:04:48.684
you're going to see your
wave propagate faster

00:04:48.684 --> 00:04:51.750
in the direction of which
the medium is moving.

00:04:51.750 --> 00:04:55.584
So similarly, if you have an Ether wind,

00:04:55.584 --> 00:04:58.817
if you have Ether wind and
this luminiferous Ether

00:04:58.817 --> 00:05:01.892
is the medium by which
the light propagates,

00:05:01.892 --> 00:05:05.431
the light is a disturbance in this medium,

00:05:05.431 --> 00:05:08.377
then if this Ether wind has some,

00:05:08.377 --> 00:05:10.804
let's say it has some speed,

00:05:10.804 --> 00:05:12.317
let's just call it "S".

00:05:12.317 --> 00:05:17.317
If you were try to propagate
light in that direction

00:05:20.084 --> 00:05:25.084
versus in this direction,
versus in that direction,

00:05:25.251 --> 00:05:28.384
it should go faster, we
should notice it going faster

00:05:28.384 --> 00:05:30.951
if it's going along the
same direction as the Ether.

00:05:30.951 --> 00:05:32.285
'Cuz it's propagating through something

00:05:32.285 --> 00:05:35.118
that's also moving relative to us.

00:05:35.118 --> 00:05:37.951
And likewise, if it's going
in the opposite direction

00:05:37.951 --> 00:05:40.184
of the Ether, even though
it's propagating through

00:05:40.184 --> 00:05:42.185
the actual Ether at that same speed,

00:05:42.185 --> 00:05:45.052
the Ether is moving in the
other direction, so the light,

00:05:45.052 --> 00:05:48.371
based on our 19th century
understanding of the universe,

00:05:48.371 --> 00:05:50.385
the light should seem slower.

00:05:50.385 --> 00:05:52.051
So you can imagine, people
started to theorize,

00:05:52.051 --> 00:05:55.884
"Well, maybe we can measure
light in different directions

00:05:55.884 --> 00:05:59.718
and see if, relative to
us, if relative to us,

00:05:59.718 --> 00:06:02.351
we see a different velocity for light."

00:06:02.351 --> 00:06:05.751
Now the problem was, is that
in the mid-19th century,

00:06:05.751 --> 00:06:07.318
light is incredibly fast.

00:06:07.318 --> 00:06:10.250
We now know that the speed
of light is approximately

00:06:10.250 --> 00:06:15.250
300 thousand kilometers per second.

00:06:17.618 --> 00:06:20.585
And in the mid-19th century,
we didn't have good tools

00:06:20.585 --> 00:06:25.218
to measure this with a lot of accuracy.

00:06:25.218 --> 00:06:27.685
Especially because the Ether wind itself,

00:06:27.685 --> 00:06:29.984
even if you say "This is
30 kilometers per second,

00:06:29.984 --> 00:06:32.217
maybe we're moving around
the galaxy at, you know,

00:06:32.217 --> 00:06:35.519
200 kilometers per second, maybe
300 kilometers per second",

00:06:35.519 --> 00:06:39.784
that's still a small fraction
of the actual speed of light.

00:06:39.784 --> 00:06:43.384
So if you don't have a lot of
accuracy when you're measuring

00:06:43.384 --> 00:06:45.618
the speed of light in these
different directions, and

00:06:45.618 --> 00:06:48.485
the Ether wind is so slow
relative to the speed of light,

00:06:48.485 --> 00:06:51.484
well, with just traditional
tools in the 19th century,

00:06:51.484 --> 00:06:52.951
you're not going to be able to detect

00:06:52.951 --> 00:06:56.250
this actual Ether wind, if it existed.

00:06:56.250 --> 00:06:58.184
And that's what gets us to the famous

00:06:58.184 --> 00:07:00.118
Michelson-Morley Experiment,

00:07:00.118 --> 00:07:02.634
because there they didn't
just directly try to measure

00:07:02.634 --> 00:07:04.938
the speed of light in
one direction or another,

00:07:04.938 --> 00:07:09.517
instead they thought about,
"Let's split some light into

00:07:09.517 --> 00:07:12.018
two different directions,
and then recombine them

00:07:12.018 --> 00:07:13.884
and see the interference patterns.

00:07:13.884 --> 00:07:16.818
And if the different directions
traveled at different speeds

00:07:16.818 --> 00:07:19.118
then we'll have different
interference patterns."

00:07:19.118 --> 00:07:22.484
And we're going to see
that in the next video.


RutherfordÂs gold foil experiment

WEBVTT
Kind: captions
Language: en

00:00:00.329 --> 00:00:02.813
- [Voiceover] This is
a quote by a physicist

00:00:02.813 --> 00:00:05.617
as a comment on one of
his experimental results.

00:00:06.041 --> 00:00:08.223
He said, about his experiment, he said,

00:00:08.223 --> 00:00:10.917
"It was as if you fired a 15-inch shell

00:00:10.917 --> 00:00:13.000
"at a piece of tissue paper,

00:00:14.850 --> 00:00:16.586
"and it came back and hit you."

00:00:16.588 --> 00:00:20.266
So let's talk about his
experiment and what he was doing.

00:00:20.266 --> 00:00:24.410
Rutherford, at the time, had
been doing a lot of research

00:00:24.410 --> 00:00:26.216
on radioactivity.

00:00:27.359 --> 00:00:31.161
He was friends with Marie
Curie and her husband, Pierre.

00:00:32.212 --> 00:00:34.952
And he had done a lot of studies

00:00:34.952 --> 00:00:37.506
looking at the different
kinds of reactivity,

00:00:37.506 --> 00:00:41.308
and more specifically, he
was curious at this time

00:00:41.871 --> 00:00:45.338
about alpha particles,

00:00:46.978 --> 00:00:48.399
which are,

00:00:48.899 --> 00:00:50.308
actually, at the time, he didn't know

00:00:50.308 --> 00:00:52.712
what they were, but we now know they are

00:00:52.712 --> 00:00:55.706
Helium, 2+ nuclei.

00:00:55.706 --> 00:01:00.252
So that means we have two
protons in the nucleus,

00:01:00.252 --> 00:01:04.469
since it's Helium, and
it also has two neutrons.

00:01:05.333 --> 00:01:07.237
And it doesn't have any
electrons, and thus,

00:01:07.237 --> 00:01:09.275
it has a 2+ charge.

00:01:10.010 --> 00:01:13.228
So what Rutherford did,
he took a piece of radium

00:01:13.228 --> 00:01:15.660
and he put it inside a lead box.

00:01:17.593 --> 00:01:21.094
And the lead box had a
small hole in it on one side

00:01:21.610 --> 00:01:26.155
so that the radioactive alpha particles

00:01:27.438 --> 00:01:31.287
could come out of that hole in
the direction that he wanted.

00:01:32.499 --> 00:01:36.307
And then, he shot the alpha particles

00:01:36.307 --> 00:01:39.231
at a piece of gold foil,

00:01:39.747 --> 00:01:42.570
a very thin piece of gold foil.

00:01:45.362 --> 00:01:49.639
And he was curious to see if
he could learn a little bit

00:01:49.639 --> 00:01:52.692
about the structure of the
atom using this experiment.

00:01:52.692 --> 00:01:55.095
So, if we look back at our quote,

00:01:55.095 --> 00:01:59.571
we would say that our
alpha particles here,

00:02:00.041 --> 00:02:03.479
the alpha particles are the bullets

00:02:05.619 --> 00:02:09.790
that are coming out of our
alpha particle gun, and

00:02:13.350 --> 00:02:15.440
gold foil is our tissue paper.

00:02:16.816 --> 00:02:19.393
And we have these pretty fast and massive

00:02:19.393 --> 00:02:21.581
alpha particles that we're shooting at it.

00:02:21.581 --> 00:02:25.658
But why was Rutherford
expecting that to happen here?

00:02:25.658 --> 00:02:27.604
It's not necessarily straightforward,

00:02:27.604 --> 00:02:30.390
at least to me, why you would
think these alpha particles

00:02:30.390 --> 00:02:32.660
would just go straight
through the gold foil.

00:02:33.478 --> 00:02:37.315
So what Rutherford, at
the time, was doing was,

00:02:37.315 --> 00:02:40.671
he was testing the plum pudding model.

00:02:42.208 --> 00:02:46.132
So this is pretty early
in history, where we,

00:02:46.962 --> 00:02:49.546
we being scientists way back then,

00:02:49.546 --> 00:02:53.470
knew that J. J. Thomson,
another physicist,

00:02:53.470 --> 00:02:55.834
had just discovered electrons.

00:02:55.834 --> 00:02:57.940
So we knew the atom,

00:02:58.945 --> 00:03:03.143
the atom had these particles
in it that were small,

00:03:03.143 --> 00:03:05.766
that were really small,
we knew that they were

00:03:07.586 --> 00:03:11.775
less than one percent the
mass of a Hydrogen atom,

00:03:11.775 --> 00:03:14.422
so way smaller than an atom.

00:03:14.422 --> 00:03:16.149
And we knew they were negatively charged,

00:03:16.149 --> 00:03:17.719
so I'm going to call them electrons

00:03:17.719 --> 00:03:19.989
'cause we know they're electrons now.

