September 27, 2025

What Is Density

Q: Why do some objects float and others sink?

An object floats if it is less dense than the fluid it is placed in. An object sinks if it is denser than the fluid. This is why a ship made of steel (very dense) can float: its hollow shape displaces a large volume of water, making its overall average density less than water's.

Q: Does temperature affect density?

Yes. For most substances, as temperature increases, the volume also increases, which causes the density to decrease. A common exception is water, which is most dense at 4°C (39°F).

Learn the definition of density, how it's calculated using the mass and volume formula (ρ = m/V), and understand why some objects float while others sink.

Have More Questions →

Defining Density

Density is a fundamental physical property of matter that measures how much mass is contained within a specific volume. In simple terms, it describes how tightly packed the 'stuff' in an object is. An object with a high density has a lot of mass concentrated in a small space.

Density Formula and Example

The formula to calculate density is ρ = m/V, where ρ (the Greek letter rho) is density, m is mass, and V is volume. For example, if a block of wood has a mass of 80 grams and a volume of 100 cubic centimeters (cm³), its density is 0.8 g/cm³. Because this is less than the density of water (1 g/cm³), the block of wood will float.

Frequently Asked Questions

Why do some objects float and others sink?

Does temperature affect density?