Conservation of Momentum Using a Linear Track
Airtrack & blower, two light gates, wires, power supplies & timers, two long gliders, pin and plasticine attachments, two elastic band attachments, two small rectangular cards, spirit level, access to top pan balance.
(a) Setting up
1. Use the spirit level to check that the airtrack is level (adjust legs if necessary).
2. Choose the two long gliders, attach the two pieces of black rectangular card and elastic band attachments to each glider (as shown in the diagram). Measure the masses of gliders A & B WITH their attachments.
3. Measure the lengths of each of the black rectangles l a & l b (probably the same).
4. Set up the apparatus as shown above (DO NOT SWITCH ON THE AIR BLOWER), switch on the power supplies to the light gates so that a light beam is seen and so that each timer shows some sort of display. When the light beam is interrupted the timers record the time of interruption. Work out how each of the light-gate timer set ups operate. (Or ask your teacher. Check that when each glider passes through each light gate the black rectangular card interrupts the light beams.
(b) Elastic collisions
5. Switch on the air blower. Gently push glider A towards glider B. Record the time that glider A interrupts light gate beam 1 (t a) and the time that glider B interrupts light gate beam 2 (t b). Glider A should have stopped after colliding with glider B.
6. Repeat step 5 twice more using different amounts of pushing force on glider A.
(c) Inelastic collisions
7. Replace the elastic band attachments with the pin and plasticine attachments. Also remove the rectangular card from glider B.
8. Switch on the air blower. Gently push glider A towards glider B. Record the time that glider A interrupts light gate beam 1 (t a) and the time that combined gliders A & B interrupts
light gate beam 2 (t b). Glider A should join with glider B at the collision.
9. Repeat step 8 twice more using different amounts of pushing force on glider A.
10. Using your timings and card length measurements, calculate the velocities (v a & v b) of the two gliders in all cases above.
11.. Calculate the momentum of the gliders in all cases above BEFORE & AFTER the collisions.
NOTE: momentum (kgm/s) = mass (kg) x velocity (m/s).
12. According to the principle of the conservation of linear momentum, the total momentum of the two gliders should be the same before and after any collision.
Present your results in such a way that shows the extent to which they support (or not) the principle of conservation of linear momentum.