00:03:20.297 --> 00:03:23.091
And so J. J. Thomson knew

00:03:23.091 --> 00:03:26.342
that electrons existed

00:03:26.342 --> 00:03:28.465
based on his experimental results,

00:03:28.465 --> 00:03:31.251
and he proposed, based on his results,

00:03:31.251 --> 00:03:35.297
that an atom looks something
like a plum pudding.

00:03:35.297 --> 00:03:37.781
And if you don't know
what a plum pudding is,

00:03:37.781 --> 00:03:39.824
because maybe you're not British,

00:03:39.824 --> 00:03:41.914
or maybe you just don't like dessert,

00:03:41.914 --> 00:03:44.329
you can also imagine it
looking something like

00:03:44.329 --> 00:03:46.316
a chocolate chip cookie.

00:03:46.316 --> 00:03:51.216
So we have these little
negatively-charged particles

00:03:51.471 --> 00:03:53.607
that are stuck inside the atom,

00:03:53.607 --> 00:03:57.090
but most of the atom is made up of

00:03:57.090 --> 00:04:00.475
a positively-charged soup.

00:04:02.190 --> 00:04:05.263
And this was mainly because

00:04:06.986 --> 00:04:10.530
the atom overall has to be neutral.

00:04:10.705 --> 00:04:12.957
Scientists knew that atoms were neutral,

00:04:12.957 --> 00:04:14.490
so there had to be something there

00:04:14.490 --> 00:04:17.996
to cancel out the negative
charge of the electron.

00:04:19.901 --> 00:04:23.451
So because Rutherford was starting

00:04:23.451 --> 00:04:25.447
with this in his mind

00:04:25.447 --> 00:04:29.361
for what the gold atoms looked like,

00:04:29.361 --> 00:04:32.061
he could actually do
mathematical predictions

00:04:32.061 --> 00:04:34.289
on what the alpha particles would do.

00:04:34.289 --> 00:04:35.891
And what he predicted was that

00:04:35.891 --> 00:04:38.533
they would just go straight through.

00:04:40.419 --> 00:04:45.011
You can use physics equations
to look at the electric field

00:04:45.574 --> 00:04:48.587
that's generated by this
positively-charged soup,

00:04:48.587 --> 00:04:51.118
and it turns out that the field,

00:04:51.118 --> 00:04:53.788
because the charge is spread
out all over the atom,

00:04:53.788 --> 00:04:55.739
the field is very weak.

00:04:55.739 --> 00:04:57.829
And so, what he thought would happen

00:04:57.829 --> 00:05:00.034
was that all the particles
would just go straight through

00:05:00.034 --> 00:05:04.227
and then, occasionally, one
might be bent a little bit.

00:05:04.748 --> 00:05:06.493
Since we do have

00:05:07.023 --> 00:05:10.254
a positively-charged soupy atom,

00:05:10.704 --> 00:05:14.569
depending on where the
alpha particle goes through,

00:05:14.569 --> 00:05:16.822
he thought you might see a
little bit of deflection,

00:05:16.822 --> 00:05:18.929
but mostly, they should
go straight through.

00:05:20.820 --> 00:05:23.095
And I guess we started with a spoiler,

00:05:23.095 --> 00:05:26.642
'cause we know that he didn't
quite get what he expected.

00:05:27.321 --> 00:05:29.916
So what exactly did Rutherford see?

00:05:30.897 --> 00:05:34.417
Well, he shot his alpha
particles at his tissue paper,

00:05:34.417 --> 00:05:39.057
and he saw most of the
particles go straight through,

00:05:40.082 --> 00:05:41.818
just as he expected.

00:05:42.567 --> 00:05:46.978
In fact, he saw almost all the particles

00:05:46.978 --> 00:05:48.279
go straight through.

00:05:48.279 --> 00:05:52.876
He saw a couple of them
be deflected a little bit,

00:05:52.876 --> 00:05:55.175
so they got deflected off their path

00:05:55.175 --> 00:05:57.450
maybe about one degree, so barely enough

00:05:57.450 --> 00:05:58.843
to be able to see it.

00:05:58.843 --> 00:06:03.173
And, if he had not been a curious chemist,

00:06:03.173 --> 00:06:05.664
we would maybe still think, right now,

00:06:05.664 --> 00:06:08.892
that this is what an atom looks like.

00:06:10.081 --> 00:06:14.348
But luckily, Rutherford was
a very thorough chemist,

00:06:14.679 --> 00:06:16.813
and he also thought,
it might be interesting

00:06:16.813 --> 00:06:20.506
to detect whether

00:06:21.389 --> 00:06:25.015
particles came, not just here,

00:06:25.015 --> 00:06:27.078
he didn't just put a detector screen here,

00:06:27.078 --> 00:06:30.746
he put a detector screen
that went all the way around.

00:06:34.183 --> 00:06:37.410
So, all the way around,
almost all the way around,

00:06:37.410 --> 00:06:40.322
giving enough space for the
alpha particles to go in.

00:06:40.962 --> 00:06:44.469
And he was being really careful here,

00:06:44.469 --> 00:06:46.605
'cause he didn't really
expect to see anything

00:06:46.605 --> 00:06:48.416
right around here or here or here,

00:06:48.416 --> 00:06:50.000
or really anywhere except for here.

00:06:50.000 --> 00:06:53.764
But it turned out that for every

00:06:54.324 --> 00:06:56.371
one in...

00:06:57.091 --> 00:06:59.556
one in 20,000

00:06:59.556 --> 00:07:00.689
alpha particles,

00:07:00.689 --> 00:07:03.262
or some crazy-tiny number like that,

00:07:04.038 --> 00:07:06.754
for every one in 20,000 alpha particles,

00:07:06.754 --> 00:07:09.703
he saw the particles hit the gold foil

00:07:09.703 --> 00:07:11.800
and bounce back.

00:07:12.087 --> 00:07:13.720
And that's crazy, right?

00:07:13.720 --> 00:07:15.252
That's exactly what you don't expect

00:07:15.252 --> 00:07:19.380
when you hit a piece of
tissue paper with a bullet.

00:07:20.012 --> 00:07:22.423
So the first thing he did, I think,

00:07:22.423 --> 00:07:25.051
was not go, hmmm, this is really crazy,

00:07:25.051 --> 00:07:27.303
we just won a Nobel Prize here.

00:07:27.303 --> 00:07:29.230
I'm pretty sure the
first thing he did was,

00:07:29.230 --> 00:07:30.600
this is weird.

00:07:30.600 --> 00:07:33.053
And then he probably checked
his experimental results.

00:07:33.053 --> 00:07:34.478
And he tried to repeat it,

00:07:34.478 --> 00:07:35.940
and he checked everything to make sure

00:07:35.940 --> 00:07:37.594
nothing was going wrong,

00:07:37.594 --> 00:07:41.108
and it turned out that, yes,

00:07:41.108 --> 00:07:42.813
something was actually happening.

00:07:42.813 --> 00:07:45.878
This one in 20,000 alpha
particles was real.

00:07:47.388 --> 00:07:48.567
So what did this mean?

00:07:48.567 --> 00:07:52.276
This meant that we needed
a new atomic model.

00:07:52.862 --> 00:07:56.090
We had to explain, somehow,
that a tiny fraction

00:07:56.090 --> 00:07:58.522
of the alpha particles
was getting bounced back.

00:07:59.387 --> 00:08:00.868
So how did he do this?

00:08:00.868 --> 00:08:03.190
He knew there was something in the atom

00:08:03.190 --> 00:08:05.213
that was tiny,

00:08:07.111 --> 00:08:10.722
massive, and positively charged.

00:08:13.133 --> 00:08:15.844
And he knew that it had to be tiny

00:08:15.844 --> 00:08:18.184
because not very many alpha particles

00:08:18.184 --> 00:08:19.949
interacted with it, 'cause most of them

00:08:19.949 --> 00:08:21.551
went straight through.

00:08:21.551 --> 00:08:23.060
He knew that it had to be massive

00:08:23.060 --> 00:08:26.799
and positively charged
because, well, the electrons

00:08:26.799 --> 00:08:30.212
are really small, and
most of the particles

00:08:30.212 --> 00:08:31.396
went straight through.

00:08:31.396 --> 00:08:34.391
So whatever these particles
were interacting with

00:08:34.391 --> 00:08:38.431
had to be very small but really heavy,

00:08:39.081 --> 00:08:41.328
which is how they bounced right back.

00:08:42.100 --> 00:08:43.952
So he made a new

00:08:45.699 --> 00:08:48.490
model of the atom that incorporated

00:08:48.490 --> 00:08:51.266
these requirements.

00:08:53.059 --> 00:08:56.617
And what he said was that

00:08:56.947 --> 00:09:00.670
there must be something in
there with these properties,

00:09:00.670 --> 00:09:03.293
which we now call the nucleus.

00:09:07.037 --> 00:09:08.727
And it's really tiny,

00:09:08.727 --> 00:09:11.782
in fact he was able to
calculate, not exactly.

