Why is water heavy?

[Rupert_Baehr]

when it's not at atmospheric pressure

 

Why would that make a difference? Water is a liquid. It is not compressible.

[Grandad.Malky]

when it's not at atmospheric pressure

 

Would there be an appreciable difference to the weight of 1lte of water on the top of Everest assuming it hadn’t frozen obviously.

 

Edit

 

litre of fresh water would weigh about 999.972g

 

Thanks for the answer I will take that as a no then.

[Lockjaw]

Water is a liquid. It is not compressible.

 

Always?

 

Do you think it is possible to have a litre of water vapour which has a mass of 1 kg?

[Lockjaw]

At the top of mount Everest, a litre of fresh pure water [at 4 °C] would weigh about 999.972g

 

... edited for correctness.

[Rupert_Baehr]

Water vapour(usually referred to and encountered as steam) is a gas. Water is a liquid. Ice is a solid.

 

As you reduce the atmospheric pressure above water, so the boiling point is lowered. Conversely, if you increase the pressure (as in a pressure cooker) the boiling point rises.

 

If you boil water (and convert it into its gaseous form, steam) and if you then compress the gas considerably whilst increasing the temperature it would (theoretically ) be possible to produce one litre of steam (under very high pressure and at very high temperature) with a mass of 1Kg.

 

That litre of steam which had a mass of 1kg would be commpressible - but it would be steam, not water.

 

Liquids are not compressible (See Pascal's Principle)

 

When you compress a gas, you reduce the space between the molecules. Not too difficult.

 

To compress a liquid, you would have to reduce the space between the molecules. You would need considerably more force. - If you've got enough force, you could reduce the volume very slightly.

 

To compress a solid you would have to reduce the space between the molecules. You would need a very large force indeed. - But it can be done. - That's how you can make a sub-critical mass of Plutonium into a critical mass.

 

It's generally accepted that solids and liquids are not compressible because the forces required are extremely large.

[HeadingNorth]

The theoretical maximum by which water can be compressed is still only about 5 per cent. At the bottom of the Marianas trench, the pressure is enough to reduce 1kg of water to about 0.98 litres, but no more.

 

Temperature and distance from the centre of the Earth are the other two variables. None of them make such a huge difference as to be worth worrying about by the layman. If you say "a litre of water weighs a kilogramme" you're right enough for practical purposes.

[Lockjaw]

If you boil water (and convert it into its gaseous form, steam) and if you then compress the gas considerably whilst increasing the temperature it would (theoretically ) be possible to produce one litre of steam (under very high pressure and at very high temperature) with a mass of 1Kg.

.

 

That's a yes, then? in that case you've answered your own one from post 31 and vindicated Strix.

 

Thanks for the, mostly, GCSE level physics lesson, Rupert. I do have one question though.

 

If, as you suggest (in order, some might suspect, to try to prevent your previous posts looking factually incorrect) "water" is the liquid form, "ice" is the solid form and "steam" is the gaseous form then what is the general name of the substance which covers all three states? I think you'll find it's dihydrogen oxide, more commonly known as, um, water.

[Lucy-Lastic]

People do seem to have got a little confused by mass and weight on this thread. Mass (measured in kg) should not change wherever you go - a 1kg object will still have a mass of 1kg at the North Pole, South Pole , Equator or the moon for example. Whereas the weight (which is measured in Newtons) is affected by gravity.

[Guest sibon]

People do seem to have got a little confused by mass and weight on this thread. Mass (measured in kg) should not change wherever you go - a 1kg object will still have a mass of 1kg at the North Pole, South Pole , Equator or the moon for example. Whereas the weight (which is measured in Newtons) is affected by gravity.

 

jacksrake is always getting those two mixed up:)

[HeadingNorth]

People do seem to have got a little confused by mass and weight on this thread.

 

 

Most non-physicists consider the two to be identical - and, if you never leave the surface of the earth, they're as near to right as makes no difference.