Eli5 If putting something under pressure increases the temperature why is the bottom of the ocean so cold?
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Because the pressure is not great enough to affect it. You would have to go much deeper beyond the crust of the earth.
Increasing pressure only definitively increases the temperature if all other variables remain the same. If the other variables change then that affects the degree to which the temperature changes. Water’s density changes with temperature to a maximum density at around 4°C, so the colder water has more molecules in the same amount of volume to disperse the energy from the pressure than the amount of water in the same volume at a higher temperature.
The bottom of the ocean was put under pressure a long, long time ago. Plenty of time to lose any heat gained.
The ocean floor receives a little thermal energy from the Earth’s core, but that’s not a lot. And it gets very little from the source that most of the surface benefits from…the sun.
Because the pressure is not great enough to affect it. You would have to go much deeper beyond the crust of the earth.
Increasing pressure only definitively increases the temperature if all other variables remain the same. If the other variables change then that affects the degree to which the temperature changes. Water’s density changes with temperature to a maximum density at around 4°C, so the colder water has more molecules in the same amount of volume to disperse the energy from the pressure than the amount of water in the same volume at a higher temperature.
The bottom of the ocean was put under pressure a long, long time ago. Plenty of time to lose any heat gained.
The ocean floor receives a little thermal energy from the Earth’s core, but that’s not a lot. And it gets very little from the source that most of the surface benefits from…the sun.
The pressure isn’t what causes the heat, it’s the change in pressure that causes a change in temperature.
The bottom of the ocean has been under pressure long enough that any heat that the creation of the pressure created has long since dissipated. The bottom of the ocean is so cold because there is simply nothing to heat it up. The sun can only heat the surface of the ocean, and only small parts of the ocean floor have volcanic vents.
The pressure isn’t what causes the heat, it’s the change in pressure that causes a change in temperature.
The bottom of the ocean has been under pressure long enough that any heat that the creation of the pressure created has long since dissipated. The bottom of the ocean is so cold because there is simply nothing to heat it up. The sun can only heat the surface of the ocean, and only small parts of the ocean floor have volcanic vents.
The act of increasing the pressure increases the temperature increases the temperature under the right conditions however once something has been pressurised, the temperature will slowly equalise with the surroundings to balance the heat absorbed vs heat lost. Waters relative impressibility also reduces this effect as the increase in temperature is basically coming from retaining all the energy that was in the volume of material and cramming it into a smaller space so you now have more energy per unit of volume. This is generally represented with the [ideal gas law](https://en.wikipedia.org/wiki/Ideal_gas_law) which, as the name suggests, doesn’t work in the same way to liquids like water
Because it is a fluid, there is flow that keeps the water at its maximum density at the bottom which for many liquids would mean the coldest material sinks and the warmest stays on top however water is a bit special as it has a maximum density at 4^(o)Cs so the coldest and hottest water want to rise leaving the bottom of the ocean at that temperature.
All of the above answers are correct, however I would add that the increase in pressure is not enough, the substance must be compressed. Water is not “compressible”* in the same way as say, air … though sea water is somewhat more compressible than pure water, it world be essentially compressed to its maximum in a dixie cup.
*https://www.usgs.gov/special-topics/water-science-school/science/water-compressibility#:~:text=squeeze%22%20on%20water-,Water%20is%20essentially%20incompressible%2C%20especially%20under%20normal%20conditions.,back%22%20out%20of%20the%20straw.
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