Year 2060: Education Predictions

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Language: en

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I've been asked to make
predictions for the year 2060,

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or 50 years in the future.

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And I thought I would
focus this video

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on things that I feel
pretty good about

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or things that I feel are
close to my heart and hopefully

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things that things
like the Khan Academy

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might be able to bring about.

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So the first big change I
expect in the next 50 years--

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and I actually don't think it'll
take 50 years for it to happen.

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It'll probably
happen fairly quickly

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over the next 10 years--
is that the classroom

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model fundamentally changes.

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So classroom different.

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And it's going to change
from a model like this,

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and not all classrooms
look like this.

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There are already
classrooms that

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are exploring
different types of ways

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for students to
interact with each other

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and with the professor.

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But still, in most
classrooms of the world,

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especially if you take
the introductory courses

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at most universities, you'll
see something like this.

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You'll see a professor lecturing
in some way and a bunch

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of students sitting
in rows taking notes,

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and then they'll take an
exam at the end of the term.

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In probably, frankly, 10 years,
this is going to go away,

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completely go away.

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You won't have people
passively sitting

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in lecture halls taking notes.

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So we're going to move
from a passive model,

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taking lectures completely--
and this is already

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happening to a certain
degree-- completely

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to an active, I would call it,
discovery and creative model.

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So the classroom of the future
will look something much more

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like this.

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In fact, you might not
even call it a classroom.

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You would call it a room or
some type of project room

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or something like that.

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And the general
idea is right now

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all of these resources are spent
for people to passively get

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information from a professor.

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When that is
necessary-- and there

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will be times where you want
to learn a little bit of what

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someone else discovered about
calculus or quantum physics

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or anything like that--
that'll be at your own time,

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at your own pace.

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And we can pretend like that's
happening to this gentleman

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right over there, and
maybe he's even able

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to practice some of
those core skills.

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But a bulk of the time
will be spent doing this,

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will be doing-- building
things, creating things,

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exploring things.

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And it doesn't just have to
be science and technology.

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These people look like they're
building some type of a robot.

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It could be painting a
picture or composing a sonata

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or choreographing a dance.

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Whatever it might be,
it's going to be much more

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active, discovery-based,
and creative.

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And actually, one,
I think this is

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going to happen
technologically, because a lot

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of the stuff that's happening
in this model right over here

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can start to happen
a little bit more

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efficiently through this model.

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So it frees up time for this.

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But it's also going to
be a social imperative

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that it happens.

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If you rewind a
few hundred years--

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and actually, you
don't even have

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to rewind that far--
the bulk of society

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was kind of involved in,
I'll call it physical labor.

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You had a smaller fraction that
was involved in mental labor.

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So I'll call this mental labor,
sometimes white collar jobs.

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Something like filling out your
taxes, that is mental labor.

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And you had a very small
percentage of society--

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so this is kind of
historically, and I'm even

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overstating what it is-- a very
small percentage of society

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spent in kind of
innovation, creativity,

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art, things like that.

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So art, innovation,
true science,

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true pushing the frontiers
of the human experience

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and human understanding forward.

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Now, as you get more
and more technology,

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technology, especially with
the Industrial Revolution,

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started to automate
a lot of this.

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And it also made the pie bigger.

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And so when you have kind of
an industrial society, what

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happened is the necessity
for physical labor went down.

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So you had a smaller
percentage of the population

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that needed to do
physical labor.

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The mental labor actually
grew, so more people

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can now be involved in
things like mental labor.

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And obviously, even automation
is handling some of that

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as well, but you've freed up
more people to do mental labor.

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And you've definitely
freed up a good bit more

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of resources and people that
can now do the frontier,

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pushing the envelope, the art,
the innovation, the creativity.

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Now, if we fast-forward
to the year 2060,

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I think this is going to
become an extreme form, where

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almost no physical labor
is necessarily required.

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People might like to
do it for exercise.

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So this part right over here
is going to be very, very, very

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small, especially in
developed countries.

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And hopefully by 2060, most
countries will be developed.

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Even the mental labor is going
to be taken over more and more

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by automation.

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So a lot of this is
going to be automated.

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So you're going to
need less people

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doing traditional mental labor
tasks-- filling out paperwork,

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filling out your taxes,
things like that.

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And it's going to free
up a lot of wealth

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and a lot of resources and
a lot of people's hours

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to do truly artful,
creative, innovative things.

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And so the bulk of society,
I think, by 2060, if things

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go well, will be
over here, will be

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in this kind of creative class.

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This is where most
people will sit.

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So it's actually an imperative
that our classrooms--

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one, the tools are happening
to make it possible,

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to make it feasible.

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But not only that, but it's an
imperative if society really

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is moving in this
direction-- and I

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think it is-- so that we have
as many people as possible that

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can do this research
and development,

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that can do truly
creative activity.

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Now, a corollary to this
idea that the classroom will

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be different, that people will
be working self-paced-- they'll

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be spending a lot more
time working on projects--

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is that instead of
our credentials being,

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for the most part, seat-time
based-- so right now,

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our credentials-- and
it's not 100% seat-time.

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But to a large
degree, most people

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spend 12-- actually, 13
years in K through 12.

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So that's 13 years.

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And then if you get
a college degree,

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it's expected it's going
to be another four years.

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And there are some
people who are

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able to tweak this, skip
a grade here or there.

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But for the most part,
the bulk of people

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do 13 years and then four years.

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And then what the variable
is is how well you actually

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achieved-- how well you actually
understood the material.

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So the variable-- so this
thing is relatively fixed,

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and then the variable is
your level of achievement.

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Forgot an E, achievement.

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And this right over
here is variable.

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So some people go through
the system with straight A's.

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They've really
understood everything,

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or hopefully they've understood
everything if they got straight

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A's.

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Some people have B's.

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Some people get C's.

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And that's why we have something
called a grade point average.

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It shows that variation
in achievement,

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even though everyone is kind
of in this fixed seat-time.

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What we're going
to transition to,

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especially once everyone is
learning at their own pace--

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they don't have to kind
of move together lockstep

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in these classrooms--
is you're going

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to go to an
achievement-based model

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where there are achievements
that you are trying to get to,

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and they can be multiple things.

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Part of the
achievements could be

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skills like maybe calculus
or being able to read music

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or being able to, I don't know,
understand quantum physics.

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These would all be
achievements, but you

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decide how you will learn to
master these core concepts.

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So it won't be based on you
have to spend 13 years and then

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four years going
into debt to do it.

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You could go to a
formal institution

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to learn some of
this stuff, or you

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could learn it
however you see fit.

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You might be able to be
an apprentice with someone

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and then eventually
show that you

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know quantum physics very well.

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And I can imagine these
achievements would

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be far more rigorous
than the assessments that

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are being given right now.

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They could be oral examinations.

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They could be
practical examinations.

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They could be contingent
upon you building or applying

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some of this information.

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But what's interesting about
this is now the seat-time,

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the time is variable.

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Let me write this.

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The time is now the variable.

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You can do this whenever,
wherever, however long it

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takes.

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You could even revisit
things when you're 40 or 50.

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There won't be any
artificial stopping point,

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that you are 22.

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You're a college grad.

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Now you will not learn
new things anymore.

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And what's fixed-- and
I won't call it fixed,

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because you can always get
more and more achievements.

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But the achievements will
be at a high standard.

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It's a fixed high standard.

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So that if you get this
reading music achievement,

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you really do know
how to read music,

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which is different than
some other achievements.

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If I get a C in
a calculus class,

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it's not clear that I actually
do understand calculus.

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In fact, it's not
even necessarily true

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if I got an A in
a calculus class

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whether I definitely
understand calculus.

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So fixed high standards.

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And I imagine that the
only credentials won't just

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be these kind of
subject-based credentials.

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The most important
part-- because remember,

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the emphasis here is on the
creative, on the projects.

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And in creative fields,
your real transcript

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is not your GPA.

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Your real transcript
is your portfolio

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of projects, portfolio
of work that you've done.

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So people will get
things like this

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to show that they
understand specific domains,

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but the most important part of
the transcript of the future

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will be people's
achievements-- or I

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should say, their projects.

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So maybe I made a robot that can
maybe make toast of some kind.

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Maybe I've painted a
picture, so here's a picture.

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Maybe I've written
a piece of software

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that does something
interesting, so some software.

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So what employers and other
people will really care about

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isn't just your GPA
or how much time you

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spent in a lecture hall.

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They'll say, show me the
stuff that you have actually

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built, that shows that you are
really in this creative class,

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that you can start
from scratch and create

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something new and novel.

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And I also imagine,
because we'll

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be getting so much data
while people are actually

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working on getting some
of their core skills,

00:10:05.640 --> 00:10:08.330
that you won't just even have
these, do you know calculus?

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Do you know quantum physics?

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You'll also have metrics,
how hard working were you?

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How well did you
persevere, especially maybe

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when you failed first?

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These would be, I think,
considered to be good things.

00:10:19.132 --> 00:10:20.590
And on top of that,
you could start

00:10:20.590 --> 00:10:23.420
to measure, how well
did you help others?

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So that could be another
achievement, helping others.

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When you virtually tutor people
or physically tutor people,

00:10:30.050 --> 00:10:30.680
they rate you.

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And they say, wow, that
person really did help me.

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And we can even look
at the data to see

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whether you had a statistically
significant impact

00:10:37.710 --> 00:10:39.410
on their results.

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Now, the next corollary with
this different classroom

00:10:41.950 --> 00:10:43.470
and this
achievement-based learning

00:10:43.470 --> 00:10:45.030
is I think the
role of the teacher

00:10:45.030 --> 00:10:46.290
will change dramatically.

00:10:46.290 --> 00:10:48.590
And I think it'll be
in a very powerful way.

