Download Physics 108

Impulse and
Momentum
Dr Ajay Kumar
Professor
School of Physical Education
DAVV Indore
Momentum and Collisions
This chapter is concerned with
inertia and motion. Momentum
helps us understand collisions.
Elastic Collisions - objects rebound
Inelastic Collisions - object stick
together an usually become
distorted and generate heat
Momentum
Momentum = mass  velocity

p = mv
Momentum is a vector quantity.
A large truck has more momentum
than a car moving at the same
speed because it has a greater
mass.
Which is more difficult to slow
down? The car or the large truck?
Large Momentum Examples:
– Huge ship moving at a small velocity
– High velocity bullet
Impulse
In order to change the momentum of
an object you must apply a force
over some time interval.
Impulse = Force  time interval

= Ft
Impulse and Momentum
Impulse = Change in Momentum

F Dt = mvf - mvi
Conservation of Momentum
This means that the momentum
doesn’t change.
Recall that F t = D(mv)
In this equation, F is the "external
force".
Internal forces cannot cause a
change in momentum.
Examples
Conservation of Momentum: If
there are no external forces, the
total momentum for a system
remains unchanged.
Example 1: a person sitting inside a
car pushing against the dashboard
Example 2: a bullet fired from a rifle
Example 3: a rocket in space
 m1u1 + m2u2 = m1v1 - m2v2
Coefficient of Restitution
v 2x  v1x
e
u 2x  u1x
For perfectly elastic collisions e=1.
If the two object stick together, e=0.
Otherwise 0<e<1.