Density: Definition, Formula & Practice Problems

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  • 0:04 What Is Density?
  • 1:12 Calculating Density
  • 2:29 Lesson Summary
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Lesson Transcript
Instructor: Richard Cardenas

Richard Cardenas has taught Physics for 15 years. He has a Ph.D. in Physics with a focus on Biological Physics.

In this lesson, you'll learn about density, the way in which density can be calculated from mass and volume, and that density of substances are constant. You'll get to calculate densities of various materials in different situations.

What Is Density?

Let's say we have three identical cubes. Each side of the cube has a 1.0-centimeter length. One cube is made out of lead, the second cube is made out of aluminum, and the third cube is made out of wood. If I asked you which cube would be the most dense of the three cubes, you will most likely say the one made out of lead. Simple enough. But what, just exactly, is density?

Density is defined as the ratio between mass and volume or mass per unit volume. It is a measure of how much stuff an object has in a unit volume (cubic meter or cubic centimeter). Mass is a measure of how much stuff an object contains, and volume is the measure of how much space an object occupies in three-dimensional space. This figure shows a dense object versus a less dense object:

Dense versus Less Dense

As you can see in the figure, the dense object (A) has more stuff than the less dense object (B). Both objects are shown to occupy the same space.

Calculating Density

So, how do we find the density of an object? As you saw, you need two pieces of information in order to calculate density: mass (in grams or kilograms), and volume (in cubic centimeter or cubic meter). The formula for density is:


Going back to the three cubes in the beginning of the lesson, let us calculate the densities of the three objects. Let's say we have 11.3 grams of lead, 2.7 grams of aluminum, and 0.67 grams of wood (pinewood). The densities are calculated as mass per unit volume (1 cubic centimeter).

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