Let’s say you have a brick and a piece of Styrofoam that are exactly the same size. Which one weighs more? Chances are, you said the brick weighs more but do you know why? It’s all about density.
- The density of an object is determined by two things: the mass of the molecules in the object, and how tightly packed the atoms are together.
- A brick has high density because it is made from molecules that have a lot of mass. The atoms are packed closely together.
- Styrofoam is low density. The molecules in Styrofoam don’t have a lot of mass. The atoms are loosely packed with lots of holes and air between them.
- Density and buoyancy are interconnected. Which object is likely to float, the brick or the Styrofoam? You’re right if you guessed the Styrofoam. Low density objects will float on a material that is higher in density (such as water).
- Think of other materials that are low or high density. Wood, cork, and sponges are all low-density materials. So are most natural materials, such as pumpkins, peppers, or pine cones. Cement, metal, and glass are high-density materials.
- Density: refers to the mass of the molecules in a material and how tightly the atoms in the material are packed together
- Low-density: materials containing molecules with less mass and atoms that are loosely packed
- High-density: materials containing molecules with more mass and atoms that are tightly packed
Question and Answer
Question: Why does density matter?
Answer: Understanding density can help you predict whether or not something will float. This matters a lot of you want to float down a creek and you’re choosing a flotation device.
Did you know that some liquids are denser than others? Some liquids can float on top of others. Head over to PBS to learn more.