Momentum: collisions on an air track sim
Load two gliders, fire them at each other in elastic, sticky or explosion collisions, time them through light gates, and show that the total momentum is the same before and after.
Forces and motion: momentum · covers the IGCSE, GCSE topic
What the sim shows
Momentum is mass × velocity, p = mv, and its direction matters: here, to the right is positive. In every collision on the track, elastic, sticky or explosion, the total momentum after equals the total before, because the only forces are the ones the gliders put on each other, equal and opposite (the air cushion carries each glider's weight, 0.2 kg × 10 N/kg = 2 N, so there is almost no friction). Kinetic energy, ½mv², is kept only in an elastic collision. Sticky gliders that join lose kinetic energy (it becomes heat and sound in the Velcro), and in an explosion the spring's stored energy becomes kinetic energy from nothing moving. Example: a 0.2 kg glider fired at 0.424 m/s into a 0.4 kg glider at rest has p = 0.0849 kg m/s. Elastic: it comes back at 0.141 m/s while the other leaves at 0.283 m/s, still 0.0849 kg m/s, with 0.0180 J of kinetic energy before and after. Each light gate times how long a 100 mm card blocks its beam, so v = 0.100 m ÷ time. The launchers are springs (k = 40 N/m): ½kx² = ½mu², so u = x√(k/m). Model limits: no friction or air drag; the launcher's push and the collision itself are taken as instant; elastic collisions are perfectly elastic; each glider is caught at the end of the track.
- Gliders A and B: total momentum is the same before and after
- Light gate: times the 100 mm card, v = 0.100 m ÷ t
- Launcher: a spring, ½kx² = ½mu²
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