00:09:11.782 --> 00:09:14.098
He was able to calculate
approximately how big it was

00:09:14.098 --> 00:09:16.564
based on how many alpha particles hit it,

00:09:16.564 --> 00:09:20.001
and he said it was approximately

00:09:20.001 --> 00:09:24.268
1/10,000

00:09:24.848 --> 00:09:27.111
of the volume of the atom.

00:09:28.342 --> 00:09:30.576
And then, what else do we have?

00:09:30.576 --> 00:09:32.991
We know we have this nucleus,
which is positively-charged

00:09:32.991 --> 00:09:34.732
and tiny and massive.

00:09:34.732 --> 00:09:37.142
And then we also have our electrons.

00:09:37.983 --> 00:09:40.514
And then what's the
rest of the atom doing?

00:09:40.514 --> 00:09:43.927
Based on all of this, that
means most of the atom

00:09:43.927 --> 00:09:46.104
is actually empty space.

00:09:49.151 --> 00:09:52.379
Since the electrons are really small

00:09:52.379 --> 00:09:55.536
and the nucleus only takes up

00:09:55.536 --> 00:09:58.647
1/10,000 of the radius,

00:09:58.647 --> 00:10:01.179
the rest of that space
is all just nothing,

00:10:01.179 --> 00:10:04.406
which is kind of crazy, so
based on this particular model

00:10:04.406 --> 00:10:08.067
that Rutherford made next,

00:10:08.067 --> 00:10:10.234
he was able to explain his results.

00:10:10.234 --> 00:10:14.646
He was able to explain that
most of the alpha particles

00:10:14.646 --> 00:10:18.528
just went straight through,
and then every now and then,

00:10:18.528 --> 00:10:23.255
an alpha particle would come
really close to the nucleus,

00:10:23.255 --> 00:10:26.092
and then that would get
defected a little bit,

00:10:26.092 --> 00:10:29.464
and even more rare, an
alpha particle may hit

00:10:29.464 --> 00:10:31.688
a nucleus straight on,
and then it would get

00:10:31.688 --> 00:10:34.062
bounced off because the
nucleus is super-heavy

00:10:34.062 --> 00:10:36.035
and because it is positively charged,

00:10:36.035 --> 00:10:39.153
so it would repel the
positively-charged alpha particle.

00:10:39.153 --> 00:10:41.820
Rutherford called this particular model,

00:10:41.820 --> 00:10:44.305
or we call it now, I'm
not sure which, actually,

00:10:44.305 --> 00:10:47.039
he called it the Nuclear Model.

00:10:50.319 --> 00:10:52.037
This actually looks pretty similar

00:10:52.037 --> 00:10:55.380
to the modern picture of the atom

00:10:55.380 --> 00:10:56.750
that most people think of.

00:10:56.750 --> 00:10:59.304
There's a lot of questions that
are still not answered here,

00:10:59.304 --> 00:11:01.923
like what exactly the electrons are doing.

00:11:02.671 --> 00:11:04.732
Or where are they?

00:11:06.642 --> 00:11:09.239
Where are the electrons?

00:11:10.914 --> 00:11:13.979
But because Rutherford
proposed this new model,

00:11:13.979 --> 00:11:16.463
other scientists were able
to design new expiriments

00:11:16.463 --> 00:11:17.740
to test it.

00:11:17.740 --> 00:11:20.875
And not very long afterward,
we had a pretty good picture

00:11:20.875 --> 00:11:22.152
of what was going on

00:11:22.152 --> 00:11:23.317
on the level of the atom.


Light and the luminiferous ether

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:03.063
- [Voiceover] So let's think
a little bit about waves.

00:00:03.063 --> 00:00:05.684
The classical notion of what a wave is,

00:00:05.684 --> 00:00:08.670
is it's a disturbance
traveling through a medium.

00:00:08.670 --> 00:00:13.670
Disturbance traveling through a medium.

00:00:18.768 --> 00:00:20.251
So what do we mean by disturbance and

00:00:20.251 --> 00:00:22.120
what do we mean by a medium?

00:00:22.120 --> 00:00:25.066
We could come up with some
fairly simple examples.

00:00:25.066 --> 00:00:29.007
Let's say that I have
a little puddle here.

00:00:29.007 --> 00:00:30.734
So that's my little puddle.

00:00:30.734 --> 00:00:34.127
And let's say I were to
drop a stone in that puddle.

00:00:34.127 --> 00:00:35.834
So this is my stone.

00:00:35.834 --> 00:00:37.358
It gets dropped in the puddle.

00:00:37.358 --> 00:00:38.963
We've all seen what happens.

00:00:38.963 --> 00:00:40.832
Right when it goes into the water,

00:00:40.832 --> 00:00:42.498
that pushes that water down,

00:00:42.498 --> 00:00:44.448
pushes the water around it out,

00:00:44.448 --> 00:00:46.196
then that water comes back up.

00:00:46.196 --> 00:00:49.060
Then you have this traveling disturbance.

00:00:49.060 --> 00:00:51.681
You have this traveling disturbance.

00:00:51.681 --> 00:00:54.993
These kind of rings that
start to radiate outward

00:00:54.993 --> 00:00:59.993
from where I actually dropped the pebble.

00:01:04.461 --> 00:01:09.215
You can actually see them move outwards.

00:01:09.215 --> 00:01:12.425
You can see the crests of
those waves move outwards.

00:01:12.425 --> 00:01:14.091
We're talking about a disturbance.

00:01:14.091 --> 00:01:15.229
Well this is that disturbance.

00:01:15.229 --> 00:01:17.484
The pond was completely flat,

00:01:17.484 --> 00:01:18.743
but then we agitate it.

00:01:18.743 --> 00:01:20.105
We pushed it down.

00:01:20.105 --> 00:01:21.324
It pushed the water outwards.

00:01:21.324 --> 00:01:23.799
Then that pushed the water
next to it up and down,

00:01:23.799 --> 00:01:24.937
up and down.

00:01:24.937 --> 00:01:27.558
It traveled outwards from the point

00:01:27.558 --> 00:01:29.204
of that initial disturbance.

00:01:29.204 --> 00:01:33.653
We have this disturbance
traveling through the medium.

00:01:33.653 --> 00:01:35.340
What's the medium here?

00:01:35.340 --> 00:01:38.184
The medium here is the water.

00:01:38.184 --> 00:01:41.130
The initial disturbance was the rock

00:01:41.130 --> 00:01:42.796
disturbing that water.

00:01:42.796 --> 00:01:44.909
But then that water disturbed
the water around it,

00:01:44.909 --> 00:01:46.433
which disturbed the water around it.

00:01:46.433 --> 00:01:49.826
That disturbance kept
traveling through the medium.

00:01:49.826 --> 00:01:52.711
We can give other examples of this.

00:01:52.711 --> 00:01:57.711
If I take a really long string
and hold it right there.

00:01:59.314 --> 00:02:01.041
That's my hand.

00:02:01.041 --> 00:02:05.287
The string is, let's just
say, attached to something.

00:02:05.287 --> 00:02:07.728
Let's say it's a really long string

00:02:07.728 --> 00:02:10.363
and right now there's some slack in it.

00:02:10.363 --> 00:02:13.025
It's attached to a wall.

00:02:13.025 --> 00:02:16.682
Let's say that I were to start
moving my hand up and down.

00:02:16.682 --> 00:02:18.429
So I move my hand up and down.

00:02:18.429 --> 00:02:19.729
What's going to happen?

00:02:19.729 --> 00:02:22.935
If I just did it once,

00:02:22.935 --> 00:02:25.380
what I'm gonna have is this lump of string

00:02:25.380 --> 00:02:28.752
move from the left to the right.

00:02:28.752 --> 00:02:31.414
So that's what it's
gonna look like at first.

00:02:31.414 --> 00:02:35.863
Then a few seconds later,
it's gonna look like this.

00:02:35.863 --> 00:02:37.834
It's gonna look something like this.

00:02:37.834 --> 00:02:39.927
You're gonna have this disturbance,

00:02:39.927 --> 00:02:43.604
which is this wave, this
lump that I just generated.

00:02:43.604 --> 00:02:48.277
It is going to move to the right.

00:02:48.277 --> 00:02:49.476
What's the medium?

00:02:49.476 --> 00:02:52.097
The medium in this case is the string.

00:02:52.097 --> 00:02:53.681
It is the string.

00:02:53.681 --> 00:02:55.368
What just happened there?

00:02:55.368 --> 00:02:58.151
When I jerk the string up,

00:02:58.151 --> 00:03:01.808
I'm disturbing those string
molecules right next to my hand.

00:03:01.808 --> 00:03:03.860
They're pulling on the
string molecules next to them

00:03:03.860 --> 00:03:05.465
pulling on the sting
molecules next to them.

00:03:05.465 --> 00:03:08.411
Then you have this traveling lump.

00:03:08.411 --> 00:03:10.910
Once again, these are
both examples of waves.

00:03:10.910 --> 00:03:15.339
Disturbances traveling through a medium.

00:03:15.339 --> 00:03:19.260
Now I can give other through a medium.

