Simple Science Experiment: Molecular Motion with Heat Changes - MetroFamily Magazine
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Simple Science Experiment: Molecular Motion with Heat Changes

by Steve Davala

Reading Time: 2 minutes 

When you look at a glass of water that has been sitting there awhile, it sure looks like nothing is moving. But maybe you’ve heard of something called “molecules,” and you know that things are always moving, even if it is on a really small level. A molecule is the smallest part of a substance that still has its properties. For example, the smallest piece of water is a molecule. How big is that? Well, in a drop of water there are a lot of molecules. About 1,000,000,000,000,000,000,000 molecules in there. That’s a lot.

How can we test to see if things are moving on a micro level? Water is clear, right? And if we can test it, can we change the rate of motion at all? The following simple experiment will test to see if molecules are in motion even though they look like they are standing still, and also to see how heat changes might change that motion.


Three tall clear drinking glasses, water to fill each, ice, a pan to heat water, and food coloring.


  • Fill three clear drinking glasses halfway with water.
  • Put three or four ice cubes in one glass.
  • Heat one glassful of water on the stove, close to boiling. Pour the water back in the glass.
  • While letting that sit, remove the ice cubes from the glass.
  • Let the three glasses sit so they appear still (just a few minutes).
  • You will be putting a drop of food coloring in each glass to track motion.
  • Take a guess as to what will happen in each glass. A hypothesis requires you to think why it will happen that way.
  • Put a drop of a single color coloring into each water glass and observe!


You will see how quickly the food coloring in the hot water moves, and how slowly the drop moves in the cold water. The middle temperature water is right in the middle. Did you see how the color twists and turns in the hot water, as soon as you put it in the glass? That motion reflects the molecular motion in there. All things move, even though we can’t see them. The colors just allow us to track the motion.

But why does it move so quickly in the warm water, as opposed to the cold one? “Heat” is a measure of how much energy is in something, or the amount of collisions each molecule has with one another. That’s right; the molecules are hitting each other and causing the heat. The hotter it is, the faster the molecules are moving and the more they are hitting each other. On the flip of that, the colder the material, the slower the molecules are moving.

Experiment further:

With all science, things don’t start to get too interesting until you start throwing your own ideas into the mix. What can you change about this experiment to further your learning? We tried water, what other liquid can you test? Earlier I mentioned to use the same food coloring… why? Do different colors move at different speeds? Remember, be safe, but ask good questions and test your ideas. 

I hope you enjoyed this simple experiment.  If you have more questions about this, or need tips about science fair ideas around this topic (or others), contact the author.

Steve Davala is a middle school science teacher who likes to write and work with Photoshop. He’s got two kids of his own and subjects them to these science activities as guinea pigs.                                                                            

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