Momentum

What is Momentum?

• Momentum – tendency of objects to keep going in the same direction with the same speed–Depends on mass and velocity–Has direction

• The momentum of a ball depends on its mass and velocity

• Ball B has more momentum than ball A

• The momentum of a ball depends on direction too

Question• Which has greater momentum:

a train at rest or a moving skateboard?

Conservation of Momentum

• Conservation of Momentum – momentum cannot be created or destroyed, only transferred

• p before = p after

• VIDEO

Collisions• Collision – occurs when two or

more objects hit each other

• During a collision, momentum is transferred from one object to another because Momentum is conserved.

Collisions• Elastic Collision – objects bounce

off each other

• Inelastic Collision – objects stick to each other

PracticeA 1200 kg car drives west at 25 m/s for 3 hours. What is the car’s momentum?

p=mv(1200 kg) × (25 m/s) = 30,000 [kg m/s] west

PracticeA car is traveling at a velocity of 13.5 m/s north on a straight road. The mass of the car is 1,300 kg. A motorcycle passes the car at a speed of 30 m/s. The motorcycle (with rider) has a mass of 350 kg. Calculate and compare the momentum of the car and motorcycle. p=mv for each

Car

(1300 kg) × (13.5 m/s) = 17,550 kg m/s north

Motorcycle

(350 kg) × (30 m/s) = 10,500 kg m/s north

PracticeA child is on a sled moving down a hill at 20 m/s. The combined mass of the sled and child is 100 kg. What is the momentum of the child and sled?

(100 kg) × (20 m/s) = 2,000 kg m/s downhill

PracticeA ball moving at 30 m/s has a momentum of 15 kg m/s. What is the mass of the ball?

(15 kg m/s) ÷ (30 m/s) = .5 kg