The y axis of the graph shows the probablity that the speed of a molecule in a gas lies between x metres per second and and x + 1 metres per second. The curve shown corresponds to a temperature of about 80 K

- The red graph shows the curve for Helium gas
- The blue graph shows the curve for Argon.

Notice that:

- The area under each graph is the same.
- The area under each graph is equal to 1.
- At any chosen temperature, helium atoms tend to move faster than argon atoms.
- There is a wide spread of molecular speeds in a gas.
- Even at low temperatures, some molecules move very fast: many hundreds of metres per second

The quicktime animation below shows the effect on the MB curve of heating from around 80 K to 500 K.

The graphs above are based on the formula shown below.

k is the value of the Boltzmann constant, m is the mass of a helium atom and n is the mass of an argon atom

This file was created by Graphing Calculator 3.0.

Visit Pacific Tech to download the helper application to view and edit these equations live.