00:10:48.590 --> 00:10:53.470
So the role of the teacher,
rather than being a lecturer

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and often giving similar
lectures from year to year

00:10:55.860 --> 00:10:57.750
and always going
at the same pace,

00:10:57.750 --> 00:11:00.060
the teacher will now
be a coach or a mentor.

00:11:00.060 --> 00:11:02.610
And anyone who's ever seen a
great football or basketball

00:11:02.610 --> 00:11:05.190
coach will tell you that
a great coach or a mentor

00:11:05.190 --> 00:11:09.120
is a very rich and
important role,

00:11:09.120 --> 00:11:11.280
and so I think that
the role of the teacher

00:11:11.280 --> 00:11:14.820
will go up dramatically.

00:11:14.820 --> 00:11:17.820
And it actually won't even be
an isolated profession anymore.

00:11:17.820 --> 00:11:19.820
Right now, in a
traditional classroom,

00:11:19.820 --> 00:11:22.815
because it's lecture-based,
you have a classroom of 20,

00:11:22.815 --> 00:11:25.450
25, 30 students,
another classroom of 20,

00:11:25.450 --> 00:11:28.270
25, 30 students,
another classroom of 20,

00:11:28.270 --> 00:11:30.040
25, 30 students.

00:11:30.040 --> 00:11:34.830
And in each of them,
you'll have a teacher,

00:11:34.830 --> 00:11:36.600
often at the front
of the classroom,

00:11:36.600 --> 00:11:39.170
running class,
lecturing in some way.

00:11:39.170 --> 00:11:41.420
Because every student is now
working at their own pace

00:11:41.420 --> 00:11:43.169
at their own time and
the teachers are now

00:11:43.169 --> 00:11:45.940
spending most of their time
interacting with students,

00:11:45.940 --> 00:11:47.780
I could imagine a
world where, why

00:11:47.780 --> 00:11:49.590
have these walls
between classrooms?

00:11:49.590 --> 00:11:52.200
Why not just have
one larger classroom?

00:11:52.200 --> 00:11:54.980
Now it's 70, 75, 90 students.

00:11:54.980 --> 00:11:58.870
And all three teachers
work together.

00:11:58.870 --> 00:12:01.990
And so the teachers aren't
isolated in their rooms.

00:12:01.990 --> 00:12:05.160
They're all able to tag team and
play to each other's strengths.

00:12:05.160 --> 00:12:07.340
And the students will
have the benefit-- instead

00:12:07.340 --> 00:12:11.410
of having the benefit of
one, I guess, experience

00:12:11.410 --> 00:12:13.220
base and knowledge
set, the students

00:12:13.220 --> 00:12:16.210
have the experience base
of all of these teachers.

00:12:16.210 --> 00:12:18.730
And not only that, they'll
also be tutoring each other.

00:12:18.730 --> 00:12:21.490
So in this model, it's
all going from the teacher

00:12:21.490 --> 00:12:23.990
to the student.

00:12:23.990 --> 00:12:28.050
Here, it's going from
teachers to multiple students

00:12:28.050 --> 00:12:30.990
and from students to students
and maybe even students

00:12:30.990 --> 00:12:32.190
to teachers.

00:12:32.190 --> 00:12:36.190
So it's going from peer to
peer and multiple teachers

00:12:36.190 --> 00:12:37.620
to multiple peers.

00:12:37.620 --> 00:12:39.290
And I think in this
type of a model--

00:12:39.290 --> 00:12:41.873
because the teacher's going to
become that much more valuable,

00:12:41.873 --> 00:12:44.110
because now it is
all interactive.

00:12:44.110 --> 00:12:45.680
There is no more
passive lecture.

00:12:45.680 --> 00:12:48.180
There is no giving the
same lecture every year.

00:12:48.180 --> 00:12:51.530
I think that the
profession of teaching

00:12:51.530 --> 00:12:53.550
will become even
more prestigious.

00:12:53.550 --> 00:12:56.892
So my big-- and I'm
saying 2060, but I

00:12:56.892 --> 00:12:59.350
think this is going to happen
over the next 10 to 15 years.

00:12:59.350 --> 00:13:02.350
So I think by 2020
or 2025 you're

00:13:02.350 --> 00:13:04.100
going to have-- the
teaching profession is

00:13:04.100 --> 00:13:08.350
going to become at parity
with professions like medicine

00:13:08.350 --> 00:13:11.180
or law or engineering in
terms of how much of a teacher

00:13:11.180 --> 00:13:14.040
can make and how they
are valued by society.

00:13:14.040 --> 00:13:16.680
So I predict in this
reality teachers, based

00:13:16.680 --> 00:13:18.550
on today's money if you
inflation-adjust it,

00:13:18.550 --> 00:13:23.122
are going to make $150,000
to $200,000 per year.

00:13:23.122 --> 00:13:24.580
And for any of
those who say, wait,

00:13:24.580 --> 00:13:28.470
where's the money for
$150,000 to $200,000 per year,

00:13:28.470 --> 00:13:30.770
you just should realize
that right now most states--

00:13:30.770 --> 00:13:32.550
even if you just focus
on public schools--

00:13:32.550 --> 00:13:38.400
are spending on the order
of $10,000 a student.

00:13:38.400 --> 00:13:41.340
And even if you had a 25 to
one student to teacher ratio,

00:13:41.340 --> 00:13:44.870
that means that you have--
so if you multiply it

00:13:44.870 --> 00:13:51.380
by 25 students, that means you
have $250,000 for the teacher

00:13:51.380 --> 00:13:54.030
and the facilities and
any other technology.

00:13:54.030 --> 00:13:56.970
And all I'm arguing
for is that the master

00:13:56.970 --> 00:13:58.840
teachers, the ones
that are really

00:13:58.840 --> 00:14:00.770
pushing the envelope
here, should

00:14:00.770 --> 00:14:02.910
get a bulk of these
resources, as opposed

00:14:02.910 --> 00:14:06.360
to layers of bureaucracy
and whatever else.

00:14:06.360 --> 00:14:08.166
Now, the last prediction
I'll make related

00:14:08.166 --> 00:14:09.790
to education right
over here-- and it's

00:14:09.790 --> 00:14:13.720
related to all of this--
is because the actual cost

00:14:13.720 --> 00:14:15.500
of delivering a lot
of the core material,

00:14:15.500 --> 00:14:17.880
a lot of the core
practice, over here

00:14:17.880 --> 00:14:20.960
is going to go close to zero,
because you'll really just need

00:14:20.960 --> 00:14:24.357
an internet connection and
maybe your peers who are also

00:14:24.357 --> 00:14:25.440
learning alongside of you.

00:14:25.440 --> 00:14:27.200
And it'll become
even better if you

00:14:27.200 --> 00:14:29.890
have a really
amazing, experienced,

00:14:29.890 --> 00:14:31.650
professional teacher with you.

00:14:31.650 --> 00:14:35.210
But the fourth part
of it is I believe

00:14:35.210 --> 00:14:38.940
we're going to get to a
99% global literacy rate,

00:14:38.940 --> 00:14:42.070
and we're already close to this
in much of the developed world.

00:14:42.070 --> 00:14:44.980
But in the developing world,
it's significantly below this.

00:14:44.980 --> 00:14:46.650
And obviously, you
can imagine if we

00:14:46.650 --> 00:14:48.810
do get to this type
of a literacy rate

00:14:48.810 --> 00:14:52.832
what that means for health care,
what that means for population,

00:14:52.832 --> 00:14:54.540
what that means for
economic growth, what

00:14:54.540 --> 00:14:55.400
that means for wars.

00:14:55.400 --> 00:14:59.060
I think this is a very,
very, very positive thing.

00:14:59.060 --> 00:15:02.380
And coinciding with this idea
that students around the world

00:15:02.380 --> 00:15:05.360
are able to get access to
a world-class education,

00:15:05.360 --> 00:15:09.530
that it's like having clean
drinking water or electricity,

00:15:09.530 --> 00:15:13.570
I think you start getting closer
to a global meritocracy, where

00:15:13.570 --> 00:15:16.250
that student who, right
now she might just

00:15:16.250 --> 00:15:19.830
be the daughter of beggars
in some part of the developed

00:15:19.830 --> 00:15:22.510
world, but because she has
access to this material

00:15:22.510 --> 00:15:25.260
and she can develop herself--
and people will know how she's

00:15:25.260 --> 00:15:27.940
developing herself, because all
the data is being logged-- we

00:15:27.940 --> 00:15:30.540
can say, wow, she
has the potential

00:15:30.540 --> 00:15:33.740
to really be one of the
leaders in this creative class.

00:15:33.740 --> 00:15:37.270
She has the potential to
find the cure for cancer

00:15:37.270 --> 00:15:40.460
or find a new way
of doing X, Y, or Z.

00:15:40.460 --> 00:15:45.880
And so you really can give these
students all over the world

00:15:45.880 --> 00:15:48.630
the opportunities that
they really should have.

00:15:48.630 --> 00:15:50.950
And hopefully there will
be a ton of opportunities,

00:15:50.950 --> 00:15:53.560
because the pie will have
gotten so much bigger that we

00:15:53.560 --> 00:15:57.430
can support a lot of
these creative endeavors.


Energy inputs for tilling a hectare of land

WEBVTT
Kind: captions
Language: en

00:00:00.620 --> 00:00:03.460
In the last video, we talked
about how humans, over time,

00:00:03.460 --> 00:00:06.850
have gotten better and better
at getting more calories out

00:00:06.850 --> 00:00:08.660
of a given unit of land.

