Physics – Air Track Lab Online

http://oldmanhonda.com/Physics/Air_Track_Labs/Air_Track_Labs_Index.html

Momentum and Energy Collisions

Purpose:

To compare and contrast elastic and inelastic collisions.

To verify that total momentum is conserved in collisions and that total kinetic energy is conserved in elastic collisions.

Background:

The momentum of an object is the product of its mass and velocity. It is a vector quantity. Theoretically, the total momentum of a pair of objects is the same before and after any collision. This is an example of the Conservation of Momentum.

The kinetic energy of a mass = ½ m v^2. Kinetic energy is a scalar quantity which cannot be negative. Some of the total kinetic energy is usually converted to thermal energy in collisions. If no kinetic energy is converted to other forms of energy, then a collision is said to be elastic. Thus in elastic collisions, kinetic energy is conserved.

Procedure:

1. The computer will assign two carts for you to use. You may get a new set o carts by clicking on the “New Experiment” button.

2. Measure the masses of the carts and the length of the carts in SI units and record in the Data Table.

3. ELASTIC:

Make sure the collisions type is set to “elastic”, if not press the “switch collisions” button. Turn on the Air Blower and keep it on during all of the runs. Pull the spring load to the right until it clicks in place. This provides the starting thrust for cart 1. Slide cart 1 to the right until it comes in contact with the spring load. Slide cart 2 to the right so it is to the right of photogate 2. The computer will prevent you from sliding it too far to the right. Click on the release lever and set cart 1 in motion. Copy down the times noted in the photogate windows and record them in your Data Table (the time data will be erased at the start of each trial). Repeat this procedure two more times. NOTE: do no click on the “New Experiment” button between trials since a totally different set of carts will be assigned!!

Make sure you understand which times go with which cart!!

4. INELASTIC

Click on the “switch collision” button so that “inelastic” is displayed. The computer will now treat the two carts as if there was a layer of Velcro between them so when they collide, they stick together. Perform three trials following the same procedure as above. Enter the observed times in the Data Table.

NOTE: do no click on the “New Experiment” button between trials since a totally different set of carts will be assigned!!

The two carts should be treated as one during inelastic collision trials. Add their lengths together to get the length to be used in the calculations you have to perform (the gap between them is so small it will not have an effect on your results). Their time will be the sum of their individual times.

Fill in the Data Table with the results from your calculations. Show a sample calculation for each new formula.