# 112 Unit 8 Lab: Collisions

## Collisions

### Materials:

• lab sheet and writing utensil
• calculator
• Low friction tracks + 2 carts
• Sensors and software for measuring velocity of at least one of the carts

### Observation

We build crumple zones into cars, even though it means that cars are more easily “totaled” during collisions.

### Question

Why do we use crumple zones even though it means that cars are more easily “totaled” during collisions?

### Hypothesis

Provide a hypothesis about whether bouncy elastic collisions or sticky inelastic collisions will create greater forces on a cart during a collision with another cart.

### Test I

Use the velcro bumpers on the carts (or clay) so that they stick together when colliding. Measure the velocity of a cart while it collides into another cart that was stationary. You may use the accessory masses to adjust the masses of the carts however you prefer.

Record the initial velocity of the first moving cart here:___________

Record the final velocity of the two carts here:_______

Measure the mass of the first cart and record here:_________

Record the length of the collision (the time on your velocity graph during which the velocity of the cart was abruptly changing).

### Analysis I

Calculate the initial momentum of the first cart:

Calculate the final momentum of the first cart:

Calculate change in momentum of the first cart:

Use the impulse-momentum theorem and your recorded collision time to calculate the average force on the first cart:

### Test II

Now we will use the magnetic bumpers (or rubber bumpers) on the carts so that they bounce when colliding. Measure the velocity of a cart while it collides into another cart that was stationary. You may use the accessory masses to adjust the masses of the carts however you prefer.

Record the initial velocity of the first moving cart here:___________

Record the final velocity of the first cart here:_______

Measure the mass of first cart and record here:________

Record the length of the collision (the time on your velocity graph during which the velocity of the cart was abruptly changing).

### Analysis II

Calculate the initial momentum of the first cart:

Calculate the final momentum of the first cart:

Calculate the change in momentum of the first cart:

Use the impulse-momentum theorem and your recorded collision time to calculate the average force on the first cart:

### Conclusions

Which type of collision caused a greater force on the first cart?

Explain why this type of collision causes a greater force on the cart, in terms of what you learned in this lab.