10. Archimedes Principle

A very simple demonstration is to attach a one kilogram mass to a spring scale and lower the mass into an aquarium of water. The weight under water is considerably less than the weight in air.

We have a much more elaborate apparatus with two large produce-type grocery scales, one over the other. The lower one holds a pan of water, and the upper one weighs a mass in air or in the water. You can measure the dimensions of the mass, compute the volume it displaces, weigh it in air and in water, and note how the weight of the pan of water changes when the mass is lowered into it.