Assemble a number of liquids of different, but known, densities.
Arrange them in ascending order of density.
One-by-one, place your object in the different liquids
If your object
Is denser than the liquid, it will sink
Is less dense than the liquid, it will float
Has the same density as the liquid, it will submerge, but it will neither sink nor float
If you have a steady hand you can create a liquid density tower, as in the diagram below. You can see that the ping-pong ball sits on top of the lamp oil, but the cherry tomato is suspended in the dish soap.
