While exploring volume by pouring colored water into our clear plastic forms Aidan discovered today that the forms could be used together in interesting ways.
He inserted a pyramid into a cube full of colored water. When he aligned the base of the pyramid with the open side of the cube he could turn the whole thing upside down and surprise! the water trapped between the pyramid and the cube does not run out.
You would think gravity would quickly pull the water down and out to the floor. It is very counterintuitive that it stays inside.
The pyramid can be lifted easily out of the cube when it is turned over.
A similar effect can be done with a cone and a cylinder, as Robert shows here.
And, oh. It's fun, too.