One way to celebrate Grav-Mass is to decorate a tree with apples and other fruits. Glue them or attach them, but not too well! The idea is that occasionally a fruit should fall. Put them on the tree no more than 2 feet up, so that they won't get damaged or hurt anybody when they fall. Investigating and perfecting the methods for doing this is a great way to expose a child to the process of scientifically studying the behavior of the physical world.
by Richard Stallman