Momentum Review

• What is momentum? – “mass in motion”

• What is the equation?• P=m*v

• What are the units?• Kg*m/s

Momentum Review• Is it a vector?• Yes, because it includes

velocity

• How does the equation work?• If mass increases,

momentum increases. If velocity increases, so does momentum. They’re directly proportional.

Momentum Review• If something has no motion, it has no momentum.

• Finally, if we manipulate the mass or velocity, what will happen to the momentum? • It’ll do the same

• Can objects with different masses and velocities have the same momentum?• YES

QUICK PRACTICE

1. A 1.5 kg ball is thrown at 10 m/s. What is the ball’s momentum?

2. A 2 kg ball has a momentum of 25 kg m/s. What is the ball’s speed?

3. A ball is moving at 7.0 m/s and has a momentum of 100 kg m/s. What is the ball’s mass?

QUICK PRACTICE - ANSWERS

• 1. p = 15 kg m/s • 2. v = 12.5 m/s• 3. m = 14.29 kg

Momentum is hard to stop unless you have…..

Impulse

• Impulse an action/reaction force that causes a change in momentum

• An object with momentum can be stopped or changed if a force is applied against it for a given amount of time.– the amount of time a force acts on an object is the IMPULSE

• FORMULA Impulse = Force * time– Unit – N*s

Impulse-Momentum Theorem

• Impulse = Change in momentum

• In equation form, F • t = Δ mv

• If the time of impact on an object is doubled, how is the impulse affected?

• If the time of impact on an object is extended by 4, by how much is the force of impact altered?

REAL WORLD APPLICATIONS!BASEBALL-http://www.youtube.com/watch?v=BQilXcnJD3o

CAR ACCIDENTS – “Crumple Zones” https://www.youtube.com/watch?v=zS_Gk7vjmOg“Physics of…” http://www.youtube.com/watch?v=yUpiV2I_IRI

KARATE CHOP – http://www.youtube.com/watch?v=1HNuCJ4KlYohttp://www.youtube.com/watch?v=2SkuZrU_24E

WATCH OUT FOR THAT TRAIN! - http://www.youtube.com/watch?v=LCAwRnG0yho&feature=related

GUIDED PRACTICE

F * t = m *Δ vF * 0.3 = 1400 * (15-0)

0.3 F = 21,00070,000 N East

F * t = m *Δ v3 * 1.50 = 0.5 (v)

4.5 = 0.5 v9.00 m/s to the right

F * t = m *Δ vImpulse = (0.40) (-22-18)

Impulse = -16 kg*m/s South

• A large milk truck with a mass of 5000 kg, is riding at 350.0 m/s when it suddenly slams on the brakes to avoid hitting a banana peel like in Mario Kart. The truck loses control striking other vehicles but eventually bring the truck to a stop in 25 s. What average force do the brakes exert on the truck?

F * t = m *Δ vF (25) = (5000) (350-0)25 F = 1,750,000F = 70, 000 N

• If the truck had not slammed on the brakes and had lightly pressed on them for 50 seconds. What average force would the brakes have exerted?

F * t = m *Δ vF (50) = (5000) (350-0)50 F = 1,750,000F = 35,000 N

Real – World Application?!

• Jennifer, who has a mass of 50.0 kg, is riding at 35.0 m/s in her red sports car when she must suddenly slam on the brakes to avoid hitting a deer crossing the road. She strikes the air bag, that brings her body to a stop in 0.500 s. What average force does the seat belt exert on her?

F * t = m *Δ vF (0.5) = (50) (35-0)0.5 F = 1750F = 3,500 N

• If Jennifer had not been wearing her seat belt and not had an air bag, then the windshield would have stopped her head in 0.002 s. What average force would the windshield have exerted on her?

F * t = m *Δ vF (0.002) = (50) (35-0)0.002 F = 1750F = 875,000 N

Exit Ticket How would a water balloon toss be an application of momentum and impulse?