Density is a measure of how much mass an object has per unit volume. Density is a compound measure because mass and volume can’t be measured in the same units. Objects denser than water sink, while ...

It is tempting to think that some materials are always heavier than other materials. For example, someone might say that metal is heavier than air. But it depends on how much of each material there is ...

A planet’s mass and volume are easy to determine. Because planets are nearly spheres, we can calculate volume from our knowledge of a planet’s radius, which we determine by measuring both the planet’s ...