What it shows:
Potential energy curve with potential barrier illustrates electron-atom, atom-atom or ion-ion interactions.
How it works:
This is a one dimensional potential well model with a potential hill that can be used to represent several scenarios. The wooden model is made of a sandwich of three strips of plywood (1/4"-1/2"-1/4") forming the cross section as shown in figure 1. A 1" ball bearing fits snugly enough into the groove that it won't fly out when it hits the barrier.
figure 1. The roller coaster potential shape and its cross-section.
figure 2. Photo of apparatus.
Here we list three things it could be used to show (we can't remember what it was originally built for!):
1. Activation energy. The well shows the optimum separation for a stable molecule, but when the atoms approach, the interaction is initially repulsive. An additional energy - the activation energy - is needed to overcome this barrier. Examples would be the breaking of O2 and H2 bonds to allow the formation of water, or the ionization of sodium to allow the formation of an ionic bond with chlorine. The ball bearing represents an ion or atom.
2. The potential for an electron approaching a multi-electron atom. Here the hill is the coulomb repulsion of the electron cloud.
3. A generic potential barrier. Depending upon where you release the ball bearing, it may or may not escape over the hill. Of course, you need to release it from a height greater than the hill height. This is classical barrier penetration.
Setting it up:
Stands on a lecture bench (wooden feet, not shown, keep it from falling over). You may want something to trap the ball as it shoots off the end of the well.
Not used very much these days, but a good shape for show-and-tell even without the ball bearing.