Car Crash Video http www iihs orgiihsvideos Momentum

Car Crash Video http: //www. iihs. org/iihs/videos

Momentum, Impulse, and Collisions https: //www. youtube. com/watch? v=2 UHS 883_P 60&index =1&list=PLZHDrmpjw 4 My 5 KJXCT 2 inbz 7 p. Ov 1 lqs. Rk https: //www. youtube. com/watch? v=2 htckw. Dkug. I&list=PL ZHDrmpjw 4 My 5 KJXCT 2 inbz 7 p. Ov 1 lqs. Rk&index=4&t=0 s

Momentum (p) expresses the resistance of a body to slowing down. n related to inertia n p = mv m = mass (kg) n v = velocity (m/s) n Unit is kg m/s n

Example n A toy car has a mass of 5 kg. If it is moving at a velocity of 4 m/s, what is its momentum? Given n Unknown 20 kg • m/s Equation Substitute Solve

Your Turn What is the momentum of a 25 kg boy moving at a speed of 1. 2 m/s? n 30 kg • m/s n

Impulse (I) measures a change in momentum n To calculate multiply the average force acting on a body by the length of time the force acts. Impulse = ∆ρ = m∆v = F(∆t) n F = force (N or Newtons) n ∆t = time (s) n Unit is N s n See SLO equation sheet. n

Putting it all together… Newton’s 2 nd Law F = ma a = Δv/t F=mΔv / t F(t) = m(vf-vi) Notice impulse, on the left side, is equal to the change in momentum of an object.

Impulse

Example n An 8 N force acts upon an object for 5 seconds. What impulse is given this object? Given n 40 N • s Unknown Equation Substitute Solve

Your Turn A ball changes velocity from 20 m/s to 30 m/s. If it has a mass of 5 kg, what impulse was necessary to cause this change? 50 N·s n How long would it take a 5 N force to change the velocity of the ball? (Hint: use Impulse=F(t)) 10 s n

The Law of Conservation of Momentum In an isolated system, the total momentum does not change. Momentum is conserved in all closed systems!

There are 2 types of collisions n Elastic m 1 v 1 i + m 2 v 2 i = m 1 v 1 f + m 2 v 2 f ¨Where 1 stands for object 1, 2 stands for object 2 ¨Where i stands for initial & f stands for final Use + and – velocities to show direction.

Example… A 2 kg ball strikes another ball head on at an initial velocity of +2 m/s. If the second ball had a mass of 3 kg and was initially moving at -1 m/s, what is the final velocity of the 2 kg ball if the vf of the 3 kg ball is now +1. 33 m/s? n Define variables. Then: m 1 v 1 i + m 2 v 2 i = m 1 v 1 f + m 2 v 2 f 2 kg(2 m/s)+3 kg(-1 m/s) = 2 kg(v 1 f)+3 kg(1. 33 m/s) v 1 f = -1. 5 m/s n

There are 2 types of collisions n Inelastic m 1 v 1 i + m 2 v 2 i = (m 1 + m 2)v 1&2 f ¨Where v 1&2 f is the velocity of the two objects stuck together after the collision Use + and – velocities to show direction.

Example… A 500 kg car is driving at a velocity of 10 m/s. Another car (700 kg) hits it from behind at a velocity of 25 m/s and the two cars interlock bumpers. What is the resulting velocity of the two cars? n Define variables. Then: m 1 v 1 i + m 2 v 2 i = (m 1 + m 2)v 1&2 f n 500 kg(10 m/s)+700 kg(25 m/s) = (500 kg+700 kg)(v 1&2 f) v 1&2 f = 18. 75 m/s