00:00:08.660 --> 00:00:10.600
And one thing I do
want to emphasize,

00:00:10.600 --> 00:00:12.760
in the last video, these
numbers that I came up

00:00:12.760 --> 00:00:15.650
with-- I picked these numbers
to make the math fairly simple--

00:00:15.650 --> 00:00:17.280
and to give you
the general idea.

00:00:17.280 --> 00:00:20.220
I don't want you to
think that the most

00:00:20.220 --> 00:00:23.980
that a square kilometer
can support today

00:00:23.980 --> 00:00:26.200
is exactly 1,000 people.

00:00:26.200 --> 00:00:28.840
It depends, hugely, on
what the land is like.

00:00:28.840 --> 00:00:31.630
How much of the land you're
actually using for agriculture.

00:00:31.630 --> 00:00:34.170
What crops you're
planting, et cetera.

00:00:34.170 --> 00:00:35.530
How the people are living.

00:00:35.530 --> 00:00:37.230
How many calories they need.

00:00:37.230 --> 00:00:38.949
The whole point
of the last video

00:00:38.949 --> 00:00:40.990
was just to give you a
framework that, wow, there

00:00:40.990 --> 00:00:44.360
is this upper bound based on how
much productivity you actually

00:00:44.360 --> 00:00:46.152
get from the land.

00:00:46.152 --> 00:00:48.360
Now, what we want to think
about in this video-- that

00:00:48.360 --> 00:00:50.630
was-- the last video was
this axis right here,

00:00:50.630 --> 00:00:52.450
getting more and
more out of the land.

00:00:52.450 --> 00:00:55.520
What I want to think about in
this video is, how did humans,

00:00:55.520 --> 00:00:57.170
through different
technologies, how

00:00:57.170 --> 00:01:00.040
did we get by doing less
and less of the labor

00:01:00.040 --> 00:01:02.400
for getting those
calories out of the land?

00:01:02.400 --> 00:01:04.995
Obviously, you just don't have
land and thing spontaneously

00:01:04.995 --> 00:01:07.120
grow-- well, I guess that
would happen in the wild.

00:01:07.120 --> 00:01:08.620
But if you're doing
agriculture, you

00:01:08.620 --> 00:01:10.590
need to put some
energy into the land.

00:01:10.590 --> 00:01:12.390
You've got to work the land.

00:01:12.390 --> 00:01:14.800
And so what we have
over here in this chart,

00:01:14.800 --> 00:01:17.280
and this chart is
derived from information

00:01:17.280 --> 00:01:19.450
from this book right over here.

00:01:19.450 --> 00:01:22.610
This is Energy and Society.

00:01:22.610 --> 00:01:24.490
And what we want
to think about here

00:01:24.490 --> 00:01:26.450
is the different
ways that humans

00:01:26.450 --> 00:01:28.850
have gone about to till soil.

00:01:28.850 --> 00:01:31.320
So we're not even going to
think about the total process

00:01:31.320 --> 00:01:34.530
or the total energy required
to grow a certain crop.

00:01:34.530 --> 00:01:37.060
What we're just going
to focus is one step

00:01:37.060 --> 00:01:39.030
of the agricultural process.

00:01:39.030 --> 00:01:40.930
And that is tilling the soil.

00:01:40.930 --> 00:01:43.220
And in case you're like
me and you have never

00:01:43.220 --> 00:01:46.010
worked on a farm-- which,
that's one thing I would like

00:01:46.010 --> 00:01:48.830
to change one day is actually
go through that process--

00:01:48.830 --> 00:01:51.700
but tilling the soil is
kind of churning it up.

00:01:51.700 --> 00:01:53.840
So you get the nutrients
from the bottom layers

00:01:53.840 --> 00:01:55.530
to the surface.

00:01:55.530 --> 00:01:58.890
You bury all of the remains
from the last harvest.

00:01:58.890 --> 00:02:03.740
You bury all of the
weeds so that they die.

00:02:03.740 --> 00:02:05.406
And you also get
air in the soil.

00:02:05.406 --> 00:02:07.030
What it does is it
essentially prepares

00:02:07.030 --> 00:02:10.880
the soil for the next
agricultural cycle.

00:02:10.880 --> 00:02:12.920
So it's a process
that humans have

00:02:12.920 --> 00:02:14.649
been doing since antiquity.

00:02:14.649 --> 00:02:16.190
And what I want to
do, in this video,

00:02:16.190 --> 00:02:18.220
is think about the
different ways to do it.

00:02:18.220 --> 00:02:19.929
And how much energy
is required to do it.

00:02:19.929 --> 00:02:22.178
And we're going to think
about the energy in two ways.

00:02:22.178 --> 00:02:24.150
How much of that energy
comes from humans?

00:02:24.150 --> 00:02:25.970
And how much of
that energy comes

00:02:25.970 --> 00:02:28.350
from things other than humans?

00:02:28.350 --> 00:02:31.680
So just as an example, when
we talk about human power,

00:02:31.680 --> 00:02:33.420
we're talking about
someone literally

00:02:33.420 --> 00:02:35.270
hand-plowing this field.

00:02:35.270 --> 00:02:37.500
So this woman right
over here is literally--

00:02:37.500 --> 00:02:40.690
she has this little cart that's
digging up the soil behind her.

00:02:40.690 --> 00:02:42.440
When we talk about
oxen power, we're

00:02:42.440 --> 00:02:45.510
talking about the oxen
doing most of the work.

00:02:45.510 --> 00:02:47.620
They're the ones dragging
this plough which

00:02:47.620 --> 00:02:49.320
is digging up all of the soil.

00:02:49.320 --> 00:02:52.210
And this gentleman has
to be there to supervise.

00:02:52.210 --> 00:02:55.890
But this still is
fairly intense labor

00:02:55.890 --> 00:02:58.720
that this gentleman is
doing right over here.

00:02:58.720 --> 00:03:00.462
And then, when we
talk about tractors,

00:03:00.462 --> 00:03:02.170
we're talking about
a scenario like this.

00:03:02.170 --> 00:03:05.510
Where the tractor is doing most
of the work of actually digging

00:03:05.510 --> 00:03:07.230
up, dragging this
plow behind it,

00:03:07.230 --> 00:03:09.510
and digging up all of the soil.

00:03:09.510 --> 00:03:11.744
And from this book
right over here,

00:03:11.744 --> 00:03:13.160
that's where we
got these numbers.

00:03:13.160 --> 00:03:14.951
I'll tell you which
numbers I got from them

00:03:14.951 --> 00:03:19.030
and which numbers I reasoned
through, because I wasn't fully

00:03:19.030 --> 00:03:21.010
comfortable with the
numbers that they had.

00:03:21.010 --> 00:03:22.790
But these are their numbers.

00:03:22.790 --> 00:03:27.270
That, if you are human power,
to till one hectare of soil,

00:03:27.270 --> 00:03:28.910
it'll take 400 hours.

00:03:28.910 --> 00:03:31.960
Oxen power-- and this
should be a pair not a pari.

00:03:31.960 --> 00:03:34.570
That should be a pair
of oxen, 65 hours.

00:03:34.570 --> 00:03:36.910
A 6-horsepower
tractor, 25 hours.

00:03:36.910 --> 00:03:39.344
A 50-horsepower
tractor, four hours.

00:03:39.344 --> 00:03:40.760
And in case you
all are wondering,

00:03:40.760 --> 00:03:45.070
what is a hectare of soil, it
is literally a plot of land.

00:03:45.070 --> 00:03:46.834
A hectare of soil.

00:03:46.834 --> 00:03:47.500
Let me write it.

00:03:47.500 --> 00:03:53.250
A hectare of land
is a plot of land

00:03:53.250 --> 00:03:57.590
that is 100 meters
by 100 meters.

00:03:57.590 --> 00:04:03.190
And it's roughly equal to 2 1/2
acres, not exactly 2 1/2 acres.

00:04:03.190 --> 00:04:04.560
It's like 2.4.

00:04:04.560 --> 00:04:08.950
I think 2.47 something,
but roughly 2 1/2 acres.

00:04:08.950 --> 00:04:12.820
So we're just thinking about
how many hours to essentially

00:04:12.820 --> 00:04:17.767
dig up all the soil for plot
of land 100 by 100 meters.

00:04:17.767 --> 00:04:19.350
So what we have over
here, so clearly,

00:04:19.350 --> 00:04:20.829
human takes a lot longer.

00:04:20.829 --> 00:04:22.700
Oxen, they can do a
little bit faster.

00:04:22.700 --> 00:04:24.540
6-horsepower
tractor, even faster.

00:04:24.540 --> 00:04:27.040
A 50-horsepower tractor,
very powerful tractor,

00:04:27.040 --> 00:04:28.900
even faster than that.

00:04:28.900 --> 00:04:33.100
Now, this column right
over here is the amount

00:04:33.100 --> 00:04:37.020
of energy required to
actually produce and maintain

00:04:37.020 --> 00:04:38.590
the machinery used.

00:04:38.590 --> 00:04:40.430
So this is a very
unintuitive thing.

00:04:40.430 --> 00:04:43.170
Whenever you think about--
for example, whenever

00:04:43.170 --> 00:04:44.790
you think about the
amount of energy

00:04:44.790 --> 00:04:48.140
to plow this land over
here, you tend to think, OK.

00:04:48.140 --> 00:04:49.990
Well, this individual
is going to have

00:04:49.990 --> 00:04:51.445
to expend a lot of her energy.

00:04:51.445 --> 00:04:53.570
You don't think about the
amount of energy required

00:04:53.570 --> 00:04:55.640
to actually maintain the tool.

00:04:55.640 --> 00:04:59.110
To one, build the tool that
she's using, in this case,

00:04:59.110 --> 00:04:59.940
a hand plow.

00:04:59.940 --> 00:05:02.650
And then, to maintain
that as she does it.

