Moving Water Molecules

(Chemistry for ages 5+)

Did you know that liquids are actually moving all the time, even if they look still? Water, for example, is made up of tiny molecules of 2 hydrogen atoms and 1 oxygen atom. These molecules are constantly moving around and bouncing off of each other even if you can’t see it happening. Like the video above shows, one cool way to see these tiny movements is with some food coloring. Here’s how you do it:



2 clear cups

Blue food coloring

Red food coloring

Hot water

Cold water

Adult supervision (Adult Supervision at all times please)



  1. Fill one of your clear cups with cold water. This can be from the tap or water that has been in the refrigerator.
  2. Next, fill the other cup with hot water, either from the tap or warmed on the stovetop or in a microwave. Boiling water is not recommended.
  3. Add 1-3 drops of blue food coloring to the cold water, and 1-3 drops of red food coloring to the hot water. If you do not have red and blue, use whichever colors you have on hand. Try to add them at the same time, but if that is not possible, add food coloring to the cold water first.
  4. Do NOT stir the food coloring in. Watch as the color mixes in naturally. What is different about the cold and hot water?



When water is heated, individual molecules have more energy and move around faster than they do in cold water. This faster movement allows the food coloring in the hot water to mix in much faster, while the food coloring in the cold water takes a while to fully mix in because those molecules are less energetic and moving slower.