Wednesday, November 17, 2010

First Law of Thermodynamics: Heating Sand by Shaking It

The first law of thermodynamics says that the total amount of energy in a closed system remains constant. There are many different forms of energy, and energy can shift from one form to another. So the total amount of energy in a closed system is the sum of all the different forms of energy added together.

To test this principle, we measured the temperature of sand in a Styrofoam cup.This experiment was suggested by Professor Robert Hazen in his video course The Joy of Science. In his video, he used a jar of sand. However, we decided to use insulated cups so we didn't have to open it to measure the heat. We first measured the sand's temperature, then we sealed the cup, shook it for about five minutes, and measured the sand again. The sand's temperature actually changed from 65 degrees Fahrenheit to 68 in just the five or so minutes we shook it.


2 disposable insulated cups (we used Styrofoam)
masking tape
and a food thermometer (the kind with a sharp metal probe.)

  1. Pour the sand into one of the cups until it is about three-quarters full. 
  2. Measure the temperature of the sand.
  3. Place the empty cup on top of the cup with the sand on it. Tape them together.
  4. Shake for five minutes.
  5. Poke the thermometer's probe though the top of one of the cups. Measure the temperature again. You should see the temperature go up a few degrees.
What Happened:

Shaking the sand is a form of kinetic energy. The friction of the sand particles rubbing against each other converts the kinetic energy to heat energy. Some of the kinetic energy also converts into the energy of sound waves, which you can hear while you shake the sand.

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