Tennesee Science Standard: GLE 0107.9.1- Classify solids according to their size, shape, color, texture, hardness, ability to change shape, magnetic attraction, whether they sink or float, and use.
You can teach your students how things sink and float. You can have a class discussion about how you change the shape of an object it changes the mass and density.
Materials needed: Modeling clay, marbles or stones, bowl, and water
Step One: Drop marbles into the water. They quickly sink to the bottom.
Step two: Roll the clay into a ball and place it into the water. It quickly sinks also.

Step three: Shape the clay to make a boat.

Step four: Place the clay boat into the water. The clay floats!! The boat is bigger than the ball and diplaces more water.

Step five: Add the marbles inside the boat.

Step six: The boat and marbles displace more water, but still floats!!

We made objects sink, then float.
How did we do that?
Whether something sinks or floats has nothing to do with how much an object weighs.We did change how much the object weighs; we changed the shape of the object. An object floats or sinks based upon how much water is diplaced, or "pushed aside." the boat made out of clay was bigger than the ball of clay and displaced, or pushed aside, more water causing it to float. The marbles couldn't float because they were small and could't push enough water out of the way to equal the same weight. So, it is important to remember that anything that floats weighs the same as the water pushed out of the way. This very same principle is used when building ships. I think this would be a great experiment to use in the classroom. I think everyone wants to know just how a boat can float when it is so big. This experiment could be used to teach about density, water displacement, and volume. Students could also have fun with the experiment by seeing who could make their boat hold the most marbles.
DENSITY is a physical property of matter, as each element and compound has a unique density associated with it. Density defined in a qualitative manner as the measure of the relative "heaviness" of objects with a constant volume. When the clay was in the ball the density was smaller. When the clay was in the shape of the boat the denisty was larger.