00:03:19.260 --> 00:03:20.642
I can give other examples.

00:03:20.642 --> 00:03:21.788
Sound waves.

00:03:21.788 --> 00:03:23.023
What causes sound waves?

00:03:23.023 --> 00:03:27.351
You have a bunch of air
particles all bouncing around

00:03:27.351 --> 00:03:32.329
at actually surprisingly fast speeds.

00:03:32.329 --> 00:03:33.609
But if you disturb them,

00:03:33.609 --> 00:03:36.108
if you cause something to, say, compress

00:03:36.108 --> 00:03:37.992
a bunch of air particles right here.

00:03:37.992 --> 00:03:40.532
These air particles get ultra-compressed.

00:03:40.532 --> 00:03:42.543
Some type of clap happens,

00:03:42.543 --> 00:03:44.656
so these get ultra-compressed.

00:03:44.656 --> 00:03:47.033
Then they're gonna bounce
on the ones next to them.

00:03:47.033 --> 00:03:49.430
Once again, you have this disturbance

00:03:49.430 --> 00:03:51.015
traveling through the medium.

00:03:51.015 --> 00:03:54.489
In this case, the medium is the air.

00:03:54.489 --> 00:03:56.786
The medium is the air.

00:03:56.786 --> 00:03:58.106
So, now that we've seen some

00:03:58.106 --> 00:04:00.320
classical notions of waves,

00:04:00.320 --> 00:04:03.368
let's think about something
a little bit more mysterious.

00:04:03.368 --> 00:04:07.086
That is the notion of light.

00:04:07.086 --> 00:04:12.086
Light definitely has wave like properties.

00:04:12.722 --> 00:04:15.224
Wave light can interfere with each other.

00:04:15.224 --> 00:04:17.682
We can do a whole other videos on light.

00:04:17.682 --> 00:04:22.682
If I were to take a barrier like that

00:04:24.012 --> 00:04:28.924
with two small slits in it.

00:04:28.924 --> 00:04:33.748
If I were to shine some light,

00:04:33.748 --> 00:04:35.710
one way to think about
it is these slits are

00:04:35.710 --> 00:04:40.464
the only place where the
disturbance gets through

00:04:40.464 --> 00:04:42.882
and then it would cause the light

00:04:42.882 --> 00:04:47.087
to propagate from each of them like that.

00:04:47.087 --> 00:04:50.013
Maybe I'm just drawing
the crests of the waves,

00:04:50.013 --> 00:04:52.289
but also come out from here.

00:04:52.289 --> 00:04:56.007
You can see where the two crests meet.

00:04:56.007 --> 00:05:00.497
They're going to constructively
enhance each other.

00:05:00.497 --> 00:05:03.138
They're going to constructively interfere.

00:05:03.138 --> 00:05:08.034
If you were to put some type
of a detector right over here,

00:05:08.034 --> 00:05:11.326
you would see the bright
points of the light

00:05:11.326 --> 00:05:14.089
and you would see the
dark points of the light.

00:05:14.089 --> 00:05:15.755
So light definitely behaves like a wave.

00:05:15.755 --> 00:05:17.380
I'm just showing you even one example of

00:05:17.380 --> 00:05:19.574
light behaving like a wave.

00:05:19.574 --> 00:05:22.805
But if it is a wave, that
means it needs to be or

00:05:22.805 --> 00:05:24.444
if we use our classical logic,

00:05:24.444 --> 00:05:25.086
you would say,

00:05:25.086 --> 00:05:26.127
well that means it's a disturbance

00:05:26.127 --> 00:05:28.168
traveling through a medium.

00:05:28.168 --> 00:05:30.423
But what is that medium?

00:05:30.423 --> 00:05:33.349
We have light coming from our sun.

00:05:33.349 --> 00:05:35.239
We call it sunlight.

00:05:35.239 --> 00:05:37.352
We have light coming,

00:05:37.352 --> 00:05:38.550
I keep wanting to make it a -

00:05:38.550 --> 00:05:40.338
actually our sun is white,

00:05:40.338 --> 00:05:42.471
we tend to draw it as a yellowish color,

00:05:42.471 --> 00:05:44.178
but that's just because of its -

00:05:44.178 --> 00:05:46.291
what happens is it goes
through the atmosphere.

00:05:46.291 --> 00:05:50.944
So you have the sun, you have the earth.

00:05:50.944 --> 00:05:52.711
This is not drawn to scale.

00:05:52.711 --> 00:05:54.743
Somehow that light is able to reach us

00:05:54.743 --> 00:05:59.743
over 93 million miles.

00:06:00.107 --> 00:06:02.240
What's it going through?

00:06:02.240 --> 00:06:05.694
Is it a disturbance
traveling through a medium?

00:06:05.694 --> 00:06:07.461
Well, for a long time, people said,

00:06:07.461 --> 00:06:08.579
well it must be.

00:06:08.579 --> 00:06:10.773
It has these wave-like properties.

00:06:10.773 --> 00:06:14.471
It seems to be traveling with a velocity,

00:06:14.471 --> 00:06:16.055
the speed of light.

00:06:16.055 --> 00:06:18.920
So there must be medium that
it is traveling through.

00:06:18.920 --> 00:06:20.972
People theorize what this medium is.

00:06:20.972 --> 00:06:23.491
They called it the luminiferous ether.

00:06:23.491 --> 00:06:25.584
Let me write that down
cause it's a fun word.

00:06:25.584 --> 00:06:27.636
It's a good name for a band.

00:06:27.636 --> 00:06:32.636
Luminiferous. Lumine, no
I'm not spelling it right.

00:06:34.045 --> 00:06:39.045
Luminiferous ether.

00:06:39.595 --> 00:06:44.595
It was this idea that maybe,
even in the vacuum of space,

00:06:45.910 --> 00:06:50.367
you have this substance.

00:06:50.367 --> 00:06:54.850
This luminiferous ether that
the light is traveling through.

00:06:54.850 --> 00:06:57.706
That it's somehow a disturbance

00:06:57.706 --> 00:07:02.082
in that luminiferous ether.

00:07:02.082 --> 00:07:04.337
Now, what we're gonna do in future videos,

00:07:04.337 --> 00:07:05.454
is we're gonna test that.

00:07:05.454 --> 00:07:06.633
We're gonna see if
that's actually the case

00:07:06.633 --> 00:07:08.563
because what's interesting
about if there is

00:07:08.563 --> 00:07:10.696
a luminiferous ether,

00:07:10.696 --> 00:07:12.972
we're not gonna be stationary relative to

00:07:12.972 --> 00:07:14.394
that luminiferous ether.

00:07:14.394 --> 00:07:17.604
In fact, we're orbiting around the sun.

00:07:17.604 --> 00:07:21.038
The sun is orbiting around
the center of the galaxy.

00:07:21.038 --> 00:07:23.292
There's no way that we're gonna be

00:07:23.292 --> 00:07:27.011
stationary relative to
that luminiferous ether.

00:07:27.011 --> 00:07:29.083
If we're not stationary relative to that

00:07:29.083 --> 00:07:31.074
luminiferous ether, we should be able to

00:07:31.074 --> 00:07:33.065
detect how light behaves.

00:07:33.065 --> 00:07:36.072
If it's going in the direction of ether

00:07:36.072 --> 00:07:38.449
or if it's going against the direction of

00:07:38.449 --> 00:07:41.558
the relative movement of
the ether relative to us.

00:07:41.558 --> 00:07:43.183
So anyway, I'll leave you there.

00:07:43.183 --> 00:07:44.829
This mystery of science.

00:07:44.829 --> 00:07:47.104
Waves, disturbance through a medium.

00:07:47.104 --> 00:07:48.303
We saw that with the water,

00:07:48.303 --> 00:07:49.806
with the air, with the string.

00:07:49.806 --> 00:07:51.554
But what about light?

00:07:51.554 --> 00:07:54.093
Is there a luminiferous ether?

00:07:54.093 --> 00:07:56.477
Put a question mark there.


Cell signaling in yeast reproduction

WEBVTT
Kind: captions
Language: en

00:00:00.258 --> 00:00:02.338
- All of the examples
of cell-cell signaling

00:00:02.338 --> 00:00:04.478
that we've looked at
so far have been cells

00:00:04.478 --> 00:00:06.118
within an organism, but what I want

00:00:06.118 --> 00:00:08.238
to do in this video is
point out that you can

00:00:08.238 --> 00:00:11.078
also have cell-cell signaling

00:00:11.078 --> 00:00:12.638
between different organisms,

00:00:12.638 --> 00:00:15.818
and even between different
unicellular organisms.

00:00:15.818 --> 00:00:18.118
And so what we have
here, these are pictures

00:00:18.118 --> 00:00:19.478
of yeast cells.

00:00:19.478 --> 00:00:22.548
Yeast are unicellular eukaryotic

00:00:22.548 --> 00:00:25.218
organisms which means they have

00:00:25.218 --> 00:00:28.848
a nucleus and they are officially fungi,

00:00:28.848 --> 00:00:31.118
and what you see happening in this picture

00:00:31.118 --> 00:00:33.338
right over here, it looks like you have

00:00:33.338 --> 00:00:36.648
a second yeast cell budding
off of the first one.

