How to use: Two carts sit on one track, facing each other.
The left cart sets off right at the speed you give it and the right
cart sets off left at its own speed, so you can send one into a
parked cart, meet one head on, or watch one overtake the other. Set both
speeds to zero and nothing will happen at all. Left cart and
Right cart are their masses. Bounciness decides how much of
the closing speed comes back: at 1.00 the impact is
perfectly springy and the carts bounce apart, at 0 they lock
together and stay locked. Press Launch.
Momentum is mass times velocity, added up across both carts. It comes out
of a collision exactly as it went in — that is Newton's third law, and the
arrows on each cart during the impact are the two halves of it: the same
size, opposite ways. Kinetic energy is the other matter. Only a perfectly
bouncy collision gives all of it back; a squashed one turns the missing
share into heat, sound and dented metal.
The push quoted is the average force over the impact, worked out from each
cart's change in momentum spread over a contact time of 0.02 s.
Notice: momentum is always handed over, but energy is only handed over
when the carts bounce. A soft collision keeps every last bit of momentum and
throws away energy — which is why a brick dropped from a height hurts more
than the same brick stopping gently against your hands, even though in both
cases the momentum going into your hands is the same.