Teaching Physics with the Physics Suite

Edward F. Redish

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Scales in a gas

The actual diameter of an atom is about 1 Angstrom (10-10 m). In order to develop some intuition for the molecular scale of a gas, assume that you are considering a liter of air (mostly N2 and O2) at room temperature and a pressure of 105 Pa.

  1. Calculate the number of molecules in the sample of gas.
  2. Estimate the average spacing between the molecules.
  3. Estimate the average speed of a molecule using the Maxwell-Boltzmann distribution.
  4. Suppose that the gas were rescaled upwards so that each atom was the size of a tennis ball (but we don't change the time scale). What would be the average spacing between molecules and the average speed of the molecules in miles/hour?

Page last modified October 30, 2002: M15