00:00:36.648 --> 00:00:38.968
This happens fundamentally
through mitosis,

00:00:38.968 --> 00:00:41.658
but yeast can actually
reproduce in two different ways.

00:00:41.658 --> 00:00:44.598
It can reproduce asexually
through mitosis like this,

00:00:44.598 --> 00:00:47.098
but it can also reproduce
sexually, and that's

00:00:47.098 --> 00:00:48.818
where we're going to talk a little bit

00:00:48.818 --> 00:00:51.458
about signaling between
the cells, and they do

00:00:51.458 --> 00:00:53.198
this with mating factors, and this is just

00:00:53.198 --> 00:00:55.298
an interesting discussion
of yeast generally.

00:00:55.298 --> 00:00:58.238
So if you start with a yeast cell,

00:00:58.238 --> 00:01:00.588
so this is a yeast cell right over here,

00:01:00.588 --> 00:01:03.438
and this is a diploid yeast cell,

00:01:03.438 --> 00:01:06.348
so it has its full complement

00:01:06.348 --> 00:01:07.908
of chromosomes.

00:01:07.908 --> 00:01:11.838
So it's going to have 16 pairs,

00:01:11.838 --> 00:01:14.008
16 pairs of chromosomes,

00:01:14.008 --> 00:01:16.928
or 32 total chromosomes.

00:01:16.928 --> 00:01:18.469
That's a diploid.

00:01:18.469 --> 00:01:20.728
So through mitosis it could split apart

00:01:20.728 --> 00:01:22.298
and it would do so like this.

00:01:22.298 --> 00:01:26.078
The one that buds off for most species

00:01:26.078 --> 00:01:28.098
of yeast will be smaller,
although they're some

00:01:28.098 --> 00:01:30.608
that kind of do more even mitosis.

00:01:30.608 --> 00:01:34.858
But through mitosis you could produce

00:01:34.858 --> 00:01:38.558
two diploid yeast cells

00:01:38.558 --> 00:01:39.558
just like this.

00:01:39.558 --> 00:01:42.318
So all of these characters right over

00:01:42.318 --> 00:01:44.838
here are a diploid.

00:01:44.838 --> 00:01:47.188
And actually, just to stress,

00:01:47.188 --> 00:01:48.688
that they are eukaryotes.

00:01:48.688 --> 00:01:51.228
Let me draw a little nuclear membrane

00:01:51.228 --> 00:01:52.418
in here.

00:01:52.418 --> 00:01:54.638
But it can also divide

00:01:54.638 --> 00:01:56.568
through meiosis,

00:01:56.568 --> 00:01:59.118
so this is mitosis right over here,

00:01:59.118 --> 00:02:01.868
mitosis right over here help produce

00:02:01.868 --> 00:02:03.478
these two, but you can also go through

00:02:03.478 --> 00:02:05.558
meiosis.

00:02:05.558 --> 00:02:07.448
Meiosis,

00:02:07.448 --> 00:02:09.488
and if we go through meiosis we're going

00:02:09.488 --> 00:02:12.458
to produce four cells
and what's interesting

00:02:12.458 --> 00:02:15.198
about these is that these will come in one

00:02:15.198 --> 00:02:17.688
of two varieties, and you could view these

00:02:17.688 --> 00:02:20.878
as the sex of these yeast cells.

00:02:20.878 --> 00:02:22.368
So they could either be

00:02:22.368 --> 00:02:25.328
in the type a variety,

00:02:25.328 --> 00:02:28.358
so let's make these two type a.

00:02:28.358 --> 00:02:31.948
So that's a type a, that's
a type a right there,

00:02:31.948 --> 00:02:35.648
or they could be in
the type alpha variety.

00:02:35.648 --> 00:02:38.398
So this is a , I'm using

00:02:38.398 --> 00:02:40.438
a different color.

00:02:40.438 --> 00:02:41.898
So this is

00:02:41.898 --> 00:02:45.018
a type alpha,

00:02:45.018 --> 00:02:46.618
and this is another type alpha,

00:02:46.618 --> 00:02:47.838
and all four of these are going

00:02:47.838 --> 00:02:50.058
to come through meiosis

00:02:50.058 --> 00:02:52.738
from this original diploid cell.

00:02:52.738 --> 00:02:54.078
And since we went through meiosis,

00:02:54.078 --> 00:02:56.528
each of these are going to be haploid.

00:02:56.528 --> 00:02:58.238
So these are all going to be haploids.

00:02:58.238 --> 00:03:01.698
This is going to be 16 chromosomes total,

00:03:01.698 --> 00:03:05.358
16 chromosomes, chromosomes,

00:03:05.358 --> 00:03:06.568
each of them.

00:03:06.568 --> 00:03:07.748
So they're all going

00:03:07.748 --> 00:03:10.598
to be haploid

00:03:10.598 --> 00:03:12.448
and in fact, each of these can,

00:03:12.448 --> 00:03:14.538
to some degree, live a life of their own

00:03:14.538 --> 00:03:17.078
and continue to reproduce through mitosis.

00:03:17.078 --> 00:03:18.498
That's worth pointing out,

00:03:18.498 --> 00:03:19.818
that's interesting.

00:03:19.818 --> 00:03:21.498
You normally wouldn't associate sex cells,

00:03:21.498 --> 00:03:24.278
if it was anything but
humans you wouldn't think

00:03:24.278 --> 00:03:25.818
that sperm cells would
be able to replicate

00:03:25.818 --> 00:03:27.408
on their own, or egg cells would be able

00:03:27.408 --> 00:03:28.918
to replicate on their own but in the case

00:03:28.918 --> 00:03:30.278
of yeast, they actually can.

00:03:30.278 --> 00:03:33.118
So this type a cell could turn into,

00:03:33.118 --> 00:03:34.838
through mitosis, it could turn into

00:03:34.838 --> 00:03:37.608
two type a cells.

00:03:37.608 --> 00:03:41.298
So this is all just interesting
background, mitosis.

00:03:41.298 --> 00:03:42.768
So even the products of meiosis can

00:03:42.768 --> 00:03:44.538
then mitose themselves.

00:03:44.538 --> 00:03:46.788
That's all interesting,
this is all the set up

00:03:46.788 --> 00:03:49.318
to think about how they actually signal

00:03:49.318 --> 00:03:51.848
because these, these haploid cells

00:03:51.848 --> 00:03:53.918
that are producers of
byproduct of meiosis,

00:03:53.918 --> 00:03:55.298
these are, these right over here,

00:03:55.298 --> 00:03:57.508
they all came from the original ancestor,

00:03:57.508 --> 00:03:59.528
which is actually fairly
typical when we're talking

00:03:59.528 --> 00:04:01.968
about reproducing and
kind of pseudo-sexually

00:04:01.968 --> 00:04:03.908
reproducing yeast cells.

00:04:03.908 --> 00:04:06.698
They don't have to, maybe
one of the type alphas

00:04:06.698 --> 00:04:09.818
came from another ancestor,
but what happens is

00:04:09.818 --> 00:04:12.378
they each release what's
called mating factors,

00:04:12.378 --> 00:04:14.788
or you can consider them
to be mating pheromones.

00:04:14.788 --> 00:04:17.138
So this type a right over here, it's going

00:04:17.138 --> 00:04:20.028
to produce, it's going to produce

00:04:20.028 --> 00:04:22.448
the type a mating factors and it's going

00:04:22.448 --> 00:04:25.198
to release them into the space around it.

00:04:25.198 --> 00:04:28.368
So it's releasing those type a

00:04:28.368 --> 00:04:29.848
mating factors and then

00:04:29.848 --> 00:04:31.538
the alphas are going to
release the type alpha

00:04:31.538 --> 00:04:33.108
mating factors.

00:04:33.108 --> 00:04:35.928
So I'll do that in this
orange-ish brown color.

00:04:35.928 --> 00:04:38.578
So they're going to release the type alpha

00:04:38.578 --> 00:04:39.818
mating factors.

00:04:39.818 --> 00:04:42.448
And what happens is
each type has receptors

00:04:42.448 --> 00:04:45.568
for the other type's factors.

00:04:45.568 --> 00:04:48.978
So the type a is going

00:04:48.978 --> 00:04:50.568
to have receptors

00:04:50.568 --> 00:04:52.658
for the type alpha,

00:04:52.658 --> 00:04:54.098
for the type alpha.

00:04:54.098 --> 00:04:56.728
It's going to be in all over the outside

00:04:56.728 --> 00:04:58.118
of the cell, and the type alpha's going

00:04:58.118 --> 00:05:00.688
to have type receptors for the type a.

00:05:00.688 --> 00:05:03.198
Receptors, I'm going to do that in orange.

00:05:03.198 --> 00:05:05.928
It's going to have
receptors for the type a.

00:05:05.928 --> 00:05:07.958
Let me just draw it like
that, that's not exactly

00:05:07.958 --> 00:05:09.538
what they look like, or
actually nowhere close

00:05:09.538 --> 00:05:11.378
to what they look like
but it gives you a sense

00:05:11.378 --> 00:05:12.828
of things.

