An instructor balances a ruler with weights on his finger, as students look on.

In the demonstration pictured here, we illustrated the concepts of mean and variance by drawing a physics analogy with center of mass and moment of inertia. The prop is a wooden ruler with heavy boxes of paper clips secured by rubber bands. The mean corresponds to the balance point, located twice as close to the end with twice the mass. The variance corresponds to the energy needed to spin the ruler at a certain rate, and this energy is higher when the weights are farther out from the balance point.

Image courtesy of OCW.