Did you know you can hear temperature?

Our bodies are full of surprises and can never cease to amaze you. Even our ears. In fact, we can hear the difference between hot and cold water!

What do you need?

• Kettle

• (Measuring) cup

• Tap water

• Two identical mugs or cups

• Test subject

• Blindfold (optional)

Be careful with the boiling water. If necessary, ask an adult for help.

Getting to work!

Step 1: Make sure your test subject does not see the experiment. Use a blindfold or ask the person to turn around during the experiment.

Step 2: Put a kettle on with about one cup of water in it.

Step 3: Fill the (measuring) cup with cold water. Water from the tap is fine, it doesn't have to be ice cold.

Step 4: Place two empty cups on the table, next to your test subject.

Step 5: Tell your test subject that you are going to pour water twice. Once hot water and once cold water, but don't tell in which order you will do this. What difference do you think you will hear between the two?

Step 6: Now pour both cups full. One with cold and one with hot water. Try to pour in the same, calm manner both times. Think about speed and height of pouring.

Step 7: Now ask your test subject which of the times was hot, and which was cold. Is it correct?!

What's happening?

About 90% of people will give the right answer.

Why though?

A difference in sound can indeed be heard. This is because hot and cold water have a different viscosity. Consider honey, for example. Cold honey is very viscous and flows very slowly. If you warm it up, it becomes less viscous. It flows more quickly.

What is less viscous than honey, but the same thing happens with water too. When you heat it up, it becomes even less viscous than it already was. You cannot see the difference, but you can hear it when you pour it out.

We can hear that difference because we are unconsciously 'trained' in that difference all our lives. After all, you very often hear someone pouring a cup of tea or coffee, or a glass of plain water.

Where else do you encounter that?

In some liquids, the viscosity changes when you apply pressure to it. Think about peanut butter. When you open the jar, the peanut butter is usually too viscous to spread. If you stir it for a while, the peanut butter will become less viscous.