The amount of space between molecules or particles of any substance is what determines its density. Lead is more dense than aluminum which is more dense than wood which is more dense than foam rubber which is more dense than styrofoam. For this activity, we will compare not the depth, but the volume of the snow or water. Snow, on the other hand, is mostly air. As you can see, the density of snow is related to the measure of the water in snow.
Examples are especially helpful.
Allow the students to hold a brick and a block of wood or foam rubber the same size. Use an illustration to show something that is loosely filled with particles versus something that is tightly filled with particles. A fun activity is to have the children stand together in an area and give them instructions to space apart or bunch together to show the realities of high and low density. Ask the children how much water they use at home. Make a list on the board of all the things we use water for.