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What Is Density? - Explanation & Examples

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  • 0:00 What Is Density?
  • 1:20 Examples
  • 2:01 Calculation
  • 3:23 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain what density is, give examples of high and low density, and calculate density using an equation. A short quiz will follow.

What is Density?

Density is a measure of how compact the mass in a substance or object is. The density of an object or substance can be calculated from this equation: density in kilograms per meter cubed is equal to mass in kilograms, divided by volume in meters cubed. Or in other words, density is mass spread out over a volume. Or in other, other words, it's the number of kilograms that 1 meter cubed of the substance weights. If each meter cubed weighs more, the substance is more dense.

As we'll discuss in other lessons, density is super important because it relates to whether things rise or sink. Less dense materials tend to rise above more dense materials, particularly in the case of liquids and gases. So understanding density has major implications for the motions of materials and gases in the atmosphere and objects floating (or sinking) in water. Density is the reason some objects sink and other objects float. And it's the reason that some clouds are high in the sky, while others are low down.

Density means that if you take two cubes of the same size made out of different materials and weigh them, they usually won't weigh the same. It also means that a huge cube of Styrofoam can weigh the same as a tiny cube of lead.

Examples

Examples of dense materials include iron, lead, or platinum. Many kinds of metal and rock are highly dense. Dense materials are more likely to 'feel' heavy or hard. Although a sparse material (sparse is the opposite of dense) can feel heavy if it's really big. Examples of sparse materials would be Styrofoam, glass, soft woods like bamboo, or light metals like aluminum.

In general, gases are less dense than liquids and liquids are less dense than solids. This is because solids have densely-packed particles, whereas liquids are materials where particles can slide around one another, and gases have particles free to move all over the place.

Calculation

Let's go through an example of how to use the density equation, which you may recall is density in kilograms per meter cubed is equal to mass in kilograms, divided by volume in meters cubed.

Let's say you have a cube of an unknown solid. You measure one of the sides of the cube and it is 0.1 meters long. You weigh the cube and it is 7.8 kilograms. Using this density data table, identify the solid.

Material Density (103 kg/m3)
Aluminum 2.7
Gold 19.3
Lead 11.4
Iron 7.8
Rubber 1.5
Window glass 2.579
Bamboo 0.35
Oak 0.77

Well, first of all, we should write down what we know. We know that the length L of a side is 0.1 meters and we know that the mass m is 7.8 kilograms. Looking at our equation, to figure out the density, we'll need both the mass and the volume. So we first need to figure out the volume.

The volume of a cube is length times width times height. And the sides of a cube are all the same length. So the volume will be 0.1 times 0.1 times 0.1, which is 0.001 meters cubed.

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