00:05:02.650 --> 00:05:06.410
And so this estimate-- and I
got these two from these fellows

00:05:06.410 --> 00:05:09.440
right over here, or, actually,
one of them might be a gal.

00:05:09.440 --> 00:05:11.990
But it's about
6,000 kilocalories.

00:05:11.990 --> 00:05:13.210
And this is k.

00:05:13.210 --> 00:05:15.740
This is kilocalories
for lowercase c.

00:05:15.740 --> 00:05:18.220
And one thing I want
to emphasize here,

00:05:18.220 --> 00:05:24.060
one kcal is equal to, is the
same thing as one calorie

00:05:24.060 --> 00:05:27.950
with a capital C, which
is the same thing as 1,000

00:05:27.950 --> 00:05:30.820
calories with a lowercase c.

00:05:30.820 --> 00:05:33.180
And we talked about
this in the last video.

00:05:33.180 --> 00:05:36.240
But when people talk
about food calories,

00:05:36.240 --> 00:05:39.394
they're really talking about
a calorie with a capital C.

00:05:39.394 --> 00:05:41.560
Or you could say they're
talking about kilocalories.

00:05:41.560 --> 00:05:43.450
So your candy bar,
200 calories, they're

00:05:43.450 --> 00:05:45.281
talking about this
right over here.

00:05:45.281 --> 00:05:47.780
In chemistry class, when you
talk about the amount of energy

00:05:47.780 --> 00:05:50.520
to raise a gram of water
one degree Celsius,

00:05:50.520 --> 00:05:52.550
you're talking about
these calories here.

00:05:52.550 --> 00:05:55.150
So in all of these numbers in
this chart right over here,

00:05:55.150 --> 00:05:56.770
they are in either--
you can either

00:05:56.770 --> 00:06:00.799
view as this unit, kcals,
kilocalories, or calories

00:06:00.799 --> 00:06:02.340
with a capital C.
They're essentially

00:06:02.340 --> 00:06:04.590
the same units that we
used in the last video.

00:06:04.590 --> 00:06:06.215
And these are the
same numbers that you

00:06:06.215 --> 00:06:09.770
are used to from a dietary
calorie point of view.

00:06:09.770 --> 00:06:12.630
So for example, 6,000
calories, that's

00:06:12.630 --> 00:06:16.780
about how much of a typical
male would expend in three days.

00:06:16.780 --> 00:06:20.830
So this is to maintain it over
the course of these 400 hours,

00:06:20.830 --> 00:06:22.890
in the case of the hand plow.

00:06:22.890 --> 00:06:28.130
And the total amount
of calories that

00:06:28.130 --> 00:06:30.310
were needed to make
the plow divided

00:06:30.310 --> 00:06:32.050
by the total number of hours.

00:06:32.050 --> 00:06:34.930
So whatever fraction of the
plow's life is being used here,

00:06:34.930 --> 00:06:36.520
you use that fraction
right over here

00:06:36.520 --> 00:06:38.810
to put this 6,000 calories.

00:06:38.810 --> 00:06:41.410
But needless to say,
for at least the plow,

00:06:41.410 --> 00:06:44.980
for either the human
or the oxen scenario,

00:06:44.980 --> 00:06:47.965
this isn't a significant
amount of the total calories.

00:06:47.965 --> 00:06:49.590
So obviously, if
you're doing it either

00:06:49.590 --> 00:06:52.570
with human or oxen power,
you're not using any gasoline.

00:06:52.570 --> 00:06:54.370
You're not using any petroleum.

00:06:54.370 --> 00:06:56.030
In all of these
scenarios, we're going

00:06:56.030 --> 00:06:59.700
to assume that someone has
10 working hours in the day.

00:06:59.700 --> 00:07:02.920
And that right over
here, this is a measure

00:07:02.920 --> 00:07:05.130
of how hard that
person's work is.

00:07:05.130 --> 00:07:07.250
And I estimated
these numbers here.

00:07:07.250 --> 00:07:10.340
They're slightly different than
what the original numbers were

00:07:10.340 --> 00:07:12.490
in this book right over here.

00:07:12.490 --> 00:07:13.620
But we're saying, look.

00:07:13.620 --> 00:07:17.040
If you are actually walking
along using this hand plow,

00:07:17.040 --> 00:07:20.780
that is actually very,
very vigorous activity.

00:07:20.780 --> 00:07:25.580
So it is going to require
about 400 calories per hour

00:07:25.580 --> 00:07:27.370
to do this type of activity.

00:07:27.370 --> 00:07:28.890
You do it over 10 hours.

00:07:28.890 --> 00:07:31.430
It's going to require
4,000 calories just

00:07:31.430 --> 00:07:32.795
to do that over 10 hours.

00:07:32.795 --> 00:07:34.795
And then, we're assuming
that there's some rest.

00:07:34.795 --> 00:07:36.750
That the rest of the day,
you're going to walk around.

00:07:36.750 --> 00:07:38.430
And maybe you're going to
cook dinner, eat breakfast.

00:07:38.430 --> 00:07:39.805
You're going to
sleep some of it.

00:07:39.805 --> 00:07:41.930
We're assuming that the
other 14 hours a day

00:07:41.930 --> 00:07:45.270
are going to be at about
100 calories per hour.

00:07:45.270 --> 00:07:46.710
And so this is the total.

00:07:46.710 --> 00:07:48.820
If someone were to,
using this technique,

00:07:48.820 --> 00:07:51.090
work for a total
of 10 hours, this

00:07:51.090 --> 00:07:53.730
is how many calories they
would consume in the day.

00:07:53.730 --> 00:07:56.104
And you can see, this is
the most labor-intensive.

00:07:56.104 --> 00:07:57.770
So it looks like that
they would consume

00:07:57.770 --> 00:07:59.880
the most calories per day.

00:07:59.880 --> 00:08:01.620
These two are the
least labor-intensive.

00:08:01.620 --> 00:08:03.578
You're sitting on a
tractor although that still

00:08:03.578 --> 00:08:06.270
requires more calories than
sleeping or watching TV,

00:08:06.270 --> 00:08:08.960
and so that's the number of
calories they would consume.

00:08:08.960 --> 00:08:10.460
Now, this right
over here-- and this

00:08:10.460 --> 00:08:11.870
is the interesting
number, or one

00:08:11.870 --> 00:08:13.850
of the really interesting
numbers-- based

00:08:13.850 --> 00:08:15.540
on all of these
assumptions, this

00:08:15.540 --> 00:08:18.330
is the total human
input in calories

00:08:18.330 --> 00:08:23.180
to do this task, to till
this one hectare of soil.

00:08:23.180 --> 00:08:26.680
So over here, you're using
5,400 calories a day.

00:08:26.680 --> 00:08:28.103
If you're working
10 hours per day

00:08:28.103 --> 00:08:30.610
and it requires 400
total hours, you're

00:08:30.610 --> 00:08:34.386
going to be working 40
days, 400 divided by 10.

00:08:34.386 --> 00:08:38.470
40 days times 5,400
calories per day.

00:08:38.470 --> 00:08:42.190
It's going to take a human--
just the human part, not even

00:08:42.190 --> 00:08:44.080
thinking about
the 6,000 calories

00:08:44.080 --> 00:08:47.060
necessary to maintain and
make that plow-- the human

00:08:47.060 --> 00:08:51.890
is going to spend to
216,000 calories to till,

00:08:51.890 --> 00:08:55.120
to plow that one
hectare of land.

00:08:55.120 --> 00:08:57.901
And if you add the other
6,000 in for the actual plow--

00:08:57.901 --> 00:08:59.900
and you could debate what
this number should be,

00:08:59.900 --> 00:09:02.210
but it's not a significant
number compared to this--

00:09:02.210 --> 00:09:05.850
you get about 222,000
total calories.

00:09:05.850 --> 00:09:07.700
When you go to the
oxen situation,

00:09:07.700 --> 00:09:10.000
you're requiring fewer hours.

00:09:10.000 --> 00:09:14.790
And each hour, it requires
a little less calories.

00:09:14.790 --> 00:09:18.150
This is still labor-intensive,
but not as labor-intensive

00:09:18.150 --> 00:09:20.440
as what this woman right
over here is doing.

00:09:20.440 --> 00:09:23.690
So on a daily basis, using
a little bit fewer calories.

00:09:23.690 --> 00:09:26.540
But since you're only
doing 6 1/2 days of this,

00:09:26.540 --> 00:09:30.840
65 hours divided by 10,
you've significantly reduced

00:09:30.840 --> 00:09:33.830
the number of calories, the
total number of calories that

00:09:33.830 --> 00:09:37.110
the human needs to
put into this task.

00:09:37.110 --> 00:09:40.140
Now, there still is
other energy being done.

00:09:40.140 --> 00:09:42.710
And now all of a sudden, the
oxen have gotten involved.

00:09:42.710 --> 00:09:46.780
And if you assume that each oxen
consumes about 20,000 calories

00:09:46.780 --> 00:09:48.890
a day, and you have two of them.

00:09:48.890 --> 00:09:53.150
So 40,000 calories per
day just to feed the oxen.

00:09:53.150 --> 00:09:57.640
And you're going to do that for
6 1/2 days, 65 divided by 10,

00:09:57.640 --> 00:10:01.770
the oxen are going to consume
260,000 calories to do this

00:10:01.770 --> 00:10:02.650
task.

00:10:02.650 --> 00:10:06.920
So the total energy input
here, now, has gone up.

00:10:06.920 --> 00:10:08.630
So this is an
interesting phenomenon

00:10:08.630 --> 00:10:10.190
that is going on
right over here.

00:10:10.190 --> 00:10:12.370
What the human is
putting in, as we

00:10:12.370 --> 00:10:13.760
get better and
better technology,

00:10:13.760 --> 00:10:15.190
goes down substantially.

