Holt Physics Chapter 6: Momentum and Collisions
I.
Section 6-1: Momentum and impulse
A. Linear Momentum describes the force or energy that a
moving object carries with it. Momentum can be transferred
through collisions
B. Momentum is defined as an object’s mass multiplied by its
velocity. Momentum is a vector quantity whose sign depends
on its velocity.
Momentum
p = mv
momentum = mass x velocity
C. You can think of momentum as the force or energy needed to
stop a moving, massive object.
D. A change in momentum takes force and time
E. Impulse is a change in momentum
F. Impulse Momentum Theorem introduces the concept of time
to momentum and states simply that a force applied over a
time will change momentum due to the change in velocity.
Impulse-momentum Theorem
FΔt = Δp
or FΔt = Δp = mvf – mvi
Force x time interval = change in momentum
II.
Section 6-2: Conservation of Momentum
A. Energy is transferred in collisions (ignoring friction) and
momentum is conserved.
B. The Law of Conservation of Momentum: “The total
momentum of all objects interacting with one another remains
constant regardless of the nature of the forces between the
objects.” (p.216)
C. Momentum is also conserved for objects pushing away from
each other. In this scenario the momenta would be equal but
opposite according to Newton’s 3rd law.
D. During any collision (ignoring friction) the change in
momentum of one object is equal but opposite the change in
momentum of the other object.
E. Forces in real collisions are not constant and friction does
exist! Be Aware!
III. Section 6-3: Elastic and Inelastic Collisions
A. Perfectly Inelastic Collisions: Collisions that involve two
objects that move together after the collision (including
stationary objects) are called “perfectly inelastic”
Perfectly Inelastic Collisions
m1v1,i + m2v2,i = (m1 + m2) vf
B. Objects in an inelastic collision are deformed during the
collision and lose some kinetic energy to deformations, sound
and heat.
C. We can calculate this loss of kinetic energy using equations
from chapter 5.
D. Elastic Collisions: Collisions that involve two objects that
remain separate after the collision are called “elastic
collisions”
E. In an elastic collision both, the total momentum and the total
kinetic energy remain constant.
F. Most collisions are neither elastic nor perfectly inelastic
G. Objects in an elastic collision maintain or return to their
original shape after the collision.