00:05:12.828 --> 00:05:14.888
It gives you a sense of things.

00:05:14.888 --> 00:05:17.738
And as through these
receptors it starts bonding

00:05:17.738 --> 00:05:20.588
a lot of, say we're on the
alpha cell right over here,

00:05:20.588 --> 00:05:23.708
it starts bonding to a lot
of these mating pheromones,

00:05:23.708 --> 00:05:25.578
these mating factors.

00:05:25.578 --> 00:05:28.168
Then the yeast cell
itself, it doesn't move

00:05:28.168 --> 00:05:30.308
but it starts growing in that direction,

00:05:30.308 --> 00:05:31.898
it starts growing in the direction where

00:05:31.898 --> 00:05:34.668
it says, "Hey, I'm sensing a
lot of this mating factor."

00:05:34.668 --> 00:05:37.118
So it starts growing in this direction,

00:05:37.118 --> 00:05:38.998
it starts doing something like that.

00:05:38.998 --> 00:05:40.268
And the corresponding thing is going

00:05:40.268 --> 00:05:42.348
to happen for the type a cell.

00:05:42.348 --> 00:05:45.578
It's going to have the
alpha factors attached

00:05:45.578 --> 00:05:48.068
onto it, and because
of that it says, "Okay,

00:05:48.068 --> 00:05:51.088
"I'm sensing once again, the factors."

00:05:51.088 --> 00:05:53.318
The ligand, it attaches to the receptor,

00:05:53.318 --> 00:05:54.438
that's the sensing part.

00:05:54.438 --> 00:05:57.418
Then you have signal
transduction and it's actually,

00:05:57.418 --> 00:05:59.198
it's not too dissimilar

00:05:59.198 --> 00:06:01.058
from the MAPK,

00:06:01.058 --> 00:06:04.788
the MAPK transduction pathway

00:06:04.788 --> 00:06:06.658
that we talk about in other videos.

00:06:06.658 --> 00:06:08.178
And then the response the cell has is,

00:06:08.178 --> 00:06:11.128
once again, to start
growing in the direction

00:06:11.128 --> 00:06:13.648
of where it seems that
these mating factors

00:06:13.648 --> 00:06:14.988
are coming from.

00:06:14.988 --> 00:06:17.858
And these kind of
elongation, these outgrowths

00:06:17.858 --> 00:06:20.578
of these haploid yeast
cells, they're actually

00:06:20.578 --> 00:06:22.818
called shmoos.

00:06:22.818 --> 00:06:25.258
So that right there, that is a shmoo.

00:06:25.258 --> 00:06:27.738
And you might say, where
did that come from?

00:06:27.738 --> 00:06:30.248
Well, it came from this
character right over here,

00:06:30.248 --> 00:06:33.058
which was a cartoon
character in the middle

00:06:33.058 --> 00:06:35.918
20th century, and I'll, you know...

00:06:39.648 --> 00:06:41.968
well, let's avoid any
snickering over the course

00:06:41.968 --> 00:06:44.048
of this video, but that's
what it looks like.

00:06:44.048 --> 00:06:46.028
And as they grow to each other,

00:06:46.028 --> 00:06:49.138
that actually allows them to join together

00:06:49.138 --> 00:06:51.488
and form another diploid,

00:06:51.488 --> 00:06:53.478
another diploid yeast cell.

00:06:53.478 --> 00:06:56.358
So if this process were to continue,

00:06:56.358 --> 00:06:58.268
if this process were to continue,

00:06:58.268 --> 00:07:01.378
these two shmoos will join together

00:07:01.378 --> 00:07:05.318
and the genetic makeup joins together

00:07:05.318 --> 00:07:07.948
and so we could get another diploid cell.

00:07:07.948 --> 00:07:10.588
And now this diploid cell is going to have

00:07:10.588 --> 00:07:14.178
kind of a new combination

00:07:14.178 --> 00:07:16.648
of DNA, so it could benefit from some

00:07:16.648 --> 00:07:17.818
of the variation

00:07:17.818 --> 00:07:20.738
of sexual reproduction.

00:07:20.738 --> 00:07:21.838
This is diploid.

00:07:21.838 --> 00:07:23.238
Although for yeast cells,

00:07:23.238 --> 00:07:26.218
they've like studied it
because it's not clear

00:07:26.218 --> 00:07:27.518
that these are necessarily coming from

00:07:27.518 --> 00:07:29.138
a separate gene pool.

00:07:29.138 --> 00:07:30.648
These actually could have the same

00:07:30.648 --> 00:07:32.298
ancestor molecule so it is a bit

00:07:32.298 --> 00:07:34.058
of an open question in biology

00:07:34.058 --> 00:07:36.228
of why do they have this type of sexual

00:07:36.228 --> 00:07:38.018
reproduction, especially when they're

00:07:38.018 --> 00:07:40.318
coming from when these are essentially

00:07:40.318 --> 00:07:42.818
sibling cells as a byproduct of meiosis.

00:07:42.818 --> 00:07:44.498
But anyway, the whole point of this

00:07:44.498 --> 00:07:48.298
is one, to appreciate
these fascinating things

00:07:48.298 --> 00:07:49.738
that are happening even at the level

00:07:49.738 --> 00:07:52.218
of yeast cells, and that you do have

00:07:52.218 --> 00:07:53.918
cell-cell signaling, not just within

00:07:53.918 --> 00:07:56.498
an organism, but across organisms,

00:07:56.498 --> 00:08:00.018
especially, or even unicellular organisms.


Example of signal transduction pathway

WEBVTT
Kind: captions
Language: en

00:00:00.484 --> 00:00:02.351
- [Voiceover] In previous
videos on cell signaling,

00:00:02.351 --> 00:00:04.928
we talk about the idea
that if we have a cell

00:00:04.928 --> 00:00:08.807
right over there and let's say
it has some type of receptor.

00:00:08.807 --> 00:00:11.325
It doesn't actually have to
be on the cellular membrane,

00:00:11.325 --> 00:00:12.712
but I'll put it there for now.

00:00:15.223 --> 00:00:18.523
It can bind to some ligand,
that when the ligand

00:00:18.523 --> 00:00:22.365
binds to the receptor and
it's usually particular,

00:00:22.365 --> 00:00:23.715
the ligand is usually particular

00:00:23.715 --> 00:00:25.339
to the receptor and vice versa,

00:00:25.339 --> 00:00:28.984
it can set off a whole cascade of events.

00:00:28.984 --> 00:00:32.289
In particular, once it binds,
so let me actually draw

00:00:32.289 --> 00:00:35.288
the ligand bound to the receptor,

00:00:35.288 --> 00:00:38.376
you can have a signal that
tells the cell to do something.

00:00:38.376 --> 00:00:41.186
It might activate some
genes, it might change

00:00:41.186 --> 00:00:43.650
the metabolism of the cell in some way.

00:00:43.650 --> 00:00:46.387
And this signal that goes from
the receptor into the cell

00:00:46.387 --> 00:00:48.326
to make the cell behave in some way,

00:00:48.326 --> 00:00:50.965
we call that signal transduction.

00:00:50.965 --> 00:00:55.791
We call it transduction,
signal transduction.

00:00:55.791 --> 00:00:57.092
In the previous video, I was kind of

00:00:57.092 --> 00:00:58.624
hand wavy about it, and
you might have been saying,

00:00:58.624 --> 00:01:02.653
"Well how does a signal
actually go into the cell?

00:01:02.653 --> 00:01:04.360
"How does it actually
move through the cell

00:01:04.360 --> 00:01:06.610
"and how does it actually
make things happen?"

00:01:06.610 --> 00:01:08.362
And what I wanna do in
this video is I'm not gonna

00:01:08.362 --> 00:01:09.956
go into all of the details,
but I'm gonna give you

00:01:09.956 --> 00:01:14.514
an appreciation for how
transduction can actually occur.

00:01:14.514 --> 00:01:16.653
Hopefully it'll also give you appreciation

00:01:16.653 --> 00:01:19.093
for how complex biological systems,

00:01:19.093 --> 00:01:20.857
including you and me, and even each of our

00:01:20.857 --> 00:01:23.388
individual cells actually are.

00:01:23.388 --> 00:01:26.651
So this pathway that we're seeing up here,

00:01:26.651 --> 00:01:28.392
and you can see that
there's a bunch of pathways

00:01:28.392 --> 00:01:30.958
that all kind of work together and overlap

00:01:30.958 --> 00:01:33.926
in terms of the enzymes and
the proteins that are involved.

00:01:33.926 --> 00:01:35.486
This, as the diagram calls,

00:01:35.486 --> 00:01:38.941
is the Classical Map kinase pathway.

00:01:38.941 --> 00:01:41.093
If you're wondering, "What
does Map kinase stand for?"

00:01:41.093 --> 00:01:44.616
And oftentimes people will
just say MAPK or M-A-P-K,

00:01:44.616 --> 00:01:47.525
it stands for mitogen, M for mitogen,

00:01:47.525 --> 00:01:50.788
mitogen-activated protein kinases.

