AP_Physics_B_-_Impulse_and_Momentum.ppt

Collisions in 2 dimensions Collisions in 2 dimensions AP Physics B Impulse and Momentum Impulse = Momentum Consider Newton’s 2nd Law and the definition of acceleration Units of Impulse: Units of Momentum: Momentum is defined as “Inertia in Motion” Ns Kg x m/s Example A 100 g ball is dropped from a height of h = 2.00 m above the floor. It rebounds vertically to a height of h= 1.50 m after colliding with the floor. (a) Find the momentum of the ball immediately before it collides with the floor and immediately after it rebounds, (b) Determine the average force exerted by the floor on the ball. Assume that the time interval of the collision is 0.01 seconds. Impulse is the Area Since J=Ft, Impulse is the AREA of a Force vs. Time graph. How about a collision? Consider 2 objects speeding toward each other. When they collide...... Due to Newton’s 3rd Law the FORCE they exert on each other are EQUAL and OPPOSITE. The TIMES of impact are also equal. Therefore, the IMPULSES of the 2 objects colliding are also EQUAL How about a collision? If the Impulses are equal then the MOMENTUMS are also equal! Momentum is conserved! The Law of Conservation of Momentum: “In the absence of an external force (gravity, friction), the total momentum before the collision is equal to the total momentum after the collision.” Several Types of collisions Sometimes objects stick together or blow apart. In this case, momentum is ALWAYS conserved. When 2 objects collide and DON’T stick When 2 objects collide and stick together When 1 object breaks into 2 objects Elastic Collision = Kinetic Energy is Conserved Inelastic Collision = Kinetic Energy is NOT Conserved Example A bird perched on an 8.00 cm tall swing has a mass of 52.0 g, and the base of the swing has a mass of 153 g. Assume that the swing and bird are originally at rest and that the bird takes off horizontally at 2.00 m/s. If the base can swing freely (without friction) around the pivot, how high will the base of the swing rise