00:10:15.190 --> 00:10:18.210
216,000 to 33,000, and
we'll see with the tractor

00:10:18.210 --> 00:10:19.560
goes down even more.

00:10:19.560 --> 00:10:22.280
But the total energy, if you
include the amount of energy

00:10:22.280 --> 00:10:24.930
that the oxen have to
put in, or if you include

00:10:24.930 --> 00:10:27.110
the amount of energy
due to the gasoline that

00:10:27.110 --> 00:10:30.110
has to be used for the tractor,
the total amount of energy

00:10:30.110 --> 00:10:32.750
is going up to plow that field.

00:10:32.750 --> 00:10:35.624
But the human energy
goes down dramatically.

00:10:35.624 --> 00:10:37.540
Now, the last thing I
want to highlight here--

00:10:37.540 --> 00:10:40.710
and these are where my numbers
depart a little bit, or fairly

00:10:40.710 --> 00:10:43.680
significantly, from this
original study right over here,

00:10:43.680 --> 00:10:47.630
this original estimate--
is the machinery input

00:10:47.630 --> 00:10:49.280
on the tractors.

00:10:49.280 --> 00:10:51.960
So if you look this up, and
you could Google search it,

00:10:51.960 --> 00:10:53.640
they have much
larger numbers here.

00:10:53.640 --> 00:10:54.806
But I did a little research.

00:10:54.806 --> 00:10:57.330
And it looks like, for
most petroleum-based,

00:10:57.330 --> 00:11:01.630
combustion-based engines
or vehicles, roughly 20%

00:11:01.630 --> 00:11:05.270
of the total energy that's used
in fuel, 20% of that energy

00:11:05.270 --> 00:11:07.900
is used to for the actual
production and maintenance

00:11:07.900 --> 00:11:10.120
of that vehicle over its life.

00:11:10.120 --> 00:11:11.860
So what we did over
here is, we said, OK.

00:11:11.860 --> 00:11:14.850
For a 6-horsepower tractor--
I used their numbers--

00:11:14.850 --> 00:11:18.040
where you're going to have
to use 25 hours to do it,

00:11:18.040 --> 00:11:20.070
it's going to use
this much petroleum,

00:11:20.070 --> 00:11:24.170
assuming that it uses 23.5
liters of gas or petroleum

00:11:24.170 --> 00:11:25.684
over 25 hours.

00:11:25.684 --> 00:11:27.350
And then, I just took
20% of that number

00:11:27.350 --> 00:11:31.080
for saying, well,
how much energy

00:11:31.080 --> 00:11:33.460
had to be used to
maintain that vehicle

00:11:33.460 --> 00:11:35.630
over that amount of time?

00:11:35.630 --> 00:11:38.730
And if you think about what
fraction of this vehicle's life

00:11:38.730 --> 00:11:41.490
that 25 hours
represents, that fraction

00:11:41.490 --> 00:11:44.237
times the total amount of
energy required to produce that.

00:11:44.237 --> 00:11:46.070
So remember, these
things are made of metal.

00:11:46.070 --> 00:11:47.890
They had to be made in furnaces.

00:11:47.890 --> 00:11:51.520
So just producing a vehicle
requires a lot of energy.

00:11:51.520 --> 00:11:55.180
And so this right
over here is 20%.

00:11:55.180 --> 00:11:57.470
And I just use
that rule of thumb

00:11:57.470 --> 00:12:00.760
for most petroleum-based or
combustion-based vehicles.

00:12:00.760 --> 00:12:03.200
That 20% of the total
energy expenditure

00:12:03.200 --> 00:12:05.950
over the course of
that vehicle's life

00:12:05.950 --> 00:12:09.900
is roughly equal to
the amount of energy

00:12:09.900 --> 00:12:13.660
used to produce that vehicle.

00:12:13.660 --> 00:12:16.170
But either way, you go
all the way over here.

00:12:16.170 --> 00:12:18.240
The human has to spend
less calories sitting

00:12:18.240 --> 00:12:18.990
on the vehicle.

00:12:18.990 --> 00:12:21.170
So they spend less
calories per day.

00:12:21.170 --> 00:12:23.650
And then, the total human
input right over here,

00:12:23.650 --> 00:12:26.560
for the 6-horsepower tractor,
it's going to take them 2 1/2

00:12:26.560 --> 00:12:29.550
days-- 25 hours at
10 hours a day--

00:12:29.550 --> 00:12:32.200
is going to be 8,500 calories.

00:12:32.200 --> 00:12:34.300
But of course, you
have the petroleum used

00:12:34.300 --> 00:12:36.640
and then some estimate
of the amount of energy

00:12:36.640 --> 00:12:39.000
used to produce that tractor.

00:12:39.000 --> 00:12:41.480
And you're just taking the
fraction over that 25 hours.

00:12:41.480 --> 00:12:42.860
You're not taking
the entire life

00:12:42.860 --> 00:12:44.420
of that 6-horsepower tractor.

00:12:44.420 --> 00:12:46.350
To produce a
6-horsepower tractor,

00:12:46.350 --> 00:12:48.130
this number would be
much, much larger,

00:12:48.130 --> 00:12:50.570
if you talked about the
total number of energy.

00:12:50.570 --> 00:12:52.600
We're just taking the
small fraction of its life

00:12:52.600 --> 00:12:54.099
that we're using
it right over here.

00:12:54.099 --> 00:12:56.370
Same thing for the
50-horsepower tractor.

00:12:56.370 --> 00:12:59.750
But any way you look at
it, the human-- and this

00:12:59.750 --> 00:13:01.230
is a really interesting thing.

00:13:01.230 --> 00:13:03.410
Humans, by going
from human power

00:13:03.410 --> 00:13:05.530
all the way to a
50-horsepower tractor,

00:13:05.530 --> 00:13:08.420
you're getting almost a
factor of 200 improvement,

00:13:08.420 --> 00:13:10.310
in terms of how
little energy has

00:13:10.310 --> 00:13:12.860
to be put in by the
human to till that land.

00:13:12.860 --> 00:13:14.900
But you actually get
a total increase,

00:13:14.900 --> 00:13:19.030
if you factor in things like the
petroleum and then, definitely,

00:13:19.030 --> 00:13:22.700
the amount of energy to
actually produce that machine.

00:13:22.700 --> 00:13:25.150
So anyway, hopefully, you
found that interesting.

00:13:25.150 --> 00:13:27.820
I find this-- it's
something that you

00:13:27.820 --> 00:13:29.050
don't think a lot about.

00:13:29.050 --> 00:13:32.030
How much energy input
has to be put in?

00:13:32.030 --> 00:13:35.310
And oftentimes, we only think
about the human energy input.

00:13:35.310 --> 00:13:38.180
But we're not thinking about the
energy input from other things,

00:13:38.180 --> 00:13:40.710
like oxen.


Land productivity limiting human population

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:04.033
For us modern humans with our easy access to the local supermarket

00:00:04.033 --> 00:00:07.974
it's easy to forget that throughout human history and even today

00:00:07.974 --> 00:00:13.553
the amount of humans or human population has been limited by our ability to get calories

00:00:13.553 --> 00:00:19.144
or get human consumable food from the land, so what I want to do in this video is give us a little bit of

00:00:19.144 --> 00:00:22.729
a framework for thinking about how humans have been gathering

00:00:22.729 --> 00:00:28.102
calories from the land and how that's placed an upper limit on the number of humans

00:00:28.102 --> 00:00:32.698
that can live in any given area, or the population density of humans.

00:00:32.698 --> 00:00:38.890
So right over here you have some gentlemen looking for food, they are hunter-gatherers.

00:00:38.890 --> 00:00:45.808
I'll say HG for short, and the H part, the hunter part that they might actually find some animals.

00:00:45.808 --> 00:00:48.472
I think these guys are trying right over here are trying to trap some rabbits

00:00:48.472 --> 00:00:51.371
and the gathering part, they're just literally looking for food

00:00:51.371 --> 00:00:59.804
maybe they find fruit of some sort, or some nuts or maybe some roots that are edible by humans

00:00:59.804 --> 00:01:04.369
so literally just walk around either try to kill things or find things they can consume.

00:01:04.369 --> 00:01:08.223
So I'll call this right over here stage one.

00:01:08.223 --> 00:01:12.392
So this is hunter-gatherers, this is what most humans

00:01:12.392 --> 00:01:15.974
have done through most of human history.

00:01:15.974 --> 00:01:18.221
And just to give us a little bit of a framework

00:01:18.221 --> 00:01:20.301
for how much they could get from the land,

00:01:20.301 --> 00:01:25.062
I looked in some of the best sense of studying HG populations

00:01:25.062 --> 00:01:29.109
in land like this maybe they can get about 200 calories.

00:01:29.109 --> 00:01:35.895
I'll make this a whole column, this whole column is the amount

00:01:35.895 --> 00:01:42.722
that they can get in terms of calories per square kilometre per day.

00:01:42.722 --> 00:01:44.968
Now it's obviously going to be hugely dependent

00:01:44.968 --> 00:01:47.226
on the number of animals that live there,

00:01:47.226 --> 00:01:50.642
the type of land that's there, if they're next to a stream

00:01:50.642 --> 00:01:52.809
where maybe fish are just jumping out of the stream

00:01:52.809 --> 00:01:54.435
this number would be much higher,

00:01:54.435 --> 00:01:55.727
if they were in some type of desert

00:01:55.727 --> 00:01:57.217
this number would be much lower.

00:01:57.217 --> 00:01:59.227
But this is actually fairly in line with

00:01:59.227 --> 00:02:01.710
some of the studies of HG cultures.

