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# (GCSE) This might be an absolutely stupid question, but... Watch

1. if you compress a gas enough, can you change its state?
2. Depending on where the triple point is and the temperature, yes. Typically into a liquid.
3. (Original post by Simes)
Depending on where the triple point is and the temperature, yes. Typically into a liquid.
Please can you explain what a triple point is? Remember that I'm only at GCSE level.
4. Melt a solid, like metal or ice, and you get a liquid such as molten steel or water.

Heat a liquid such as water and it bubbles off as a gas.

Going in the other direction the same thing happens: water turns to ice and propane and butane become a fluid called Liquefied Petroleum Gas (LPG) to be sold in cigarette lighters or big metal containers for patio heaters.

As well as temperature, pressure can be used too. A squashed gas becomes a liquid, a squashed liquid becomes a solid. Squirt a liquid into a vacuum and it will turn into a gas (once it has warmed up, anyway).

There is an interaction between temperature and pressure which is elegantly simple.

But carbon dioxide does something weird. We know it as a gas, but when you chill it, it turns into a solid which we call "dry ice". When dry ice is heated, it turns straight into gaseous carbon dioxide - it does not go through the liquid state. It turns out this applies to all / most (not sure which, can't remember) gases. If the pressure and temperature are low enough, it goes straight from solid to gas and back again. And if you get the pressure and temperature just right, adjusting either by a tiny amount makes the substance flick between gas, solid or liquid as appropriate.

For carbon dioxide, this point where it can be all three things - the triple point - is warmer then room temperature. For water, it happens just below zero Celsius.

(That might be a load of old toffee - I did it from memory. I bet Google can find you better plain English explanations. With pictures too.)

Yes, and then there's water, which does not behave properly and is different from almost everything else in that solid water (ice) floats on liquid water. That has huge consequences and is one of the reasons we have life on Earth. If you want evidence there is some supreme creator, water is a clue that the current universe was one of the failed prototypes that didn't quite work and fiddling with the physical properties of water was a necessary kludge to make this universe even get started. :-) But don't put that in your Physics homework!
5. (Original post by Simes)
Yes, and then there's water, which does not behave properly and is different from almost everything else in that solid water (ice) floats on liquid water. That has huge consequences and is one of the reasons we have life on Earth. If you want evidence there is some supreme creator, water is a clue that the current universe was one of the failed prototypes that didn't quite work and fiddling with the physical properties of water was a necessary kludge to make this universe even get started. :-) But don't put that in your Physics homework!
That's quite incredible. You've taken something which is really rather trivial to explain and very well understood and turned it to an argument for creation. Wow.

(Original post by flibber)
Please can you explain what a triple point is? Remember that I'm only at GCSE level.
The triple point is the point at which the three phases coexist in equilibrium. It's a fixed point, i.e. at a specific pressure and temperature: for water Pressure=610 Pascals and Temperature=273.16 Kelvin
6. (Original post by langlitz)
That's quite incredible. You've taken something which is really rather trivial to explain and very well understood and turned it to an argument for creation. Wow.
I knew I should have put a huge smiley in there. :-) I meant it to read as "If there is a creator, this universe is a right ****-up. Definitely an early attempt".

Space is mostly empty, that can't be right. What was the point of that?

Ice should sink, not float.

Black holes - oops, overdid it on the "gravity increases with mass" formula.

Parasitic wasps. Seriously, created by a perfect being?

Cancer. So much evidence for evolution, in everyone's face, every day.

If a great spectral being made the universe, he/she/it got an E and told to do extra homework.
7. (Original post by Simes)
Melt a solid, like metal or ice, and you get a liquid such as molten steel or water.

Heat a liquid such as water and it bubbles off as a gas.

Going in the other direction the same thing happens: water turns to ice and propane and butane become a fluid called Liquefied Petroleum Gas (LPG) to be sold in cigarette lighters or big metal containers for patio heaters.

As well as temperature, pressure can be used too. A squashed gas becomes a liquid, a squashed liquid becomes a solid. Squirt a liquid into a vacuum and it will turn into a gas (once it has warmed up, anyway).

There is an interaction between temperature and pressure which is elegantly simple.

But carbon dioxide does something weird. We know it as a gas, but when you chill it, it turns into a solid which we call "dry ice". When dry ice is heated, it turns straight into gaseous carbon dioxide - it does not go through the liquid state. It turns out this applies to all / most (not sure which, can't remember) gases. If the pressure and temperature are low enough, it goes straight from solid to gas and back again. And if you get the pressure and temperature just right, adjusting either by a tiny amount makes the substance flick between gas, solid or liquid as appropriate.

For carbon dioxide, this point where it can be all three things - the triple point - is warmer then room temperature. For water, it happens just below zero Celsius.

(That might be a load of old toffee - I did it from memory. I bet Google can find you better plain English explanations. With pictures too.)

Yes, and then there's water, which does not behave properly and is different from almost everything else in that solid water (ice) floats on liquid water. That has huge consequences and is one of the reasons we have life on Earth. If you want evidence there is some supreme creator, water is a clue that the current universe was one of the failed prototypes that didn't quite work and fiddling with the physical properties of water was a necessary kludge to make this universe even get started. :-) But don't put that in your Physics homework!

(Original post by langlitz)
That's quite incredible. You've taken something which is really rather trivial to explain and very well understood and turned it to an argument for creation. Wow.

The triple point is the point at which the three phases coexist in equilibrium. It's a fixed point, i.e. at a specific pressure and temperature: for water Pressure=610 Pascals and Temperature=273.16 Kelvin

(Original post by Simes)
I knew I should have put a huge smiley in there. :-) I meant it to read as "If there is a creator, this universe is a right ****-up. Definitely an early attempt".

Space is mostly empty, that can't be right. What was the point of that?

Ice should sink, not float.

Black holes - oops, overdid it on the "gravity increases with mass" formula.

Parasitic wasps. Seriously, created by a perfect being?

Cancer. So much evidence for evolution, in everyone's face, every day.

If a great spectral being made the universe, he/she/it got an E and told to do extra homework.
Thanks to both of you for your help. Maybe the reason why we haven't heard from God for almost 2500 (Judaism) or 2000 years (Christianity) (or 1400 in the case of Islam) is because he's given up on this experiment of his and has created another Universe!~

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