Fun and easy science experiments for kids and adults.

Water bowls

Put your hands in hot and cold water and be fooled. Your hands can not agree on the result in this experiment about the brain.

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Video

Materials

3 bowls (big enough to put your hands in)
Water

Step 1

Pour cold water into one bowl and hot water into another bowl. The coldest and warmest from the tap is enough. Finally, pour room temperature water into a third bowl.

Step 2

Place the three bowls in front of you.

Step 3

Put one hand in the hot water and the other hand in the cold water. Hold them there for 30 seconds.

Step 4

Then place both hands in the room temperature water. Do your hands feel the same?

Short explanation

The human sense of temperature is sensitive to change. For example, when your hand is moved from cold to room temperature water, your body signals that the water is very hot - even if it's not.

Long explanation

Temperature is a measure of how fast a substance's constituent particles move. In hot water, for example, the water molecules move around quickly, while in cold water they are slower.

The fascinating thing about temperature is that humans have the ability to register it. Somehow the body can "measure" how much the particles in a substance move. Exactly how this happens is still not fully understood, but it does include several types of specialized nerve cells that send signals to the brain when they detect something that is hot or cold.

The sense of temperature is partly relative. This means that some nerve cells only send signals to the brain when the temperature changes. So if the body cools down to a certain temperature, these nerve cells will only send signals during the actual temperature change, but when the body has stabilized at a certain temperature, they stop sending signals. Therefore, when your warm hand was placed in the room temperature water, these change-sensitive nerve cells sent a message to the brain that "now it got cold" - even if the water was not really cold. The same thing happened in your second hand. When you placed your cold hand in the room temperature water, nerve cells sent a message to the brain that "now it got hot" - even if the water was not really very hot.

It is easy to understand why humans have an evolutionary advantage in sensing temperature changes in this exaggerated way. We need to react quickly to avoid getting burned or getting cooled.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

What is the shortest time you have to hold your hands in the hot and cold water respectively to achieve this effect?
How does it feel if you hold your hands for a very long time in the hot and cold water, before dipping them in the room temperature water?
How fast can you register the temperature change?
What is the smallest temperature difference you can have between the water in the bowls, and still achieve this effect?
Does it work if you only dip one finger in each bowl?