# What is Density?

In order to help us understand density, let's take a look at two classrooms. Classroom one could be described as having a dense population of students. Compare this to classroom two, which would be considered a low or less dense population of students.

So what is density?  Density is a measure of the mass of an object per unit volume. It is a measure of how compact the atoms inside of an object is. Density is just a ratio of mass to volume.

What determines the mass of an object?
Everything is made up of matter, stars, mount everest, and you.

Matter is made up of very small particles called atoms which give objects their mass. Some objects like gold, have atoms that are compacted very tightly. This creates a greater density than other objects like helium which have atoms that are less compact and further apart and therefore have a smaller density. This is why a balloon filled with helium will float.

You can calculate the density of an object by finding the
mass of the object and then divide this by the volume of the same object. If you take a look at this cylinder it's filled with different liquids.

The most dense liquids will be on the bottom and the least dense objects will settle on top. This is a rule of density, objects with less density will always settle on top of objects with a greater density.  An easy way to remember the formula for density is to just use " I heart density"
The heart creates an m and a v so you have mass divided by volume equals density.

What are some common units used to measure density?
Common units for density include,

gram per milliliter  g/mL

gram per centimeter cubed g/cm^3

gram per liter g/L

kilogram per liter kg/L

kilogram per meter cubed  kg/cm^3

What is the SI unit for density?
kilograms per cubic metre (kg/m^3)

What is the symbol for density?
The Greek symbol rho (ρ).