Your brain harnesses a hidden skill that you didn’t know you had.
We can tell the difference between hot and cold water purely through sound.
People hear hot and cold drinks poured so often that they subconsciously learn the difference between the two.
In a new video, science presenter Steve Mould puts this theory to the test with a hot and cold water quiz, revealing that it is surprisingly easy to pick between the two.
he first pour in the video is cold, while the second pour is hot.
The two sound different because hot and cold water have a different viscosity or ‘thickness’.
‘The viscosity of water goes down when you heat it,’ Mr Mould explains in the video.
‘This is easier to see with a liquid like honey – warm honey is more runny than cold honey.
‘With water this is less visually apparent, but when you pour water, the way it splashes into a cup is affected by the viscosity.’
The slight changes in viscosity between hot and cold water change the sound of the splashes when poured.
It is these subtle changes that our brains learn over time.
The two sound different because hot and cold water have a different viscosity or ‘thickness’. Cold water has a higher viscosity, meaning its molecules are less energised, and so they make a different sound when they ‘splash’ at the bottom of a mug or shower
Heat changes the viscosity of liquids because it energises the molecules.
In cold water, the molecules carry less energy and are less ‘excited’, meaning it is more viscous.
This means that the water molecules move more slowly and are more likely to ‘stick’ together.
Cold water’s higher viscosity also causes it to bubble less when poured.
This creates a lower frequency sound, the Naked Scientist reports.
Hot water on the other hand produces a higher pitched sound when poured because the energised molecules are moving around more rapidly.
It is these small differences in sound that our brains have learned to distinguish, and this is why we can pick out hot and cold water just with our ears.