For an inelastic collision between two objects,

1."the total kinetic energy of the objects changes.",

2."the total momentum of the objects changes.",

3."the total potential energy of the objects changes."

READING QUIZ

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.

We also want to know about changes in momentum.

Notation: initial momentum pi = mvi

final momentum pf = mvf

change in momentum p = pf - pi

We can rearrange F = ma to be:

p = Ft

Or,

Change in momentum = Impulse.

(Calculate force on baseball…)

If the net external force acting on a system of objects is zero, the total momentum of the system is conserved.

What makes a rocket move?

(Is mass of rocket constant? Is air needed?)

Fig. 7.14

Lecture Quiz - Question 1:

Which ball experiences a greater force?

A. Elastic

B. Perfectly inelastic.

Fig. 7.15

Fig. 7.17

Fig. 7.18

Try This Box 7.4

Question 35