Conservation of Energy Collisions Conservation of Energy
Law of conservation of momentum The total amount of momentum objects have is conserved when they collide. Momentum may be transferred from one object to another, but none is lost. The amount of momentum is the same before and after they interact. The Law of Conservation of Momentum states that “In the absence of an external force, the momentum of a system remains unchanged or conserved.”
MOMENTUM Ft Which would it be more safe to hit in a car ? Ft mv Knowing the physics helps us understand why hitting a soft object is better than hitting a hard one. Ft mv mv Ft
ways to decrease momentum EXAMPLES : Padded dashboards on cars Airbags in cars OR safety nets in circuses 4 0Flexing your knees when jumping from a higher place to the ground OR elastic cords for bungee jumping Using wrestling mats instead of hardwood floors. Dropping a glass dish onto a carpet instead of a sidewalk
collisions A collision occurs when two or more objects hit each other. During a collision, momentum is transferred from one object to another. The total momentum before = the total momentum after The 2 major types of collisions are 1) Elastic Collisions 2) Inelastic Collisions Elastic Collision Inelastic Collision
collisions
http://www.pbslearningmedia.org/asset/lsps07_int_momentum/
Elastic collision sample problem Two 0.165 kg billiard balls roll toward each other and collide head-on. Initially, the 5-ball has a velocity of 0.5 m/s. The 10-ball has an initial velocity of -0.7 m/s. The collision is elastic and the 10-ball rebounds with a velocity of 0.4 m/s, reversing its direction. What is the velocity of the 5-ball after the collision?
Inelastic collisions sample problem A train car moving to the right at 10 m/s collides with a parked train car. They stick together and roll along the track. If the moving car has a mass of 8,000 kg and the parked car has a mass of 2,000 kg, what is their combined velocity after the collision?
Car crash video http://www.youtube.com/watch?v=r8E5dUnLmh4&feature=related