Experiment 6



For each collision, determine the momentum and kinetic energy of each glider before and after the collision, then check to see if these quantities are conserved by comparing total values. Because of the uncertainty associated with timing measurements and other factors such as rebound elasticity, leveling, etc., numerical accuracy of 15% or less will be considered adequate for this experiment.  Ask your lab instructor if you have questions about the validity of any specific measurement.

Preliminary Set-Up


Figure 6-1.Schematic of glider and photogate set-up

♦♦♦NOTE:  DO NOT slide gliders on the track without turning on the air supply.♦♦♦

Refer to Figure 6-1 for proper arrangement of the apparatus. Complete the following items before taking data.  All data will be entered on an accompanying Worksheet.  This Worksheet also contains the necessary tables and equations to test for momentum and energy conservation.


Procedure 1 - Elastic Collision between Equal Masses; One Mass Initially at Rest.
1.  Place one glider (A) near one end of the track and a second (B) in the middle between the two photogates. (Both gliders should have bumpers pointing in the same direction -- specifically in the direction of motion.)

2.  Arm the photogates by clicking the Collect button on the LoggerPro window.

3.  Launch glider A gently but firmly such that, after the collision, glider B is displaced completely from its stationary position between the photogates. If mA and mB are approximately equal, the first glider should essentially come to rest between the photogates while glider B moves off with the same speed as A prior to the collision. In practice, the velocities will not be exactly equal because the collision is not perfectly elastic.

4.  Copy the transit times ΔtA (before the collision) and ΔtB (after the collision) from the Table Window, and enter these values in cells B22 and E29 respectively on the Worksheet.

5.  Repeat this process two more times, and enter the resulting transit times in cells B23:24 and E30:31 of the Worksheet.

Procedure 2 - Elastic Collision between Unequal Masses; One Mass Initially at Rest.
1.  For this experiment, add two weights (50 g each; 100 g total) to Glider B. Again, weigh the glider (including weights and bumper) and enter the data in cell C52 of the Worksheet.

2.  Using the lighter glider as the projectile and heavier as the target, repeat the steps in Procedure 1 to obtain three different sets of timing data for this system. In this case, you will need to record ΔtA both before and after the collision as well as ΔtB after.

NOTE:  In this situation, glider A should rebound and pass through Photogate 1 a second time (but in the opposite direction). The velocity and momentum for this glider after the collision therefore is negative. This is accounted for in the equations built into the Worksheet.
3.  Enter your timing data for this procedure where called for in cells B59:B61; B66:B68; and E66:E68 of the Worksheet.
Procedure 3 - Inelastic Collision between Equal Masses; One Mass Initially at Rest.
1.  For this experiment and the next, you will need to replace the rubber bumpers with devices that stick together when the gliders collide. This is accomplished with a needle and cork system that your lab assistant can show you. Add these items to each glider, and measure and record the revised masses in cells C94 and C96 of the Worksheet.

2.  Repeat steps 1 - 4 from Procedure 1 three times, and record your new data in cells B101:B103, B108:B110, and E108:E110 of the Worksheet.

NOTE:  In this situation gliders A and B have the same velocity after the collision because they are connected together, so the times in cells B108:B110, and E108:E110 of the Worksheet should be nearly identical. In addition, Photogate #2 will give double readings for the transit time because the coupled masses have a gap in the middle which triggers the photogate. In any case, just copy one set of numbers into the Worksheet.

Procedure 4 - Inelastic Collision between Unequal Masses; One Mass Initially at Rest.

1.  Add two 50 gram weights to glider A. Recheck the mass of each glider (including weights and cork or needle) on the pan balance, and enter the revised masses in cells C144 and C146 of the Worksheet.

2.  Using the heavier glider as the projectile and the lighter as the target, repeat Steps 1 - 4 of Procedure 1 three times to collect timing data for this situation.

3.  Enter your resulting data in cells B151:B153, B158:160, and E158:E160 of the Worksheet.