Oil and water are two liquids that are immiscible, meaning they will
not mix together. Liquids tend to be immiscible when the force of
attraction between the molecules of the same liquid is greater than the
force of attraction between the two different liquids.
Although this experiment uses the same volume of oil as water, the
two liquids have different masses and therefore, different densities.
Density is a measure of how much of a substance is contained in a
specific volume of liquid. A liquid that is less dense than water will
float on the water; a liquid that has a greater density will sink.