Momentum

Case #2: Decreasing momentum in a long time means less force

If the brakes fail on your car would you rather hit a brick wall or a haystack. Momentum decreases the same- zero. A longer time decreases force. If you want the force of contact to be smaller increase the time of contact Ex. Bungee jump ◊Force decreased by long stretching time of cord

Conserved

A physical quantity remains unchanged

Formula for mass

M= P/v

Case #1: Increasing momentum

1. Increase time of impact. Ex. Cannons have long barrels to increase velocity of the ball. Exploding gunpowder (force) acts longer on cannonball 2. Increase the force Ex. Add more gun powder to cannon- increases force 3. Increase force and time of impact Ex. Hit golf ball with more force and extend time of force

Explain why a hockey goalie has lots of padding. Explain in terms of impulse (force & time) & momentum.

A hockey goalie has lots of padding because it decreases the momentum in a long time which means less force. If you increase the time, the force will decrease. Therefore, the hockey goalie won't feel as much pain with the padding.

Case #3: Decreasing momentum over short time means more force

Don't move "into" a punch. Decreased time equals more force Ex. Karate chop a stack of bricks Large impulse in a short time produces great force. "Relaxing with impulse"

Impulse Momentum Relationship

Impulse is equal to the change in the momentum of the object that the impulse acts on. Ft= ∆mv Impulse (force * time)= change in momentum (mass *velocity)

A bug splatters on a windshield of a car. Explain which undergoes the greater change in momentum. (careful!)

In any collision, there are always four quantities which are the same for both objects involved in the collision. Each object experiences the same force (Newton's third law) for the same amount of time, leading to the same impulse, and subsequently the same momentum change. Only the acceleration and the velocity change can differ for the two objects. The object with the least mass always receives the greatest velocity change and acceleration.

Law of Conservation of Momentum

In the absence of an external force, the momentum of a system remains unchanged. Momentum is conserved when no external force acts on it. Net momentum before collision=net momentum after collision. External forces required to change momentum

Momentum

Product of mass * velocity. Momentum (kg *m/s)= mass (kg) * velocity (m/s)

There are two balls of the same mass (10 kg). Before the collision, ball 1 is traveling at 5 m/s and ball 2 is at rest. When ball 1 collides with ball 2, ball 1 stops and ball 2 then begins moving at 5 m/s. Explain why this happens.

Since momentum is conserved, when the two balls collided with each other, the energy from 1 transferred into 2 and the energy from 2 transferred to 1. Also since momentum is conserved, the momentum before the collision must equal the momentum after the collision.

A large van and a small sports car roll down a hill at the same speed. Neglecting friction, at the bottom of the hill which vehicle will have more mass? More momentum? Explain your answers.

The large van has more mass, as mass never changes. The one with more momentum is the large van because it has more mass. For instance, if the van had a mass of 100 kg and the sports car has a mass of 80 kg and they both go at the speed of 15 m/s, then if you use the formula P=mv, you find that the large van has more momentum as compared to the small sports car.

Impulse

The product of the force acting on an object and the time during which it acts. In an interaction, impulses are equal and opposite. Impulse= force * time An impulse must be exerted on an object to change the momentum

Formula for Velocity

V= p/m

Inelastic collision

When objects collide and become entangled and deformed. Some KE transformed into Thermal energy (heat). Objects stick together and move as one, so masses are combined after collision (Ma)(Va) + (Mb) (Vb) before= (Ma + Mb) (V) after

Elastic Collision

When objects collide with NO lasting deformation or heat generation. Objects bounce perfectly. Objects move separately after collision Ex. Billiard balls, pool balls Ma)(Va) + (Mb) (Vb) before= (Ma) (Va) + (Mb) (Vb) after