00:01:50.788 --> 00:01:55.732
And you might be saying,
"What does mitogen mean?"

00:01:55.732 --> 00:01:59.820
Well, mitogen refers to
things that cause cells

00:01:59.820 --> 00:02:03.652
to mitose, to actually

00:02:03.652 --> 00:02:08.168
go into mitosis, to start
replicating themselves.

00:02:08.168 --> 00:02:10.963
Now, what is mitogen-activated?

00:02:10.963 --> 00:02:14.727
So this pathway is going to
be activated by a mitogen.

00:02:14.727 --> 00:02:18.755
Mitogen-acivated protein kinase.

00:02:18.755 --> 00:02:19.928
Well, a protein kinase,

00:02:19.928 --> 00:02:23.124
a kinase, and we've seen
kinases multiple times.

00:02:23.124 --> 00:02:26.444
They're involved in many, many,
many biological mechanisms.

00:02:26.444 --> 00:02:28.590
These are general term for enzymes

00:02:28.590 --> 00:02:31.331
that help take a higher energy phosphate,

00:02:31.331 --> 00:02:33.224
or especially, I should
say, a higher energy bond

00:02:33.224 --> 00:02:35.552
or a phosphate, part of an ATP

00:02:35.552 --> 00:02:38.782
or a GTP and transfers them
to different molecules,

00:02:38.782 --> 00:02:40.574
and as they transfer them
to different molecules,

00:02:40.574 --> 00:02:42.342
it's able to leverage that energy

00:02:42.342 --> 00:02:45.505
to actually facilitate
some type of a mechanism.

00:02:45.505 --> 00:02:48.137
Now, as I said, I'm not gonna
go into all the details here.

00:02:48.137 --> 00:02:49.546
This is actually quite complex,

00:02:49.546 --> 00:02:51.125
but I want to make a
little bit sense of it.

00:02:51.125 --> 00:02:53.377
And we're actually gonna talk about

00:02:53.377 --> 00:02:56.790
a few proteins and a few
enzymes that are actually

00:02:56.790 --> 00:03:00.250
fairly important to modern
biological research.

00:03:00.250 --> 00:03:02.259
So what you have right over here,

00:03:02.259 --> 00:03:05.660
I'll start with this
molecule right over here.

00:03:05.660 --> 00:03:07.339
This is the ligand.

00:03:07.339 --> 00:03:09.619
This is the ligand, it's
going to be released

00:03:09.619 --> 00:03:12.760
by some other part of
the biological system,

00:03:12.760 --> 00:03:15.203
from some other cell.

00:03:15.203 --> 00:03:20.154
And this EGF, this stands
for epidermal growth factor.

00:03:20.154 --> 00:03:23.551
The 1986 Nobel Prize in
medicine was actually given

00:03:23.551 --> 00:03:27.255
for the discovery of EGF,
of epidermal growth factor.

00:03:27.255 --> 00:03:28.822
Now this is going to be the ligand,

00:03:28.822 --> 00:03:31.910
and this is essentially when this attaches

00:03:31.910 --> 00:03:34.428
or when this binds to a receptor,

00:03:34.428 --> 00:03:37.495
that's going to cause a
signal to be transduced.

00:03:37.495 --> 00:03:40.084
You're gonna have the
transduction going into the cell.

00:03:40.084 --> 00:03:41.888
And so you can imagine, it's going to bind

00:03:41.888 --> 00:03:44.466
to this membrane receptor,

00:03:44.466 --> 00:03:47.286
and so EGFR literally stands for

00:03:47.286 --> 00:03:51.837
epidermal growth factor
receptor, EGF receptor.

00:03:51.837 --> 00:03:55.158
And it's part of this protein
complex and once this binds,

00:03:55.158 --> 00:03:59.432
it's able to help activate

00:03:59.432 --> 00:04:01.384
RAS right over here.

00:04:01.384 --> 00:04:03.693
RAS, once again, all of these names,

00:04:03.693 --> 00:04:06.063
they have these interesting
histories associated with them.

00:04:06.063 --> 00:04:08.239
This stands for rat sarcoma,

00:04:10.080 --> 00:04:14.155
and sarcomas are cancers

00:04:14.155 --> 00:04:16.813
in certain tissues in the body.

00:04:16.813 --> 00:04:19.889
It was first discovered
associated with certain cancers,

00:04:19.889 --> 00:04:23.952
that rats that had certain sarcomas,

00:04:23.952 --> 00:04:26.392
that they were able to see
that there were mutations

00:04:26.392 --> 00:04:30.187
in the genes that
produced the RAS protein.

00:04:30.187 --> 00:04:33.426
Because of those
mutations, the RAS protein

00:04:33.426 --> 00:04:35.914
that the enzymes associated with it

00:04:35.914 --> 00:04:37.861
were in their activated mode.

00:04:37.861 --> 00:04:39.394
And because they were
in the activated mode,

00:04:39.394 --> 00:04:42.146
this mechanism was kind of overactive.

00:04:42.146 --> 00:04:46.650
And any of the stop signals
weren't actually happening.

00:04:46.650 --> 00:04:49.181
And so you could imagine a
mechanism right over here

00:04:49.181 --> 00:04:51.259
that is about cell differentiation,

00:04:51.259 --> 00:04:54.150
that if this mechanism
proceeds, it's eventually

00:04:54.150 --> 00:04:57.622
going to tell the DNA,
some portions of the DNA,

00:04:57.622 --> 00:04:59.355
especially the portions of the DNA

00:04:59.355 --> 00:05:02.118
that are involved with DNA replication,

00:05:02.118 --> 00:05:04.292
with cell division, with mitosis,

00:05:04.292 --> 00:05:05.192
those are gonna go crazy,

00:05:05.192 --> 00:05:07.584
and that's exactly what happens in cancer.

00:05:07.584 --> 00:05:08.988
So this pathway is actually

00:05:08.988 --> 00:05:11.217
a very important pathway in cancer.

00:05:11.217 --> 00:05:14.173
You see right over here, you
actually see the Map kinase,

00:05:14.173 --> 00:05:17.240
it's often called, or was
originally called ERK,

00:05:18.162 --> 00:05:21.353
which is extracellular
signal regulated kinase.

00:05:21.353 --> 00:05:24.082
But this in an incredibly
important pathway

00:05:24.082 --> 00:05:27.857
to cancer researchers, and
they actively are looking for

00:05:27.857 --> 00:05:30.374
different types of drugs,
different types of molecules

00:05:30.374 --> 00:05:33.604
that can down regulate
this type of pathway.

00:05:33.604 --> 00:05:35.227
So the whole point of
this video, once again,

00:05:35.227 --> 00:05:37.119
I'm not going into all of the details

00:05:37.119 --> 00:05:39.559
on the Map kinase pathway,

00:05:39.559 --> 00:05:40.989
was to give you an appreciation

00:05:40.989 --> 00:05:42.788
for how complex transduction is.

00:05:42.788 --> 00:05:46.446
You have this cascade of
this signal which is really

00:05:46.446 --> 00:05:48.763
these phosphate groups
originally transferred

00:05:48.763 --> 00:05:53.763
from a GTP going to Ras,
and it keeps cascading down

00:05:53.784 --> 00:05:57.950
all the way until you actually
have the DNA being told to,

00:05:57.950 --> 00:06:02.659
or you start activating mechanisms

00:06:02.659 --> 00:06:06.185
where the DNA is going
to start replicating,

00:06:06.185 --> 00:06:07.789
and then the cell itself

00:06:07.789 --> 00:06:09.920
is going to proliferate and differentiate.

00:06:11.330 --> 00:06:14.518
This needs to happen in practically
every cells in our body,

00:06:14.518 --> 00:06:18.419
but there's all sorts of kind of factors

00:06:18.419 --> 00:06:19.719
that keep it from going crazy.

00:06:19.719 --> 00:06:21.941
But if you have a
mutation in something like

00:06:21.941 --> 00:06:25.082
the Ras gene which codes
for the Ras protein,

00:06:25.082 --> 00:06:28.143
then you could end up with
an actual cancer cell.

00:06:28.143 --> 00:06:30.138
So hopefully this give you a
little bit more appreciation

00:06:30.138 --> 00:06:32.773
for how transduction actually occurs.


Introduction to nouns and verbs

WEBVTT
Kind: captions
Language: en

00:00:00.137 --> 00:00:01.397
- [Voiceover] Let's
start becoming familiar

00:00:01.397 --> 00:00:02.941
with our parts of speech.

00:00:02.941 --> 00:00:05.602
And we're gonna start with
the two most fundamental ones.

00:00:05.602 --> 00:00:09.483
First, the noun, which you
will often see described

00:00:09.483 --> 00:00:14.483
as a person, a place or a thing.

00:00:16.452 --> 00:00:19.296
And we're also gonna talk about verbs.

00:00:19.296 --> 00:00:24.296
A verb is something that
is some type of action.

00:00:24.314 --> 00:00:26.021
And at first this might seem a little bit

00:00:26.021 --> 00:00:28.560
hard to understand,
what is this word noun,

00:00:28.560 --> 00:00:30.023
this word verb?