00:02:01.710 --> 00:02:05.226
Now if this the number of calories that they can get

00:02:05.226 --> 00:02:06.810
from each square kilometre per day,

00:02:06.810 --> 00:02:09.306
how many humans can live in a square kilometre per day?

00:02:09.306 --> 00:02:10.975
What is the density of humans?

00:02:10.975 --> 00:02:13.813
Well, to figure that out we have know on average

00:02:13.813 --> 00:02:17.227
how many calories does a human need to survive,

00:02:17.227 --> 00:02:19.801
and for the sake of this video I'm going to make the assumption

00:02:19.801 --> 00:02:26.557
that a human being needs 2,000 calories per day

00:02:26.557 --> 00:02:29.642
to survive in a non-malnourished state.

00:02:29.642 --> 00:02:31.722
And obviously it's hugely dependent on

00:02:31.722 --> 00:02:35.055
how activ this person is or how large they are.

00:02:35.055 --> 00:02:37.550
And one other note: this whole I will be using

00:02:37.550 --> 00:02:39.477
Calories with the capital C.

00:02:39.477 --> 00:02:42.218
The Calories with the capital C are the calories

00:02:42.218 --> 00:02:44.638
that people are used to refering to when you go to the gym

00:02:44.638 --> 00:02:47.052
and you run on the treadmill and it says how many calories you've burnt

00:02:47.052 --> 00:02:50.074
or you look at the back of your candy bar and it says 200 calories.

00:02:50.074 --> 00:02:52.440
These are tha calories I'm talking about.

00:02:52.440 --> 00:02:55.526
They're slightly different notion than the calories

00:02:55.526 --> 00:02:56.969
that you encounter in your chemistry class.

00:02:56.969 --> 00:03:01.728
Those calories are calories with a lower case c.

00:03:01.728 --> 00:03:05.729
And just so that you can be optimally confused it turns out that

00:03:05.729 --> 00:03:16.453
1 Calory with an upper case C is equal to 1,000 calories with a lower case c.

00:03:16.453 --> 00:03:20.556
And the lower case c calories are the amount of energy

00:03:20.556 --> 00:03:25.136
needed to heat 1 gramme of water 1°C.

00:03:25.136 --> 00:03:27.057
So this is what you see in your chemistry class

00:03:27.057 --> 00:03:29.969
but this is not what we are going to be talking about in this video.

00:03:29.969 --> 00:03:32.141
We're talking about the capital C Calories

00:03:32.141 --> 00:03:35.143
that dietitians are always talking about.

00:03:35.143 --> 00:03:39.144
So with this assumption that the average human eats 2000 Calories a day

00:03:39.144 --> 00:03:41.971
to not get malnourished, and obviously man would eat more,

00:03:41.971 --> 00:03:45.137
women would eat less, children would eat even less,

00:03:45.137 --> 00:03:48.097
but with this assumption, what is the density of humans

00:03:48.097 --> 00:03:50.807
that could be supported by this culture right over here?

00:03:50.807 --> 00:03:56.804
Well, 200 Calories is 1 tenth of the average daily human requirement

00:03:56.804 --> 00:03:58.387
if you believe this assumption.

00:03:58.387 --> 00:04:05.305
The the population density, humans per square kilometre

00:04:05.305 --> 00:04:10.303
you can always support 1 tenth of a human with this Calory output!

00:04:10.303 --> 00:04:15.311
So you can only support 0.1 of a human per a square kilometre.

00:04:15.311 --> 00:04:18.308
So 1 human would actually need 10 square kilometres

00:04:18.308 --> 00:04:23.394
to hunt from and gather from in order to support just themselves!

00:04:23.394 --> 00:04:26.058
They would need maybe 30 or 40 square kilometres

00:04:26.058 --> 00:04:28.476
to support an entire family,

00:04:28.476 --> 00:04:30.562
so they could wander around and kill the animals

00:04:30.562 --> 00:04:33.559
and find whatever they need to find on that land.

00:04:33.559 --> 00:04:36.309
Now let's go to kind of you can view as maybe the next stage

00:04:36.309 --> 00:04:38.894
although it's now always the case that herding is going to be

00:04:38.894 --> 00:04:41.392
more productive than HG, especially with that case

00:04:41.392 --> 00:04:42.811
with the fish jumping out of the water,

00:04:42.811 --> 00:04:45.309
but let's go to the scenario right over here.

00:04:45.309 --> 00:04:51.149
So this is, we can call this a pastoral life-style.

00:04:51.149 --> 00:04:54.136
So this is 2, I'll call it pastoral.

00:04:54.136 --> 00:04:55.976
And over here is the realisation that,

00:04:55.976 --> 00:05:00.471
look, you have all of this vegetation that maybe humans can't consume

00:05:00.471 --> 00:05:03.724
but there are other animals that can consume this vegetation

00:05:03.724 --> 00:05:10.372
and they can turn those calories into calories that can be consumed by humans

00:05:10.372 --> 00:05:13.141
and, namely, the calories are themselves!

00:05:13.141 --> 00:05:14.770
So this gentleman right over here

00:05:14.770 --> 00:05:18.081
after he gets these sheep to be nice and fat,

00:05:18.081 --> 00:05:21.310
he can either eat the sheep or he can drink their milk,

00:05:21.310 --> 00:05:27.098
so one way to think about this cattle or these sheep right over here

00:05:27.098 --> 00:05:29.556
by herding them and letting them eat this grass

00:05:29.556 --> 00:05:36.100
he is turning non-human-consumable calories into human-consumable calories.

00:05:36.100 --> 00:05:38.723
And for the sake of our thought experiment let's tell we got

00:05:38.723 --> 00:05:44.470
10 time increase in the human-consumable calories per square kilometre.

00:05:44.470 --> 00:05:48.309
So now instead of 200 we're up to 2,000.

00:05:48.309 --> 00:05:56.558
And so instead of one human per square kilometre per day to support one human ...

00:05:56.558 --> 00:05:59.895
oh sorry, instead of 0.1 we can now support 1 human.

00:05:59.895 --> 00:06:02.808
So in that 10 square kilometres we can now support 10 people,

00:06:02.808 --> 00:06:06.366
in 100 square kilometres we can now support 100 people.

00:06:06.366 --> 00:06:09.224
Now the next stage - and I'm skipping a bunch of stages

00:06:09.224 --> 00:06:12.060
because we have things like subsistence agriculture

00:06:12.060 --> 00:06:15.474
and various forms that are not going to be equally productive,

00:06:15.474 --> 00:06:18.628
it depends what the land is like, it depends what tools at disposal,

00:06:18.628 --> 00:06:21.561
but the next stage that I'll just kind of jump to

00:06:21.561 --> 00:06:24.769
we can call traditional agriculture.

00:06:24.769 --> 00:06:29.298
So this right over here, let's call that traditional agriculture.

00:06:29.298 --> 00:06:34.031
And that's this one over here as well, so both of these I'm going to call traditional agriculture.

00:06:34.031 --> 00:06:36.975
For the purposes of this video the difference between

00:06:36.975 --> 00:06:39.069
traditional agriculture and modern agriculture -

00:06:39.069 --> 00:06:42.560
in traditional agriculture you didn't have mechanisation,

00:06:42.560 --> 00:06:45.562
so you had very primitive mechanisation,

00:06:45.562 --> 00:06:48.474
you definitely didn't have fossil fuel based engines,

00:06:48.474 --> 00:06:50.638
you didn't have modern pesticides,

00:06:50.638 --> 00:06:54.823
you didn't have modern genetically engineered crops,

00:06:54.823 --> 00:06:58.226
but you have some of the basic science of breeding crop

00:06:58.226 --> 00:07:01.228
and irrigating and using animals as tools.

00:07:01.228 --> 00:07:04.805
So in this stage right over here, and once again,

00:07:04.805 --> 00:07:07.637
it completely depends on where you are on the planet,

00:07:07.637 --> 00:07:10.807
how fertile the land is, how good your tools are,

00:07:10.807 --> 00:07:12.561
what crops you are actually producing.

00:07:12.561 --> 00:07:16.228
Let's assume that we've got a hundredfold increasse in the productivity.

00:07:16.228 --> 00:07:19.366
And looking in some of the historical records it looks like, it's depending on

00:07:19.366 --> 00:07:22.479
once again where you are, that's not out of the realm of possibility.

00:07:22.479 --> 00:07:28.229
So you have a hundredfold increase, so insdead of 2,000 calories per square kilometre per day

00:07:28.229 --> 00:07:33.310
you can get 200,000 calories per square kilometre per day,

00:07:33.310 --> 00:07:38.469
and now you can support 100 humans per square kilometre - if you wanna to!

00:07:38.469 --> 00:07:41.035
So you might not have 100 humans,

00:07:41.035 --> 00:07:44.142
one on all of the land, you might not be able to farm from,

00:07:44.142 --> 00:07:50.057
or there are other limits on the population for whatever they might be,

00:07:50.057 --> 00:07:53.226
but the important thing is to think about this upper bound.

00:07:53.226 --> 00:07:57.219
In this traditional you are able to get type of productivity from your land

00:07:57.219 --> 00:08:01.774
and you are able to in theory support 100 people per 1 square kilometre,

00:08:01.774 --> 00:08:04.768
that means if all of a sudden you have 200 people living there,

00:08:04.768 --> 00:08:06.765
they maybe every once migrate to this land

00:08:06.765 --> 00:08:08.432
because it seems as specially fertile

00:08:08.432 --> 00:08:10.055
or there are really small farmers living there,

00:08:10.055 --> 00:08:13.142
then all of a sudden not everyone is going to get 2,000 calories a day,

00:08:13.142 --> 00:08:16.770
some people might get malnourished, other people might actually starve.

