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So we have some race
cars racing, right here.

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And I have an interesting
question to ask you.

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If we assume that these
cars are making this turn

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right over here,
that all of them

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are making this turn at
a constant speed of 100

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kilometers per hour, my
interesting question for you

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is, are these cars accelerating
while they make this turn?

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So is acceleration happening?

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And you might say, well, gee,
look, my speed was constant,

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it's not changing.

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If I looked at the
speedometer for the car

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here, if I looked at the
speedometer over here,

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it won't budge, it just stays
at 100 kilometers per hour.

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I don't have any change
in speed over time.

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And so then you
might say that you

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don't have any acceleration.

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But then you might
be saying, well,

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why would Sal even
make this video?

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And why would that question
even be interesting?

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And your second
suspicion would be true,

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because these cars
actually are accelerating

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despite having a constant speed.

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And you can pause it and
think about that for a second,

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if want to.

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But I wanted to point
this out to you,

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because in an example like this,
the difference between speed

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and velocity starts
to matter, speed

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being a scalar quantity
only having a magnitude.

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And velocity being
a vector quantity,

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being speed with a
direction, having

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a magnitude and a direction.

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And to think about-- let's
take a top view of this thing,

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and then I think it'll
become a little bit clearer

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the difference between
speed and velocity

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and why these things
are accelerating.

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So if I were to take a top
view of this racetrack--

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I'll do my best
attempt to draw it--

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so it might look
something like this.

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This is the top view.

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I could even draw
this red and white.

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So red, just to
give you the idea.

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So this is the red, and
there's some white in between.

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Obviously I'm not
drawing as many dividers

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as there are in
the actual picture,

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but it gives you an idea of
what I'm actually drawing.

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And then there's
some grass out here,

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there's some grass
over here, and then

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there's some grass over here.

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And let's focus on this orange
car and this red car right

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over here.

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And this is a top view, so this
is it's path right over here.

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And we're saying it
has a constant speed

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of 100 kilometers per hour.

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So if you think
about it's velocity,

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the magnitude of it's
velocity is constant,

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it's 100 kilometers per hour.

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But what is happening to the
direction of the velocity?

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Remember, velocity
is a vector quantity.

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It has magnitude and direction.

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So up here, when it's
starting to enter the curve,

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it's going in this direction.

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And you tend to show
vectors by arrows like this.

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And what you do is,
the arrow's going

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in the direction of the
velocity, in this case,

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and normally you would draw
the length of the arrow shows

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what is the velocity.

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The magnitude of the
velocity, I should say.

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So it's velocity's constant.

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So the length of this arrow
will always be constant.

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But as we see, it's
direction changes.

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When it's halfway
through the turn,

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it's not going in
that same direction.

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It is now going in a
different direction,

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and when it comes to
the bottom of the turn,

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it's going in a very
different direction.

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And the direction keeps changing
as long as it is turning.

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And I'm not going to
go into the math here.

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We're going to wait for the
math on this a little bit later.

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But remember, acceleration is
a change in velocity over time.

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Acceleration is equal to a
change in velocity over time,

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or we could say over
a change in time.

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And although the velocity's
magnitude is constant here,

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it's direction is changing.

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If there was no
acceleration on it,

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it's magnitude and the
direction of it's velocity

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would be constant,
and the car would just

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keep going in that direction.

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So somehow, the
car's direction is

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changing inward over
and over and over again.

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And so this is just kind
of a little bit of a trick

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question, something
for you to think about,

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we're going to discuss
the math in more

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detail in future videos.

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But what's happening here is the
cars actually are accelerating.

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And they're actually
accelerating inwards,

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and that's what's
changing inwards.

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And when I say inwards,
they're being accelerated

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towards the center of
the curve, and that's

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what's allowing their
direction to actually change.

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