Introduction

Three magnets on a pencil can be uased to model one of the oscillations of atoms in a carbon dioxide molecule that absorbs infrared radiation.

Material

Three donut magnets with center holes larger than the diameter of a pencil.
A new unsharpened pencil

To Do and Notice.

Place the three magnets on the pencil so that the two at each end repel the one in the midlle.

Hold two magnets in place at the ends of the pencil, (or tape them or glue them in place.)

The third magnet should be near the center.

Shake the pencil back and forth along its length. Watch the center magnet shuttle back and forth between the end magnets.

When you move the pencil back and forth at too high a frequency or too low a frequency the middle magnet does not move more than the distance you move your hands, however when you move the pencil back and forth at the resonant frequency the center magnet moves back and forth much further than you move your hands due to resonance.

What's Going On ?

In a molecule of CO2 the three atoms are in a row with oxygen atoms at the ends and the carbon in the middle. Covalent bonds connect the molecules keeping them together and apart. if the central carbon atom is shoved toward one end it will bounce off the end and oscillate back and forth just like the central magnet in this model.