00:08:16.770 --> 00:08:20.699
There is this upper bound on the actual number of people that can be there

00:08:20.699 --> 00:08:24.642
based on how productive the land actually is.

00:08:24.642 --> 00:08:27.224
Now let's move over to modern agriculture

00:08:27.224 --> 00:08:32.397
and we want to talk a little bit about what exactly is modern agriculture.

00:08:32.397 --> 00:08:36.475
You have machines like this combine over here

00:08:36.475 --> 00:08:38.432
that does a lot of the human labour.

00:08:38.432 --> 00:08:42.708
One human can... I'll talk about the different dimensions

00:08:42.708 --> 00:08:44.433
because there are actually two dimensions here:

00:08:44.433 --> 00:08:47.057
how much calories can you get from the land,

00:08:47.057 --> 00:08:53.058
and how much energy and labour can one human input into the land

00:08:53.058 --> 00:08:55.054
using tools at their disposal.

00:08:55.054 --> 00:08:57.891
So in this case cattle, these oxen pulling this plough,

00:08:57.891 --> 00:09:00.978
or in this case this combine that's fueled by fossil fuels.

00:09:00.978 --> 00:09:04.560
But in modern agriculture, because all of the things,

00:09:04.560 --> 00:09:07.558
you have these amazing tools, you have genetically engineered crops,

00:09:07.558 --> 00:09:11.724
you have modern pesticides and ... not everyone is a fan of all of these things,

00:09:11.724 --> 00:09:15.102
but they have hugely increased our productivity.

00:09:15.102 --> 00:09:18.363
So you have modern agriculture.

00:09:18.363 --> 00:09:21.563
Let's say that you have another factor of 10 from traditional agriculture.

00:09:21.563 --> 00:09:26.561
so now you can get 2,000,000 calories per square kilometre per day,

00:09:26.561 --> 00:09:34.149
or you can support 1,000 humans per square kilometre.

00:09:34.149 --> 00:09:38.725
So once again this right over here is an upper bound.

00:09:38.725 --> 00:09:43.305
And just to give a sense, I picked these numbers just so that nubmers would be clear

00:09:43.305 --> 00:09:46.142
I looked in some historical records, these are completely out of line

00:09:46.142 --> 00:09:49.056
with what it looks like human have been able to do in the past,

00:09:49.056 --> 00:09:53.230
but to give you a sense of what human populatin densities look like right now

00:09:53.230 --> 00:09:57.891
and why this upper bound seems to be right about correct,

00:09:57.891 --> 00:10:07.684
in a place like the U.S. the population density is 30 people per square kilometre,

00:10:07.684 --> 00:10:11.895
in a more dense country or a significantly more dense country like India

00:10:11.895 --> 00:10:17.561
the population density is 300 humans per square kilometre.

00:10:17.561 --> 00:10:21.048
And in the most population dense country in the world,

00:10:21.048 --> 00:10:25.040
which is where I come from, or actually I was born in New Orleans,

00:10:25.040 --> 00:10:27.730
but where some of my ancestors came from,

00:10:27.730 --> 00:10:32.725
which is Bangladesh, so there's a lot of people like me, I guess,

00:10:32.725 --> 00:10:41.398
Bangladesh has population density of 900 humans per square kilometre!

00:10:41.398 --> 00:10:44.816
To some degree this is a testament to the fertility of the land and whatever else,

00:10:44.816 --> 00:10:48.772
but this is pretty near the limits depending on

00:10:48.772 --> 00:10:51.768
agricultural productivity in what now on the land

00:10:51.768 --> 00:10:55.142
of modern technology, so it really makes you think

00:10:55.142 --> 00:10:56.638
if you don't get population under control,

00:10:56.638 --> 00:11:01.558
you might end up with some of these kind of hitting the wall type of scenarios.

00:11:01.558 --> 00:11:04.308
And so the last thing I want you to think about

00:11:04.308 --> 00:11:06.477
and this is why I reffered to a little bit more,

00:11:06.477 --> 00:11:09.481
is just think about those two dimensions

00:11:09.481 --> 00:11:11.640
because sometimes it get a little bit muddled.

00:11:11.640 --> 00:11:17.434
One is the kind of the productivity of land

00:11:17.434 --> 00:11:23.398
and at the other there is productivity of labour.

00:11:23.398 --> 00:11:28.895
So right over here in HG, they're not getting many calories from their land

00:11:28.895 --> 00:11:31.709
so they're right over there, and the humans have to do all the labour,

00:11:31.709 --> 00:11:34.130
they don't have animals helping them in any way,

00:11:34.130 --> 00:11:37.961
they definitely don't have robots or any types of engines helping them in any way,

00:11:37.961 --> 00:11:42.981
and so there have to spend a lot of human time and a lot of human labour

00:11:42.981 --> 00:11:45.807
doing the work, getting that productivity from the land.

00:11:45.807 --> 00:11:50.150
But as progress with things that aid humans,

00:11:50.150 --> 00:11:54.645
so for example if you all of a sudden have cattle helping you

00:11:54.645 --> 00:11:57.227
or you have other tools that help you,

00:11:57.227 --> 00:12:01.147
you get more human productivity, so less and less of human labour

00:12:01.147 --> 00:12:03.431
has to be used to get that productivity from the land

00:12:03.431 --> 00:12:05.814
so maybe other humans can do other things

00:12:05.814 --> 00:12:08.313
like paint pictures or become blacksmiths or whatever,

00:12:08.313 --> 00:12:13.145
and in this direction you get higher productivity per unit of land

00:12:13.145 --> 00:12:17.707
and so that comes from moving from HG to a pastoral life-style

00:12:17.707 --> 00:12:20.898
to traditional farming with irrigation, to modern farming.

00:12:20.898 --> 00:12:26.816
And so in this graph kind of tools for the individuals move us up,

00:12:26.816 --> 00:12:28.975
getting productivity from the land moves us right,

00:12:28.975 --> 00:12:32.226
modern argriculture gets us right over here.

00:12:32.226 --> 00:12:36.140
So we're getting mach more calories per unit land

00:12:36.140 --> 00:12:40.231
and we're getting much more calories per unit labour.

00:12:40.231 --> 00:12:44.223
So you need much smaller percentage of the human population

00:12:44.223 --> 00:12:47.226
actually involved in the farming.

00:12:47.226 --> 00:12:50.726
Anyway, I let you go there, hopefuly that gives you at least an undesrtanding

00:12:50.726 --> 00:12:53.891
of that food doesn't just come from nowhere,

00:12:53.891 --> 00:12:57.891
it really is a rate-limiting factor on humanity's population.


Viewing g as the value of Earth's gravitational field near the surface

WEBVTT
Kind: captions
Language: en

00:00:00.499 --> 00:00:03.160
What I want to do in this
video is think about the two

00:00:03.160 --> 00:00:07.030
different ways of
interpreting lowercase g.

00:00:07.030 --> 00:00:09.820
Which as we've talked about
before, many textbooks will

00:00:09.820 --> 00:00:14.430
give you as either 9.81
meters per second squared

00:00:14.430 --> 00:00:17.120
downward or towards
the Earth's center.

00:00:17.120 --> 00:00:19.410
Or sometimes it's given with
a negative quantity that

00:00:19.410 --> 00:00:22.090
signifies the direction, which
is essentially downwards,

00:00:22.090 --> 00:00:25.410
negative 9.81 meters
per second squared.

00:00:25.410 --> 00:00:27.570
And probably the
most typical way

00:00:27.570 --> 00:00:38.670
to interpret this value, as
the acceleration due to gravity

00:00:38.670 --> 00:00:47.069
near Earth's surface for
an object in free fall.

00:00:47.069 --> 00:00:49.235
And this is what we're going
to focus on this video.

00:00:56.610 --> 00:00:59.520
And the reason why I'm
stressing this last part

00:00:59.520 --> 00:01:03.280
is because we know
of many objects that

00:01:03.280 --> 00:01:05.450
are near the surface
of the Earth that

00:01:05.450 --> 00:01:06.990
are not in free fall.

00:01:06.990 --> 00:01:10.310
For example, I am near the
surface of the Earth right now,

00:01:10.310 --> 00:01:12.400
and I am not in free fall.

00:01:12.400 --> 00:01:15.720
What's happening to me right
now is I'm sitting in a chair.

00:01:15.720 --> 00:01:20.100
And so this is my chair--
draw a little stick

00:01:20.100 --> 00:01:24.150
drawing on my chair,
and this is me.

00:01:24.150 --> 00:01:25.570
And let's just
say that the chair

00:01:25.570 --> 00:01:26.970
is supporting all my weight.

00:01:26.970 --> 00:01:29.940
So I have-- my legs
are flying in the air.

00:01:29.940 --> 00:01:31.190
So this is me.

00:01:31.190 --> 00:01:32.980
And so what's
happening right now?

00:01:32.980 --> 00:01:35.850
If I were in free fall,
I would be accelerating

00:01:35.850 --> 00:01:39.500
towards the center of
the Earth at 9.81 meters

00:01:39.500 --> 00:01:40.610
per second squared.

00:01:40.610 --> 00:01:46.920
But what's happening is, all
of the force due to gravity

00:01:46.920 --> 00:01:49.810
is being completely
offset by the normal force

00:01:49.810 --> 00:01:54.810
from the surface of the
chair onto my pants,

00:01:54.810 --> 00:01:57.390
and so this is normal force.

00:01:57.390 --> 00:01:59.175
And now I'll make
them both as vectors.

00:02:03.900 --> 00:02:07.210
So the net force in my
situation-- the net force

00:02:07.210 --> 00:02:10.750
is equal to 0, especially
in this vertical direction.

