Combine one red and yellow drop. Combine one blue and yellow drop. Combine one red, yellow, blue drop. Give each student one drop of soapy water. Repeat the steps above for small groups, as necessary.
Place objects in a tub of water of varying depths.
Look through the water at the objects. Add soap to the water. Water has cohesion - the molecules hold together. We can break a water bubble apart and put it back together. The bubble stays together as we move it.