H2 Physics Collision Practical: Cart Velocities, Momentum and Safety

A collision happens quickly. To investigate it, measure what both carts are doing just before contact and just after they separate or move together. Watching one cart alone cannot establish whether the two-cart system conserves momentum.

This is a reading guide for a supervised, low-speed cart investigation on a supported track. It does not confirm the apparatus used in an Eclat lesson. Follow the trainer's equipment-specific briefing, including where the carts must stop. Read Lab safety starts before the experiment for the wider preparation and supervision principles.

What the investigation tests

The 2026 H2 Physics syllabus, 9478, covers one-dimensional elastic and inelastic interactions on page 15. A cart experiment illustrates this theory; the syllabus reference does not make this particular apparatus a compulsory practical.

Choose a positive direction along the track. Momentum uses signed velocity: a cart moving in the opposite direction has negative velocity. Kinetic energy uses speed squared, so it has no direction sign.

Compare the total momentum of both carts before and after contact. Conservation is a useful approximation when external impulse on that system is negligible over the measured interval. Track friction, a sloping track or contact with an end stop can change the comparison.