Ch. 9 Ch. 9 Momentum Momentum

and Its and Its Conservation Conservation

Milbank High SchoolMilbank High School

Sec. 9.1Sec. 9.1Impulse and Momentum Impulse and Momentum

• Objectives– Compare the system before and after an

event in momentum problems– Define the momentum of an object– Determine the impulse given to an

object– Recognize that impulse equals the

change in momentum of an object

MomentumMomentum• What is momentum?• The Minnesota Vikings have

momentum entering the final weeks of the season…

• Anything that is moving has momentum• Depends on what?

MomentumMomentum

• Momentum = mass * velocity • In physics, the symbol for momentum is

“p”sssooo…

• p = m * v • kg·m/s

Which has more momentum, a supertanker tied to a dock or a raindrop falling?

MomentumMomentum• Determine the momentum of a ...

– 60-kg halfback moving eastward at 9 m/s. • 60 x 9 = 540 kg·m/s east

– 1000-kg car moving northward at 20 m/s. • 1000 x 20 = 20,000 kg·m/s

– 40-kg freshman moving southward at 2 m/s. • 40 x 2 = 80 kg·m/s

Impulse and MomentumImpulse and Momentum• Impulse = Change in momentum • Impulse

– The product of the average net force exerted on an object and the time interval over which the force acts

– N•s

Real Life Applications..Real Life Applications..• Sports…

– Follow-through!– Gymnastics Mats

• Cars…– Airbags!– Before airbags….– Bumpers

• Eggs…• Jumping…

– Knees– Shoes

ReviewReview• Can a bullet have the same

momentum as a truck?

Sec. 9.2Sec. 9.2The Conservation of The Conservation of

Momentum Momentum

• Objectives– Recognize the conditions under which

the momentum of a system is conserved– Apply conservation of momentum to

explain the propulsion of rockets– Solve conservation of momentum

problems in two dimensions by using vector analysis

The Law of Conservation on The Law of Conservation on MomentumMomentum

• The total momentum of two objects before a collision is equal to the total momentum of the two objects after the collision.

Two Particle CollisionsTwo Particle Collisions– Inelastic collisionsmAvA1 + mB1vB1 = mAvA2 + mBvB2

PropulsionsPropulsions• We can also use:

pA2 = -pB2

mAvA2 = -mBvB2

Example Problem Pg. 212