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Can you compress water?

Question

Can you compress water? If you had an airtight box, would it be possible to compress the H2O?
Tom, Dorking

Answer

** Definitive **
Name: Professor Hal. Brighton
Qualification: Mystery Hour’s Most Capped Correspondent
Answer: The strict answer is yes, but the general answer is no. It’s a tiny bit compressible, but it’s so miniscule that, like most liquids, you can regard it as a non-compressible, which is why hydraulic fluids work so well. However, as a side-point, water’s density is interesting. It contracts as it gets colder – like most things. But under 4 degrees, it actually starts expanding again, which is why ice is less dense than water. Hence, ice floats, which you wouldn’t expect. And that explains why you need anti-freeze in your engine. Without it, the water will freeze, expand and crack your engine block.

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