Eli5 If putting something under pressure increases the temperature why is the bottom of the ocean so cold?
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An increase in temperature doesn’t come “from” the pressure. When something (typically a gas) gets compressed, the existing heat gets concentrated into a smaller area. No heat is added to the system.
Water is (almost) non-compressible. No heat gets added, and (almost) no heat gets concentrated.
An increase in temperature doesn’t come “from” the pressure. When something (typically a gas) gets compressed, the existing heat gets concentrated into a smaller area. No heat is added to the system.
Water is (almost) non-compressible. No heat gets added, and (almost) no heat gets concentrated.
It’s not just putting “something” under pressure; you may be over-generalizing an effect that happens to gases to things that are not gases.
When you compress a gas, its temperature increases, unless it can conduct away perfectly or unless the compression happens slowly enough where the imperfect conduction available to that gas is sufficient to remove the heat. If the compression of a volume of gas is done fast enough where there isn’t enough time for the heat to leave the gas, that is called *adiabatic compression*. That is the kind of compression that is used to ignite the fuel that is sprayed into diesel engines. You can see it demonstrated here, in a transparent fire-piston, where sudden rapid compression heats the air in the cylinder up to the temperature where it can ignite char cloth (between 660˚F-850˚F):
#Bushcraft Tools | [Transparent Fire Piston – Explosive Flash](https://youtu.be/-39wmSBO2FM?t=5)
As far as I understand, compressing liquids does not result in the same heating. Liquids are largely incompressible. This doesn’t mean they can’t be under high pressure, just that the pressure doesn’t result in much volume change at all. And without much volume change, there won’t be much compressive heating, because this kind of heating is contingent on both pressure and volume reduction, not merely pressure.
It’s not just putting “something” under pressure; you may be over-generalizing an effect that happens to gases to things that are not gases.
When you compress a gas, its temperature increases, unless it can conduct away perfectly or unless the compression happens slowly enough where the imperfect conduction available to that gas is sufficient to remove the heat. If the compression of a volume of gas is done fast enough where there isn’t enough time for the heat to leave the gas, that is called *adiabatic compression*. That is the kind of compression that is used to ignite the fuel that is sprayed into diesel engines. You can see it demonstrated here, in a transparent fire-piston, where sudden rapid compression heats the air in the cylinder up to the temperature where it can ignite char cloth (between 660˚F-850˚F):
#Bushcraft Tools | [Transparent Fire Piston – Explosive Flash](https://youtu.be/-39wmSBO2FM?t=5)
As far as I understand, compressing liquids does not result in the same heating. Liquids are largely incompressible. This doesn’t mean they can’t be under high pressure, just that the pressure doesn’t result in much volume change at all. And without much volume change, there won’t be much compressive heating, because this kind of heating is contingent on both pressure and volume reduction, not merely pressure.
If you increase the pressure of something and leave it for 2 billion years, it’s probably cooled down.
If you increase the pressure of something and leave it for 2 billion years, it’s probably cooled down.
_Being_ under pressure has no effect on temperature, things do not stay hot on their own; that would actually be a very simple way to create infinite energy from a pressure cooker or a compressor.
_Changing_ pressure does not really change temperature either. This more or less holds for gases (and plasma), though. Why? Because:
What really changes temperature is getting _compressed_. That means more matter per volume. Gases get hotter when compressed, and they compress a lot when under pressure. Hence in total, gases get hot when putting them under pressure; but also their volume shrinks a lot. In the ideal case, the factor of compression causes the same factor in absolute (Kelvin!) temperature.
Meanwhile, liquids and solids are almost incompressible: they won’t compress notably under sane pressures. At the bottom of the oceans, water is roughly compressed by 1%. So, at best, it gets hotter by 1%, which starting at room temperature would mean a measly 3°C.
Other materials, especially solids, compress even less.
Source: I own a 300 atm compressor (for diving and such) and I assure you, nothing non-gaseous I ever put under such pressures got notably hot.
_Being_ under pressure has no effect on temperature, things do not stay hot on their own; that would actually be a very simple way to create infinite energy from a pressure cooker or a compressor.
_Changing_ pressure does not really change temperature either. This more or less holds for gases (and plasma), though. Why? Because:
What really changes temperature is getting _compressed_. That means more matter per volume. Gases get hotter when compressed, and they compress a lot when under pressure. Hence in total, gases get hot when putting them under pressure; but also their volume shrinks a lot. In the ideal case, the factor of compression causes the same factor in absolute (Kelvin!) temperature.
Meanwhile, liquids and solids are almost incompressible: they won’t compress notably under sane pressures. At the bottom of the oceans, water is roughly compressed by 1%. So, at best, it gets hotter by 1%, which starting at room temperature would mean a measly 3°C.
Other materials, especially solids, compress even less.
Source: I own a 300 atm compressor (for diving and such) and I assure you, nothing non-gaseous I ever put under such pressures got notably hot.
Friction from pressure squeezing things causes heat. Once that pressure equalizes it doesn’t increase heat energy as no energy transfer is still happening.
So the bottom of the ocean is so cold due to distance from sunlight.
Friction from pressure squeezing things causes heat. Once that pressure equalizes it doesn’t increase heat energy as no energy transfer is still happening.
So the bottom of the ocean is so cold due to distance from sunlight.
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