If you've ever mixed water and oil together,you've probably noticed that the oil rises to the top and the water stays at the bottom-- no matter how much you try to shake them. This is because oil is less dense than water, making it float to the top. The molecules in oil are larger than those in water, so they don't pack as tightly together as they do in water. In a mixture of oil and vinegar, the oil floats on the vinegar/water mixture, while the solids sink to the bottom. So, if one material floats over another, the material on top is less dense.
Let me know if this helps! :)
