WEBVTT

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There's an important
distinction to make

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between cause and
effect when analyzing

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the motion of objects.

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There are two very separate
questions that we can ask.

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The first is, how does a
particular object move?

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This is a purely descriptive
geometrical question

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that we're asking.

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What does the geometry
of the motion look like?

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If we were to draw
its trajectory

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as a function of time, what's
the shape of that trajectory?

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The study of the geometry
of motion of a trajectory

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is referred to as kinematics.

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The second question we can
ask is, why does an object

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move the way it does?

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Why does the kinematic
description of the trajectory

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look the way it does?

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This concerns what the
causes are of the motion

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and of the changes
in that motion.

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The study of the cause
behind the changes of motion

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is called dynamics.

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Newton's Second Law of Motion
connects these two questions.

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When we write F equals
ma, this is more than just

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a mathematical identity.

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Physically, we're connecting
two very different questions.

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And we can symbolize that
by dividing the equation

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into its two sides.

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The right-hand
side, the ma side,

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is essentially asking
the question of how, how

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does the object move?

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What does that motion look like?

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It's a description, a
geometric description

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of the object's motion.

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The left-hand side of the
equation, where the forces are,

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answers the question of
why, why does the object

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move the way it does?

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What causes the
motion to change?

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These are very
different conceptually.

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And the remarkable thing about
Newton's Second Law, in fact,

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one of Newton's
signature accomplishments

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was to realize that
these two questions can

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be connected in this way through
Newton's Second Law of Motion.

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Since these are very
different issues,

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we'll examine them
separately in our course.

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We'll begin this week by looking
at kinematics in one and two

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dimensions, basically
learning how

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to describe the geometric
motion of an object

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and its trajectory.

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We'll follow that by discussing
the dynamics of the motion,

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examining why an object's motion
changes when forces are applied

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through a discussion of Newton's
laws and their applications.