Chapter 6 Momentum Momentum and Collisions This chapter

Momentum and Collisions • This chapter is concerned with inertia and motion. • Momentum

• Momentum = mass X velocity • p = mv • Momemtum is

Sample Questions • Which has more momentum, a 1 -ton car moving at 100

• Large Momentum Examples: ØHuge ship moving at a small velocity P =

Impulse • Newton’s Second Law can read SF = ma = m(Dv/Dt) = (Dmv)/(Dt)

Sample Question • Does a moving object have impulse? Impulse is not a property

Sample Question • Does a moving object have momentum? Yes, but recall that motion

When Force is Limited • Apply a force for a long time. Ø Examples:

Minimize the Force • To minimize force … ØIncrease Dt qcatching a ball q.

Maximize Momentum Change Apply a force for a short time. ØExamples: q. Boxing q.

• If SF = 0, then impulse = Dp = zero, or Momentum

Demonstrations • Rocket balloon • Cannon • Rocket Scooter

When can Momentum be Conserved? u. Internal forces cannot cause a change in momentum

COLLISIONS • Collisions involve forces internal to colliding bodies. • Inelastic collisions - conserve

Conserve Energy and Momentum Before Collision Case 1: Equal masses Case 2: M>M Case

Slides: 19

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Chapter 6 Momentum

Momentum and Collisions • This chapter is concerned with inertia and motion. • Momentum helps us understand collisions.

• Momentum = mass X velocity • p = mv • Momemtum is a vector

Sample Questions • Which has more momentum, a 1 -ton car moving at 100 km/hr or a 2 -ton truck moving at 50 km/hr? • Car • Truck p = mv = (1 ton)(100 km/hr) p = (2 ton)(50 km/hr)

• Large Momentum Examples: ØHuge ship moving at a small velocity P = mv ØHigh velocity bullet P = mv

Impulse • Newton’s Second Law can read SF = ma = m(Dv/Dt) = (Dmv)/(Dt) = (Dp/ Dt) Rearranging, Impulse = Dp = FDt

Sample Question • Does a moving object have impulse? Impulse is not a property of the object, but something that it can give or get from an interaction. Notice that it is not motion that gives us an impulse (v) but a change in motion (Dv).

Sample Question • Does a moving object have momentum? Yes, but recall that motion is relative, so the momentum depends on having velocity with respect to the standard of rest.

When Force is Limited • Apply a force for a long time. Ø Examples: q Follow through on a golf swing. q Pushing a car. F Dt

Make it Bounce p 1 p 2 = -p 1 Dp = p 2 - p 1 = -p 1 - p 1 = -2 p 1

Minimize the Force • To minimize force … ØIncrease Dt qcatching a ball q. Bungee jumping F Dt

Maximize Momentum Change Apply a force for a short time. ØExamples: q. Boxing q. Karate F Dt

• If SF = 0, then impulse = Dp = zero, or Momentum is conserved

Demonstrations • Rocket balloon • Cannon • Rocket Scooter

When can Momentum be Conserved? u. Internal forces cannot cause a change in momentum of the system. u. For conservation of momentum, the external forces must be zero.

COLLISIONS • Collisions involve forces internal to colliding bodies. • Inelastic collisions - conserve momentum • Totally inelastic collisions - conserve momentum and objects stick together • Elastic collisions - conserve energy and momentum

v = 10 v=0 M M v’ = 5 M Mv = 2 Mv’ v’ = ½ v M Before Collision p = Mv v’ After Collision p = 2 Mv’

Collisions Air Track Link

Conserve Energy and Momentum Before Collision Case 1: Equal masses Case 2: M>M Case 3: M<M