Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: NeT-HeaD on 10/06/2017 22:56:22
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How exactly does heat radiation/transferral relate to gravity? At the surface it seems to be , cuz in general we say heat rises but my gut says otherwise that it's not related at all.
Who can explain the details of this 'process' at molecular level?
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Hot air is less dense than cold air, that is why it rises above cold air. You could also see it as cold air sinking and displacing the hot air below it.
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Hot air is less dense than cold air, that is why it rises above cold air. You could also see it as cold air sinking and displacing the hot air below it.
Ye . that i know. But thats not the heat behaving . This is heated air opposed to cooled air. I want to know what happens at the smallest level of molecules when heat travels from one place to another. what partical is doing that. Does it have mass . Can it be slowed down or accelerated by gravity . Thats my area of darkness that i would like to see luminated so to speak :o
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The first thing to say is that in normal usage, heat and temperature are used interchangeably.
In Physics, they are quite different things, and the amount of heat in a substance is proportional to its mass and (sort of) proportional to its temperature (if you ignore phase changes).
The strength of Gravity is proportional to the mass of an object, and the distance to that object. For us on Earth, we usually stand on the surface of the Earth, and the average distance is the radius of the Earth.
Both of the above mention mass, but in general gravity and temperature arise from different sources.
- You can have a supermassive black hole which has a temperature indistinguishable from absolute zero (in theory, the lowest possible temperature)
- Inside a fusion reactor experiment, you may have a very low mass like 1g of Hydrogen plasma (which produces a very weak gravitational force), but at temperatures of 100 million degrees.
There are also cases where gravity and temperature interact, for example the Sun's immense gravity holds the Sun together against the tendency of hot gas to expand and cool.
Maybe some other contributors can explain the distinctions better than I can?
Oops! Overlapping posts...
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Hot air is less dense than cold air, that is why it rises above cold air. You could also see it as cold air sinking and displacing the hot air below it.
Ye . that i know. But thats not the heat behaving . This is heated air opposed to cooled air. I want to know what happens at the smallest level of molecules when heat travels from one place to another. what partical is doing that. Does it have mass . Can it be slowed down or accelerated by gravity . Thats my area of darkness that i would like to see luminated so to speak :o
Heat does not have mass, and is not made of anything.
At a basic level, temperature is best thought of as how much kinetic energy the molecules have on average. This includes how quickly the molecules are moving as well their internal motions (vibration and rotation at reasonable temperatures, and at very high temperatures this also includes changing the energy of the electrons).
Heat is the total amount of random kinetic energy of the molecules (non-random kinetic energy is extractable as work). Heat transfer is molecules with high kinetic energy slowing down by making other molecules speed up. Heat "flows" from hot to cold because the molecules with a lot of kinetic energy will never (what never? well, hardly ever) take kinetic energy from the molecules with less. Instead, the molecules with a lot of kinetic energy will always increase the kinetic energy of the molecules with less, until they even out.
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Whilst not an identical phenomena granular convection can illustrate sorting that can be related to the sorting of hot and cold gasses. Both involve kinetic energy. In the case of granular convection this is introduced by shaking or vibration. It can show that this system behaves much like a fluid. The atmosphere itself can be considered a type of fluid and can be modelled using fluid dynamics.
https://en.m.wikipedia.org/wiki/Granular_convection
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The first thing to say is that in normal usage, heat and temperature are used interchangeably.
In Physics, they are quite different things, and the amount of heat in a substance is proportional to its mass and (sort of) proportional to its temperature (if you ignore phase changes).
Your response is based on the common misconception that a body "contains" heat. This is incorrect. Heat is thermal energy in motion, i.e. Heat is the amount of energy flowing from one body to another spontaneously due to their temperature difference. You were thinking of thermal energy. A body can have/contain thermal energy, but not heat.
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Can (heat transfer) be slowed down or accelerated by gravity?
I am not aware of any cases where gravity directly accelerates or reverses heat transfer.
However, a flow of electrical current can accelerate or reverse heat flow, which is what happens in a Peltier junction cooler. You could imagine it as if the flow of electrons "sweeps along" the phonons (https://en.wikipedia.org/wiki/Phonon) which carry the heat. By selecting the direction of current flow, you can move heat from the "cold" side to the "hot" side, which is the opposite of the natural direction of heat flow.
Peltier junctions are often used for DNA multiplication using the PCR reaction (which requires cyclic heating and cooling) and high-power solid-state lasers (which require cooling).
See: https://en.wikipedia.org/wiki/Thermoelectric_cooling
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How exactly does heat radiation/transferral relate to gravity? At the surface it seems to be , cuz in general we say heat rises but my gut says otherwise that it's not related at all.
Who can explain the details of this 'process' at molecular level?
You made a mistake here. Heat doesn't rise. In fact it has no meaning for heat to rise. Heat is not a substance which can rise for fall. It is hot air that rises.