Sink or float?
Archimede's principle: an object immersed in fluid is buoyed up by a force equal to the weight of the fluid displaced by the object.
You can choose between water or alcohol for the testing liquid. Materials that are less dense than the testing liquid will float.
The density of (fresh) water is 1.0 grams per cubic centimeter (g/cm3) and alcohol is about 0.8 g/cm3.
If you consider the following densities:
- ice is 0.9 g/cm3
- walnut is 0.5 g/cm3
- stone is 2 g/cm3
then you will be able to explain why the ice cube floats in water and sink in alcohol.
Safety precaution: alcohol is a flammable liquid; keep away from all flames.