This activity allows you to investigate how heat transfers through a crystal.

A crystal is held in place by van der Waals forces. When the crystal is heated, the heat propagates through the crystal.

How fast does heat propagate through a crystal?

1. This model starts with a crystal consisting of about 300 identical atoms that are held in place by van der Waals forces. Click on “K. E. Shading” that shades each atom according to its kinetic energy. Heat propagation is easier to see with “K. E. Shading” on.
2. Increase the average kinetic energy of the atoms by clicking the red and blue arrows on the “thermometer”. If you heat it too much, you will melt the crystal. You can always start over using the reset button.

3. Use the heating tool (the one with a sun and plus sign) to heat part of the crystal. Try clicking five times in one place to heat just one part of the crystal.
4. Run the model and watch what happens to the temperature of the crystal.

5. At any time, you can stop the model and select “Analysis>Grid>Temperature Distribution.” When you then run the model, you see the temperature profile of the crystal. Turn this off by selecting “Analysis>Grid>No Grid.”
6. The model is very slow—there are lots of calculations. To see it faster, run the model for about 200 cycles, stop it, pull the slider back to zero, and run again. Just for fun, run the model in reverse, using the left-arrow key.

1. When you run the model fast with KE shading, you see something streaming away from the hot part. What is this?
2. What causes it?
3. How long does it take to reach equilibrium?

What causes heat to propagate? How fast does it propagate?

What happens at the atomic level when a hot object is placed in contact with a cold one? Here, the green atoms start hot and the blue ones start cold. The graph at right plots the temperature of the green and blue atoms separately. What do you think you will observe on the graph?

This model starts with about 50 pulses of heat in the upper atoms and the lower atoms almost at rest. The blue atoms are twice as massive as the green ones.