conservation of momentum ppt

CONSERVATION OF MOMENTUM

Billiards and Impulse • What happens to the speed and/or direction of the cue (white) ball after impact? The red ball? • What happens to the momentum of both? How are they related?

Momentum is conserved or maintained between billiard balls • The momentum loss of the cue(white) ball equals the momentum gained by the red ball

Conservation of momentum • If system is closed and isolated: • Momentum in the system can not be created or destroyed, only transferred

Conservation of momentum • The total amount of momentum in a isolated system is conserved • Conserved means that the momentum can be transferred from one object to another, but not lost to the system • Closed isolated system: no other factors (forces) play a significant role in the interaction. • No momentum is passed to anything outside the system

Closed systems • No truly closed, isolated systems • But lots of systems that are significantly closed and isolated to allow use of the idea of momentum conservation • Error has to be insignificant for system to be closed

Momentum is transferred whenever there is a collision Examples of collisions in real life?

Types of Collisions • Elastic: collision where kinetic energy and momentum are conserved, nothing sticks together • Inelastic: collision where only momentum is conserved, nothing sticks together • Completely Inelastic: collision where only momentum is conserved, objects stick together

Example of Elastic Collisions • There are no examples of large scale perfectly elastic collisions • Some of the kinetic energy of a moving object is converted into internal (ex. Thermal) energy of the other object involved in the collision, or converted to external TE (heating the surrounding environment)

Most common types of collisions in nature are inelastic!

Equation for Conservation of Momentum • Momentum of all objects in system before interaction = Momentum of all objects after the interaction

Conservation of Momentum equation • For 2 objects • (can be expanded by adding a term on each side of equation for each additional object) m1v1 + m2v2 = m1v1’ +m2v2’

Example problem #1 • Two Car Collision… A 1500 kg car traveling at 15 m/s to the south collides with a 4500 kg truck that is initially at rest at a stoplight. The car and the truck stick together after the collision. What is the velocity of the final two car mass?

Example Problem #2 • A hockey player shoots a 1.5 kg puck at 80 m/s that is caught by the opposing team’s 65 kg goalie. • What is the resulting velocity of the goalie, who started from rest?

Example of Conservation of momentum

SHOOTING A GUN AND RECOIL

Math behind recoil • Initial momentum of bullet and gun = 0 • The sum of the momentums of both must total 0 • Momentum of gun = -(Momentum of bullet)

Example #3 • Mr. Baker shot a 87g bullet from a 4.8 kg gun. The bullet leaves the gun at 600 m/s If both bullet and gun start from rest, what is the final velocity of the gun.

Recoil

Example of conservation of momentum

LAUNCHING A ROCKET

What force makes the rocket move upward?

How rockets move • Fuel is ignited, particles move very fast. • Particles push on the rocket • Rocket pushes back sending particles down towards Earth • The upward p of rocket = downward p of exhaust