00:00:30.023 --> 00:00:31.710
But as we take, do a bunch of examples,

00:00:31.710 --> 00:00:34.038
this will hopefully it'll
make a little bit more sense.

00:00:34.038 --> 00:00:36.375
So let's first look at
this first sentence.

00:00:36.375 --> 00:00:38.020
Bill likes dessert.

00:00:38.020 --> 00:00:39.483
So I encourage you to pause the video,

00:00:39.483 --> 00:00:40.600
look at each of these words

00:00:40.600 --> 00:00:42.369
and say is that a person, place or thing?

00:00:42.369 --> 00:00:43.769
Or is it some type of action?

00:00:43.769 --> 00:00:44.602
Or is it neither?

00:00:44.602 --> 00:00:47.407
And so it wouldn't be a noun or a verb.

00:00:47.407 --> 00:00:48.361
Let's do it together.

00:00:48.361 --> 00:00:51.211
So in Bill likes dessert,
Bill is a person.

00:00:51.211 --> 00:00:52.918
So it is a person, place or thing.

00:00:52.918 --> 00:00:56.148
So this, the word Bill is a noun.

00:00:56.148 --> 00:00:59.419
So that right over there,
Bill, that is a noun.

00:00:59.419 --> 00:01:02.325
And then Bill likes dessert.

00:01:02.325 --> 00:01:04.864
So likes is not a person, place or thing.

00:01:04.864 --> 00:01:06.551
That would not be a noun.

00:01:06.551 --> 00:01:08.440
But dessert is a person, place or thing.

00:01:08.440 --> 00:01:10.208
In this case it is a thing.

00:01:10.208 --> 00:01:13.397
So dessert is also gonna be a noun.

00:01:13.397 --> 00:01:17.156
So we have two nouns, we have
two nouns in this sentence.

00:01:17.156 --> 00:01:18.659
Bill and dessert.

00:01:18.659 --> 00:01:20.021
But what is likes?

00:01:20.021 --> 00:01:22.073
What's the action that Bill is taking?

00:01:22.073 --> 00:01:27.050
Bill likes dessert, so
likes is going to be a verb.

00:01:27.050 --> 00:01:28.960
Or likes is a verb.

00:01:28.960 --> 00:01:32.643
So that is a verb.

00:01:32.643 --> 00:01:33.951
Let's do another example.

00:01:33.951 --> 00:01:35.543
I slept.

00:01:35.543 --> 00:01:38.482
Once again pause the video,
see if you can figure out

00:01:38.482 --> 00:01:41.618
the noun and the verb.

00:01:41.618 --> 00:01:45.559
Alright so we start with I,
is I a person, place or thing?

00:01:45.559 --> 00:01:48.078
Yeah its a person, its whoever
is saying the sentence.

00:01:48.078 --> 00:01:49.832
In this case, I guess its me.

00:01:49.832 --> 00:01:52.479
So this would be a noun.

00:01:52.479 --> 00:01:55.832
So let me do that in our noun color

00:01:55.832 --> 00:01:57.457
which is going to be yellow.

00:01:57.457 --> 00:02:00.911
So this is a noun, I.

00:02:00.911 --> 00:02:03.268
And then slept is not a
person, place or thing

00:02:03.268 --> 00:02:06.843
its an action, its what I did, I slept.

00:02:06.843 --> 00:02:11.843
So slept is a verb.

00:02:12.979 --> 00:02:15.478
So we had one noun, one verb.

00:02:15.478 --> 00:02:16.376
Let's look at this next sentence.

00:02:16.376 --> 00:02:18.591
The pretty pig took a bath.

00:02:18.591 --> 00:02:20.298
Once again, pause the
video and see if you can

00:02:20.298 --> 00:02:22.614
identify the persons, places
or things or the nouns

00:02:22.614 --> 00:02:25.499
and see if you can identify any verbs.

00:02:25.499 --> 00:02:28.587
So the pretty pig, and we're
gonna cover what the is

00:02:28.587 --> 00:02:31.289
but the by itself is not
a person, place or thing,

00:02:31.289 --> 00:02:32.854
i just did, to kind of get a little ahead,

00:02:32.854 --> 00:02:33.870
its called an article

00:02:33.870 --> 00:02:35.746
and we'll talk more
about that in the future.

00:02:35.746 --> 00:02:37.953
Pretty by itself is not
a person, place or thing

00:02:37.953 --> 00:02:41.001
and its also not an action,
so let's ignore that for now

00:02:41.001 --> 00:02:42.707
and we'll get back to that.

00:02:42.707 --> 00:02:45.897
But pig, that is a person, place or thing.

00:02:45.897 --> 00:02:50.468
So pig is a noun, pig is a noun.

00:02:50.468 --> 00:02:53.028
And then took, not a
person, place or thing.

00:02:53.028 --> 00:02:54.776
A, not a person, place or thing.

00:02:54.776 --> 00:02:57.661
Bath, well a bath, a bath is a thing.

00:02:57.661 --> 00:02:59.347
So that is also a noun.

00:02:59.347 --> 00:03:01.887
So those are the nouns right over there.

00:03:01.887 --> 00:03:05.747
So pig, pig and bath.

00:03:05.747 --> 00:03:07.453
Now what's our verb?

00:03:07.453 --> 00:03:09.140
There's one verb in this sentence.

00:03:09.140 --> 00:03:10.949
And its what the pig did,
the action the pig did,

00:03:10.949 --> 00:03:15.072
the pig took, took
something, it took a bath.

00:03:15.072 --> 00:03:16.942
So that's our action right over there,

00:03:16.942 --> 00:03:18.181
that's our verb.

00:03:18.181 --> 00:03:21.513
Took is our, is our verb.

00:03:21.513 --> 00:03:22.711
I think we're getting the hang of this,

00:03:22.711 --> 00:03:23.727
lets keep going.

00:03:23.727 --> 00:03:27.080
The funny bird ran quickly.

00:03:27.080 --> 00:03:30.676
Once again, pause the video,
see if you can work it out.

00:03:30.676 --> 00:03:33.114
Well the by itself is not
a person, place or thing.

00:03:33.114 --> 00:03:34.881
Funny by itself it not
a person, place or thing

00:03:34.881 --> 00:03:37.197
and neither of these are actions.

00:03:37.197 --> 00:03:38.762
Bird is a person, place or thing,

00:03:38.762 --> 00:03:39.859
its a thing.

00:03:39.859 --> 00:03:44.207
So bird, bird is a noun.

00:03:44.207 --> 00:03:46.096
Bird is a noun.

00:03:46.096 --> 00:03:47.559
Ran, that's what the bird did,

00:03:47.559 --> 00:03:50.708
that's the action, so
that's gonna be a verb.

00:03:50.708 --> 00:03:54.833
And quickly is neither an action nor is it

00:03:54.833 --> 00:03:57.372
a person, place or thing
and we'll study this part

00:03:57.372 --> 00:03:59.648
of speech in the future.

00:03:59.648 --> 00:04:00.704
Let's look at the next sentence.

00:04:00.704 --> 00:04:02.533
He ate the watch.

00:04:02.533 --> 00:04:04.845
Pause the video, see if you
can figure out the nouns

00:04:04.845 --> 00:04:06.962
and the verbs.

00:04:06.962 --> 00:04:11.488
So he, well that's a person,
so that's going to be

00:04:11.488 --> 00:04:14.308
that is going to be a noun.

00:04:14.308 --> 00:04:18.616
Ate, that's an action,
that is going to be a verb.

00:04:18.616 --> 00:04:20.708
The by itself isn't a
person, place or thing

00:04:20.708 --> 00:04:23.004
but watch is, watch is a thing,

00:04:23.004 --> 00:04:25.950
so that's gonna be our noun.

00:04:25.950 --> 00:04:30.423
One more sentence, Dogs are silly.

00:04:30.423 --> 00:04:34.964
Well dogs are clearly a
thing, so that's our noun.

00:04:34.964 --> 00:04:37.808
Now the verb might be a
little bit harder to see,

00:04:37.808 --> 00:04:39.739
what's the action?

00:04:39.739 --> 00:04:42.989
Well the dogs are silly,
you can say the action

00:04:42.989 --> 00:04:44.574
they are taking is being silly,

00:04:44.574 --> 00:04:46.382
and that's just something they do.

00:04:46.382 --> 00:04:48.678
So this one might be a little
bit harder to understand.

00:04:48.678 --> 00:04:50.872
But what is the dog doing,
they're being silly.

00:04:50.872 --> 00:04:54.895
Are is the action, so
that right over there,

00:04:54.895 --> 00:04:57.414
that right over there is the verb.

00:04:57.414 --> 00:05:01.112
So hopefully this starts to
give you a hang of things

00:05:01.112 --> 00:05:02.676
and we'll look at a lot more examples.

00:05:02.676 --> 00:05:05.460
That's really the key of
understanding nouns and verbs.

00:05:05.460 --> 00:05:07.512
And we'll also start to think
about what all these other

00:05:07.512 --> 00:05:10.661
words are that we haven't labeled yet.