Explore the fundamental concept of density in our latest post. Understand how mass and volume interplay, shaping the physical world around us. Dive into the core of density science!
“Which is heavier, a pound of feathers or a pound of lead?” This catch question is confusing, because heavy seems to have two meanings. Many people think that lead is heavier than feathers. But, of course, the question is really nonsense. A pound is a pound, whether it is a pound of feathers, lead, or anything else. In thinking about the pull of gravity on materials, scientists use a special word to avoid confusion. This word is density.
Materials not only have weight but also take up space. The amount of space that a material takes up is its volume. To understand density, you must think about weight and volume together. The density of any material is the weight of a certain volume of the material. If we are using the English system, we say that the material has a density of so many pounds per cubic foot. This means that each cubic foot of the material weighs a certain number of pounds. For example, the density of cork is 15.6 pounds per cubic foot, while the density of lead is 708 pounds per cubic foot. So lead is a much denser material than cork.
Density tells you what weight of a material will go into a certain volume. A box with 1 cubic foot of space in it will hold over 700 pounds of lead but only about 15 pounds of cork. The liquids as well as solids have different densities. A cubic foot of space will hold 42 pounds of gasoline or 849 pounds of mercury. The volume of liquids is often measured in gallons. So the density of a liquid can also be stated in pounds per gallon. For example, we can say that the density of water is 62.4 pounds per cubic foot or 8.34 pounds per gallon.
If you understand the meaning of density, you will not be confused by the catch question about lead and feathers. Your answer will be “Lead is denser, not heavier, than feathers.” Nor will you be fooled if someone asks, “Which is heavier, a pound of cheese with holes in it or a pound of cheese without holes in it?” You know that gravity pulls down on each of them with the same amount of force. So they both have the same weight but different densities.