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." When cue ball collides with another billiard ball initially at rest, 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. Since Momentum is a VECTOR, Each componet of momentum is individually conserved! P x and P y and P z

We also want to know about changes in momentum. Notation:initial momentump i final momentump f change in momentum  p = p f - p i Change in momentum is the result of a force!

We can rearrange F = ma to be F=m  v/  t =  p/  t  p = F  t 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.