– If the pressure at the bottom of the ocean is so extreme, are the molecules pushed closer together? If so, why isn’t it hotter, if the molecules are bumping into each other more?
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The molecules are moving slower, therefore are not generating as much energy or heat.
That and there is no sunlight to provide any additional thermal energy.
Yes, the molecules are pushed closer together. Not by much, because water isn’t very compressible, but still closer.
Temperature is basically the average kinetic energy of the molecules; bumping into each other more doesn’t mean higher temperature. Molecules going faster does. You may be thinking of the heating you get when you compress a gas suddenly…in that case, they *do* go faster because you’ve increased the energy in the system by compressing it and the energy had nowhere to go. Water in the ocean has plenty of places for energy to go…water has *huge* heat capacity…huge changes in energy result in very low changes in temperature. And, because it’s so in-compressible, there’s very little energy added in the compression.
They are. According to Wikipedia, water gets around 30kg/m^3 heavier in the deeper parts of the ocean.
If water sank from the surface, it would be heated up as it got squished smaller, but over time it would cool back down to the temperature of its surroundings as it exchanges heat with them.
The molecules may be closer together, but they’re always ‘touching’. Liquid water is not a gas where the molecules are freeballin’ all over the place. They’re shoulder to shoulder.
That aside, temperature doesn’t have to do with how often the molecules collide (even in a gas). It’s how much energy they have from moving around. Faster movement means more energy, but how often they bounce doesn’t change the energy.
this question seems very analogous to “If heat rises, why are mountains cold?”
But so you know: Heat is associated with LOW pressure, not high pressure. Heat makes things expand.
The molecules are pushed closer together, but not by much. Water is essentially “incompressible.”
An easy way to visualize that idea is picturing trying to make a block of concrete smaller by pushing on it between your hands. Neither the water, nor the concrete will change by any significant amount, no matter how hard you push. So, yes, the molecules are pushed closer together, but only by a super tiny amount.
As to the temperature thing, the water isn’t hotter for a few reasons.
First, energy is only added to something in the process of being compressed. If you took a chamber full of any gas and compressed it, then it would heat up. If you then left that box/chamber in a room for a while, the temperature of the gas would slowly change to match the ambient temperature of the room. Any temperature that may have been gained by the water at the bottom of the ocean by compression has long since been dispersed across the ocean.
Second, molecules being closer together isn’t what determines temperature; molecules colliding does.
Think of a room with a crowd of people. If the people are all running around really fast and smacking into each other, that would be a very hot temperature. If the people are all standing still, then the temperature would be very cold because they aren’t colliding.
If you shrunk the size of the room, but the people are still standing very still, then the amount/rate of collisions won’t change.
But surely the water at the bottom of the ocean will be ‘hotter’ as water is most dense at 4°C and becomes less dense as it cools, eventually floating once it becomes ice. This virtually unique property has supported life, in frozen bodies of water that can exist at four degrees, with a degree of insulation from the floating ice. Water is pretty amazing stuff, really…
Even though you got good answers, I’ll have to add to the temperature at the bottom. Because the water at the bottom of the ocean IS hotter than at the surface, if we only considered the effect of the pressure. This has lead to the creation of a property called “potential temperature” in ocean science, which corrects for this factor. Without this correction you couldn’t compare the temperature at e.i. 1000m depth to 5000m. This correction is often (at the bottom) in the order of 1 degree Celsius.
Now, the actual temperature at the ocean bottom is of course much colder than at the surface, because pressure is only a very small part of the whole, and other factors matter much much more.
You also have to consider why a package of water is at the bottom to begin with. It’s there cause it’s cold and salty (high density) and given those properties it has sunk below warmer, less salty water (low density).
Google the thermohaline circulation, it’s fascinating.
(I see a lot of comments saying it would have dissipated the tiny heat gain, that totally ignores why the package of water would even sink to begin with, and that heat is conducted very poorly in water at this scale, heat transfer is almost solely by convection hence the thermohaline circulation.)
Yes, things are closer together, but it’s a tiny effect. The electromagnetic force is many, many times stronger than gravity. Think of it like trying to compress a block of steel by standing on it.
For example, the density of the water at the surface under 1 atmosphere of pressure would be about 1000 kg per cubic meter, while in the Marianas Trench (about 1100 times the pressure), the volume would only be about 5% lower (about 1050 kg per cubic meter), a very small change for a very large increase in pressure. This isn’t nearly enough to generate significant heat, especially when it’s easily conducted into the atmosphere (which is wickedly cold in many places).
It was hotter. It cooled down over time. If the water suddenly all appeared there, the bottom would be significantly hotter. Over time the heat spreads out, and the top stays hot from the sun.
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