Download Intro to Physics - Fort Thomas Independent Schools

Physics Advanced 1
Momentum and Collisions
Chapter 6
Key Terms
Momentum
Impulse
Law of Conservation of
momentum
Perfectly inelastic
collision
Perfectly elastic
collision
Impulse-Momentum Theorem
Essential Question

How is momentum conserved in collisions?
Unit Objectives
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Explain the fundamentals of momentum and impulse.
Explain how the momentum of an object can be increased
or decreased.
Explain how objects with greatly different masses can have
the same momentum.
Solve momentum problems and impulse problems, and
stopping distance problems.
Explain the relationship between impulse and change in
momentum using the impulse-momentum theorem.
Solve problems using the impulse-momentum theorem.
Explain how impulse is influenced by changes in the acting
force and the length of time the force acts.
Explain why impulse is so important to safety.
Explain the law of conservation of momentum as it relates to
a cannon firing a cannonball.
Explain the difference between elastic and inelastic collisions.
Explain how momentum is conserved in perfectly elastic and
perfectly inelastic collision.
Solve problems related to elastic and inelastic collisions.
Selected Answers to Questions
Explain how the momentum of an object can be increased or
decreased.
Momentum is increased by increases in mass and velocity (or
speed) and is decreased by decreases in mass and velocity (or
speed).
This illustrates a direct relationship between momentum and
speed and momentum and mass.
Explain how objects with greatly different masses can have the
same momentum.
Objects with greatly different masses can exhibit the same
momentum if the speed of the smaller-massed object increases
compared to the speed of the larger-massed object.
V = Mv
m
Explain why when velocity changes, momentum changes.

Momentum increases as speed increases, as shown by the
equation
p = mv.
2. Explain how impulse is influenced by changes in the acting force
and the length of time the force acts.

First assume that the impulse required to change the momentum of
a specific object is the same. Then explore what happens to the
amount of acting or impact force as the length of time of impact
changes.

For example, two eggs are dropped from the same height, one onto
a concrete floor and the other onto a thick foam pad. The impulse
for each egg is the same, yet the length of time of impact for each
differs. One egg breaks and the other does not.
o For the egg on the concrete floor, the time of impact is small,
so the force of impact is large, which causes the egg to
crack.
o For the egg on the foam pad, the time of impact is extended,
so the force of impact is reduced, which does not cause the
egg to break.
Explain why an increase in the time in which a forces acts on an
object to change its momentum is so important to safety.

The increase or extension in the time in which a force acts on an
object as the object changes momentum is important to safety
because of the reduction of impact force. If the time is long
enough, the impact force will be small enough such that damage or
injury is minimized or eliminated.
Explain the law of conservation of momentum using the example
of a cannon firing a cannonball.

The momentum of the cannon and cannonball before the firing is
zero. Since both objects are at rest, there is no momentum for
objects at rest. This means that after the cannon is fired, the
momentum of this system (cannon and cannonball) must also equal
zero. In order for this to occur, the momentum of the cannonball
that was fired must cancel out the momentum of the cannon when
it recoils.