When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren’t moving quite so fast. Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels. Your body has a variety of antennae to detect energy. Your eyes perceive certain frequencies of electromagnetic waves as light. Your ears perceive certain frequencies of longitudinal waves as sound. Your skin, mouth and tongue can perceive thermal energy as hot or cold. What a magnificent energy sensing instrument you are!

Let’s find out how to watch the hot and cold currents in water. Here’s what you need to do:

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  • two bottles of water
  • food coloring
  • bathtub or sink
  • index card or business card

You need:

Two empty bowls (or water bottles)
Food coloring
Hot water (Does not need to be boiling.)
Cold water

1. Put about the same amount of water into two bowls. One bowl should be filled with hot water from the tap. If you’re careful, you can put it in the microwave to heat it up but please don’t hurt yourself. The other bowl should have cold water in it. If you’re using water bottles, pour the hot and cold water into each bottle.

2. Let both bowls sit for a little bit (a minute or so) so that the water can come to rest.

3. Put food coloring in both bowls (or bottles) and watch carefully.

The food coloring should have spread around faster in the hot water bowl than in the cold water bowl. Can you see why? Remember that both bowls are filled with millions and millions of molecules. The food coloring is also bunches of molecules. Imagine that the molecules from the water and the molecules from the food coloring are crashing into one another like the beans on the plate. If one bowl has a higher temperature than the other, does one bowl have faster moving molecules? Yes, the higher temperature means a higher thermal energy. So the bowl with the warmer water has faster moving molecules which crash more and harder with the food coloring molecules, spreading them faster around the bowl.

If you’re using a bottle, you can do an extra step: For bottles, place a business card over the cold bottle and invert the cold bottle over the hot. Remove card.


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