Linear Momentum and Collisions
Elastic and inelastic collisions - Dynamics carts of collide and spring apart
Use the dynamics track and carts with springs attached. You can show qualitative relationship. Have them "spring" apart or give them velocity together and have them bounce back, or use the Velcro side together to have an inelastic collision, or have one stationary and slam the other cart into it. The carts can be the same or different mass with the weights added.