00:02:10.750 --> 00:02:13.320
And because the net
force is equal to 0,

00:02:13.320 --> 00:02:16.110
I am not accelerating towards
the center of the Earth.

00:02:16.110 --> 00:02:18.340
I am not in free fall.

00:02:18.340 --> 00:02:22.630
And because this 9.81
meters per second squared

00:02:22.630 --> 00:02:24.590
still seems relevant
to my situation--

00:02:24.590 --> 00:02:26.070
I'll talk about
that in a second.

00:02:26.070 --> 00:02:29.060
But I'm not an
object in free fall.

00:02:29.060 --> 00:02:32.610
Another way to interpret this
is not as the acceleration

00:02:32.610 --> 00:02:34.226
due to gravity near
Earth's surface

00:02:34.226 --> 00:02:35.850
for an object in free
fall, although it

00:02:35.850 --> 00:02:38.960
is that-- a maybe more
general way to interpret

00:02:38.960 --> 00:02:42.830
this is the gravitational-- or
Earth's gravitational field.

00:02:42.830 --> 00:02:46.491
Or it's really the average
acceleration, or the average,

00:02:46.491 --> 00:02:47.990
because it actually
changes slightly

00:02:47.990 --> 00:02:49.830
throughout the
surface of the Earth.

00:02:49.830 --> 00:02:54.250
But another way to view this, as
the average gravitational field

00:02:54.250 --> 00:02:55.650
at Earth's surface.

00:02:55.650 --> 00:02:57.810
Let me write it
that way in pink.

00:02:57.810 --> 00:03:02.970
So the average gravitational
field-- and we'll

00:03:02.970 --> 00:03:05.060
talk about what a field
means in the physics

00:03:05.060 --> 00:03:09.670
context in a second-- the
average gravitational field

00:03:09.670 --> 00:03:14.420
at Earth's surface.

00:03:14.420 --> 00:03:16.610
And this is a little bit
more of an abstract thing--

00:03:16.610 --> 00:03:18.068
we'll talk about
that in a second--

00:03:18.068 --> 00:03:20.000
but it does help
us think about how

00:03:20.000 --> 00:03:21.760
g is related to
this scenario where

00:03:21.760 --> 00:03:24.500
I am not an object in free fall.

00:03:24.500 --> 00:03:27.750
A field, when you think of
it in the physics context--

00:03:27.750 --> 00:03:29.350
slightly more
abstract notion when

00:03:29.350 --> 00:03:31.683
you start thinking about it
in the mathematics context--

00:03:31.683 --> 00:03:33.780
but in the physics
context, a field

00:03:33.780 --> 00:03:36.020
is just something that
associates a quantity

00:03:36.020 --> 00:03:38.350
with every point in space.

00:03:38.350 --> 00:03:48.029
So this is just a quantity
with every point in space.

00:03:48.029 --> 00:03:50.320
And it can actually be a
scalar quantity, in which case

00:03:50.320 --> 00:03:52.365
we call it a scalar
field, and in which case

00:03:52.365 --> 00:03:54.080
it would just be a value.

00:03:54.080 --> 00:03:55.812
Or it could be a
vector quantity,

00:03:55.812 --> 00:03:58.020
which would be a magnitude
and a direction associated

00:03:58.020 --> 00:03:59.610
with every point in space.

00:03:59.610 --> 00:04:02.370
In which case you are
dealing with a vector field.

00:04:02.370 --> 00:04:04.840
And the reason why
this is called a field

00:04:04.840 --> 00:04:08.490
is, because at near
Earth's surface,

00:04:08.490 --> 00:04:11.770
if you give me a mass--
so for example-- actually,

00:04:11.770 --> 00:04:14.240
I don't know what my
mass is in kilograms.

00:04:14.240 --> 00:04:15.890
But if you're near
Earth's surface

00:04:15.890 --> 00:04:17.660
and you give me a
mass-- so let's say

00:04:17.660 --> 00:04:21.300
that mass right over
there is 10 kilograms--

00:04:21.300 --> 00:04:26.560
you can use g to figure out
the actual force of gravity

00:04:26.560 --> 00:04:31.090
on that object at
that point in space.

00:04:31.090 --> 00:04:34.945
So for example, if this
has a mass of 10 kilograms,

00:04:34.945 --> 00:04:36.570
then we know-- and
this right over here

00:04:36.570 --> 00:04:39.390
is the surface of the Earth, so
that's the center of the Earth.

00:04:39.390 --> 00:04:41.737
So it actually associates
a vector quantity

00:04:41.737 --> 00:04:43.320
whose magnitude,--
so its direction is

00:04:43.320 --> 00:04:45.500
towards the center of the
Earth, and the magnitude

00:04:45.500 --> 00:04:51.674
of this vector quantity is
going to be the mass times g.

00:04:51.674 --> 00:04:53.340
And you could take--
since we're already

00:04:53.340 --> 00:04:54.756
specifying the
direction, we could

00:04:54.756 --> 00:04:57.120
say 9.81 meters
per second squared

00:04:57.120 --> 00:04:58.724
towards the center of the Earth.

00:04:58.724 --> 00:05:00.140
And so in this
situation, it would

00:05:00.140 --> 00:05:07.920
be 10 kilograms times 9.81
meters per second squared.

00:05:07.920 --> 00:05:10.644
Which is 98.1.

00:05:10.644 --> 00:05:12.310
And even this I've
rounded a little bit,

00:05:12.310 --> 00:05:14.390
so it's actually
approximate number.

00:05:14.390 --> 00:05:20.570
98.1 kilogram meters
per second squared

00:05:20.570 --> 00:05:24.870
which is the unit of
force, or 98.1 newtons.

00:05:24.870 --> 00:05:26.740
And this thing might
not be in free fall,

00:05:26.740 --> 00:05:30.380
so this is why g
is relevant even

00:05:30.380 --> 00:05:33.130
in a situation where the
object isn't in free fall.

00:05:33.130 --> 00:05:36.550
g has given us the
force per unit mass--

00:05:36.550 --> 00:05:41.890
the force per mass of
gravity on an object

00:05:41.890 --> 00:05:44.960
near the surface of the Earth.

00:05:44.960 --> 00:05:46.700
Another way to think
about it-- so this

00:05:46.700 --> 00:05:50.440
is the average gravitational
field, and what it's giving

00:05:50.440 --> 00:05:54.960
is force per mass.

00:05:54.960 --> 00:05:57.570
So you give me a mass
near Earth's surface--

00:05:57.570 --> 00:05:59.350
whether it's an
object in free fall

00:05:59.350 --> 00:06:02.790
or not-- you multiply
that mass times g,

00:06:02.790 --> 00:06:05.080
because it's giving
you force per mass,

00:06:05.080 --> 00:06:08.990
and it will give you the
force of gravity acting

00:06:08.990 --> 00:06:11.330
on that object near the
surface of the Earth,

00:06:11.330 --> 00:06:12.722
whether or not
it's in free fall.

00:06:12.722 --> 00:06:14.680
So I just want to make
this little distinction,

00:06:14.680 --> 00:06:17.140
because although g
tends to be referred

00:06:17.140 --> 00:06:18.980
to this way right over here.

00:06:18.980 --> 00:06:20.750
Sometimes you might
encounter a stickler

00:06:20.750 --> 00:06:24.020
who says oh no, no, no, no,
no but g is relevant even when

00:06:24.020 --> 00:06:25.370
an object is not in free fall.

00:06:25.370 --> 00:06:28.020
You obviously can't say
that my acceleration when

00:06:28.020 --> 00:06:30.395
I'm sitting in my chair is
9.81 meters per second squared

00:06:30.395 --> 00:06:31.728
towards the center of the Earth.

00:06:31.728 --> 00:06:34.330
I am not accelerating towards
the center of the Earth.

00:06:34.330 --> 00:06:35.920
And so they'll say,
oh no, no, no, no,

00:06:35.920 --> 00:06:38.730
you can't just call
this acceleration.

00:06:38.730 --> 00:06:40.330
It is true, it is
the acceleration

00:06:40.330 --> 00:06:43.850
when an object is in free fall
near the surface of the Earth--

00:06:43.850 --> 00:06:47.780
if you don't have really air
resistance, if the net force

00:06:47.780 --> 00:06:50.040
really is the force of
gravity-- then this really

00:06:50.040 --> 00:06:52.200
would be the object's
acceleration.

00:06:52.200 --> 00:06:54.019
But it becomes
relevant, and we know

00:06:54.019 --> 00:06:56.060
most objects that we know
of aren't in free fall.

00:06:56.060 --> 00:06:58.070
Obviously, an object in free
fall doesn't stay in free fall

00:06:58.070 --> 00:06:58.569
for long.

00:06:58.569 --> 00:07:00.170
It eventually hits something.

00:07:00.170 --> 00:07:02.190
But we know that
now g is actually

00:07:02.190 --> 00:07:03.840
relevant to all objects.

00:07:03.840 --> 00:07:07.040
It tells us the force
per mass And it's

00:07:07.040 --> 00:07:08.870
tempting to call it
always acceleration--

00:07:08.870 --> 00:07:10.869
because the units
are acceleration--

00:07:10.869 --> 00:07:12.410
but even when you
talk about in terms

00:07:12.410 --> 00:07:14.784
of the gravitational field,
it's still the same quantity.

00:07:14.784 --> 00:07:19.050
It still has the exact same
units, the same magnitude,

00:07:19.050 --> 00:07:20.620
and the same
direction-- it's just

00:07:20.620 --> 00:07:22.170
a different way of viewing it.

00:07:22.170 --> 00:07:24.560
Here, acceleration for
an object in free fall.

00:07:24.560 --> 00:07:27.030
Here, something to
multiply by mass

00:07:27.030 --> 00:07:29.874
to figure out the
force due to gravity.