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Momentum
Chapter 7
Momentum
Momentum – the product of the mass and
the velocity of an object (inertia in motion)
momentum = mv
Momentum is a vector quantity (it has
magnitude and direction)
A moving object can have a large
momentum if it has a large mass, a high
speed, or both
Impulse Changes Momentum
If the momentum of an object changes, either
the mass or the velocity or both change (usually
it is just the velocity)
Acceleration will usually occur, produced by a
force
How long the force acts is also important, so
both force and time are important
Impulse – product of force and time interval
during which the force acts
Impulse = FΔt
Ft = Δ(mv)
Impulse Changes Momentum
Impulse and Momentum
Bouncing
Impulses are greater when an object
bounces
The impulse required to bring an object to
a stop and then “throw it back again” is
greater than the impulse required merely
to bring the object to a stop
Rebound
Conservation of Momentum
From Newton’s Second Law we know that
to accelerate an object, a net force must
be applied
If you wish to change the momentum of an
object, exert an impulse on it
If no net force or net impulse acts on a
system, the momentum of that system
cannot change
Law of Conservation of Momentum:
In the absence of an external force, the
momentum of a system remains
unchanged
Collisions
Whenever objects collide in the absence of external
forces, the net momentum of both objects before
collision equals the net momentum of both objects
after collision
Net momentum before collision = Net momentum after collision
Elastic Collision – a collision in which colliding
objects rebound without lasting deformation or heat
generation
Inelastic Collision – a collision in which the
colliding objects become distorted and/or generate
heat
Elastic Collisions
Inelastic Collisions
Collisions Continued
Perfectly elastic collisions are not common
in the everyday world, there will almost
always be heat generation or deformation
In the microscopic world, perfectly elastic
collisions are commonplace; electrically
charged particles bounce off each other
Assignment
Read Chapter 7 (pg. 86-99)
Do #19-38 (pg. 101-102)
Appendix F #1-10 (pg. 669-670)