Experiment to demonstrate a property (density) of materials
Density is a measure of how heavy an object is for a given size i.e., mass of material per unit volume.
If an object is more dense than water it will sink when placed in water, and if it is less dense than water it will float. My experiment demonstrates this property of materials as we can see that lighter objects float and heavier or denser objects sink.
Practical application of this property can be seen when Hollow things often float as air is less dense than water.
This is partly the reason why huge and heavy ships float. Another thing is to consider the shape of an object. Generally, the more of the outside of an object that is touching the water, the more buoyant it is.
This activity demonstrates how reducing the density of a heavy object allows it to float as in case of vessels and watercrafts.