1. Impulse and Momentum

2. Science Starter
Show mathematically why an 80,000 pound (36,000 kg) big rig traveling 2 mph (0.89 m/s) has the SAME MOMENTUM as a 4,000 pound (1,800 kg) sport utility vehicle traveling 40 mph (18 m/s).

3. Answer
Momentum is the product of an object's mass and velocity. The formula is
p = mv. The product of each is equivalent.
The SI unit for momentum is the kilogram x meter/second (kg x m/s).
Truck momentum = (36,000 kg)(0.89 m/s) = 32,000 kg x m/s
SUV momentum= (1,800 kg)(18 m/s) = 32,000 kg x m/s

4. Remember F=ma Impulse = Force * Change in Time
Momentum = Mass * Velocity

5. Throwing an egg at a Pillow vs. Wall
If their momenta are equal before the collisions (same mass and velocity), both eggs experience identical impulses because both are stopped by the collision.
The egg that hit the wall experienced the greater impact force due to the shorter impact time.
The egg that collided with the bed sheet experienced the greater time of impact, thereby experiencing a smaller stopping force over a longer time interval.
Which egg experienced the greater impulse, the egg that hit the wall or the bed sheet? (Be careful here!)
Which egg experienced the greater force of impact?
Which egg experienced the greater time of impact?

6. Car Crash
Would you rather be in a head on collision with an identical car, traveling at the same speed as you, or a brick wall?
Assume in both situations you come to a complete stop.

7. Car Crash (cont.) Everyone should vote now
Raise one finger if you think it is better to hit another car, two if it’s better to hit a wall and three if it doesn’t matter.
And the answer is…..

8. Car Crash (cont.) The answer is… It Does Not Matter! Look at FΔt= mΔv
In both situations, Δt, m, and Δv are the same! The time it takes you to stop depends on your car, m is the mass of your car, and Δv depends on how fast you were initially traveling.

9. Major Theme The shorter the impact time, the greater the force!!!
An impulse is needed to change momentum!

10. Crash Test Lab Procedure: Students work with your table partner(s)
Groups watch their assigned crash test video
Students research the necessary information to complete the worksheet
Students complete equations in order to determine the forces
Groups look up the crash test rating for their vehicle
Find your car’s rating: recalls/index.htm