Conservation of Momentum Demos

There is a 20 lb bag of rice. Two students can sit on the carts facing each other. They then toss the bag of rice back and forth. They should try not to break the bag and get rice all over, it not a wedding, besides birds explode when they eat it. They should toss with some speed.

You can then discuss conservation of momentum both for toss and catch. Beware of discussing fundamental interactions, as someone will ask how you get an attractive force.

Another good one discovered by Darien, you can give empty cart a constant v. Then drop stationary sand (rice) bag onto cart, which slows down nicely.