# Particle Theory and Density Quiz

Do you know how to calculate density?

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## What is Particle Theory (Kinetic Theory)?

Particle Theory is a set of assumptions about the microscopic (small scale) that we use to explain the macroscopic (large scale) phenomena that we experience. The assumptions allow us to develop explanations that are logically consistent with each other and are easy to understand.

These assumptions are that all matter is made of very small, hard, inelastic, spherical particles. These particles interact in predictable ways which allow us to develop models of the states of matter; solids, liquids and gases.

By using Particle Theory (also known as Kinetic Theory), we are able to not only understand the characteristics of different states of matter, but also the phase changes and why they happen when they do.

Another quite important benefit of using the Particle Theory of Matter to explain states of matter is that we are able to teach others and explain these concepts in simple language, making the knowledge accessible to most people.

The Particle Model of Atoms also allows us to talk about related topics and measures such as density and pressure, in the context of states of matter and energy.

Density is simply the ratio of matter to volume, with a substance that has more matter per unit volume being denser than a substance with less matter per unit volume.

We use the following equation to calculate density:

density = mass/volume

This equation can also be rearranged to get mass or volume given the other two measurements.

Given the equation for density, it is easy to understand that gases are the least dense of the three states of matter. Liquids are between gases and solids in terms of density, whilst solids have the highest density of the three states.

Particles in all three states of matter are constantly moving, since all objects that are hotter than absolute zero or 0 Kelvin have kinetic energy, meaning movement energy which is actually the same as temperature. Gases just have a greater amount of this energy than liquids or solids.

If you would like to find out more, check out our States of Matter Quiz and Explainer.