WEBVTT

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Last week, we discussed
the kinematics of motion.

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How one describes the
motion of an object

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by specifying its position,
velocity, and acceleration

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as a function of time.

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This week, we will
continue by discussing

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the dynamics of motion.

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How the application
of forces on an object

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changes the geometry or
trajectory of its motion.

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We will see that the applied
forces and the change

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in trajectory are related
through Newton's laws

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of motion.

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We will begin by reviewing
Newton's three laws of motion.

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These were a
landmark achievement

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in scientific thought.

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Most people who
haven't studied physics

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tend to intuitively think in
terms of the ancient mechanics

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of Aristotle in which an applied
force is required to maintain

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a body in uniform motion.

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Superficially,
this seems to agree

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with our everyday
experience, but only

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because friction plays
such an important role

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in our everyday life.

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One of Newton's
great insights was

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that applied forces cause
changes in an object's motion,

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rather than being necessary
to maintain uniform motion.

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Newton's laws were
the end result

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of a great deal of
careful definition,

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observation, and reasoning
by many scientists

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up to and including Newton.

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It is a fascinating
and compelling chapter

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in the history of science,
but we will not discuss

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that history in this course.

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Instead, we will simply state
Newton's three laws of motion

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as assumed postulates or axioms
and discuss their meaning

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and application.

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Finally, we will consider
several specific examples

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of physical forces, such as
gravity, contact forces exerted

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by a solid surface, like the
so-called normal force, which

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acts perpendicular or
normal to the surface,

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and friction, which acts
parallel to the surface,

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pulling forces like
tension in a rope or chain,

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and the force exerted by a
stretched or compressed spring

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described by Hooke's law.

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Taken as a whole,
this week will show us

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how to connect the two sides of
Newton's Second Law of Motion,

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f equals ma, the
dynamics or application

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of forces on the left-hand
side and its relation

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to the kinematics, the change in
geometry of the object's motion

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or trajectory, on
the right-hand side.