Download Lecture15 - Purdue Physics

READING QUIZ
When cue ball collides with another billiard ball
initially at rest,
1. "the total momentum of the two balls is the
same as it was before."
2. "each ball has the same momentum after the
collision as it did before."
3. "each ball has the same kinetic energy after
the collision as it did before."
Momentum is a vector:
Magnitude = mass times speed = mv
Direction = same as velocity
(To be more precise, this is the linear momentum.)
Momentum is important because it can be
conserved,
just like mechanical energy.
Since Momentum is a VECTOR, Each
componet of momentum is individually
conserved!
Px and Py and Pz
We also want to know about changes in momentum.
Notation:
initial momentum pi
final momentum
change in momentum
pf
Dp = pf - pi
Change in momentum is the result of a force!
We can rearrange F = ma to be
F=m Dv/Dt = Dp/Dt
Dp = FDt
Or,
Change in momentum = Impulse.
Fig. 7.2
Fig. 7.6
Is momentum conserved?
If the net external force acting on a system of
objects is zero, the total momentum of the
system is conserved.
Fig. 7.10
What makes a rocket move?
Lecture Quiz - Question 1:
Which ball experiences a greater force?
A. Elastic
B. Perfectly inelastic.