runny4
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What is the difference between kinetic and thermal energy because aren't they both due to the movement of molecules and subsequently give off heat?
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lerjj
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(Original post by runny4)
What is the difference between kinetic and thermal energy because aren't they both due to the movement of molecules and subsequently give off heat?
yes, ultimately they're both due to the motion of particles. But the distinction (when it is drawn, that is) is that kinetic energy involves visible movement in the form of either the CoM moving, the object rotating, vibrating etc. Whereas thermal energy is less detectable.

It's just a convenience - instead of looking at each particle and summing their kinetic energies using \dfrac{p^2}{2m} you can measure the temperature of the object and calculate the total kinetic energy using statistical techniques (I haven't done any real thermodynamics is, E=kT the correct eq. here?)
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Kallisto
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(Original post by runny4)
What is the difference between kinetic and thermal energy because aren't they both due to the movement of molecules and subsequently give off heat?
The thermal energy means the energy which exists in atoms, molecules or another substances during entropy. As these ones are in movement, kinetic energy exists too. And that is to say that these energies depends on each other. According to the heat in a thermodynamic system, it influences these energies. If heat is added in this system, the kinetic energy of atoms, molecules etc increases and thus the thermal energy as well. But if the head is subtracted in this system, both the kinetic and thermal energy decrease.

So you can say that these energies are the result of the movements of the particles during heat exposure. But the difference is that kinetic energy is visible because of the movement, while thermal energy is invisible, as this energy is quasi in existence in the inner of particles and so carry with one.
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runny4
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(Original post by Kallisto)
The thermal energy means the energy which exists in atoms, molecules or another substances during entropy. As these ones are in movement, kinetic energy exists too. And that is to say that these energies depends on each other. According to the heat in a thermodynamic system, it influences these energies. If heat is added in this system, the kinetic energy of atoms, molecules etc increases and thus the thermal energy as well. But if the head is subtracted in this system, both the kinetic and thermal energy decrease.

So you can say that these energies are the result of the movements of the particles during heat exposure. But the difference is that kinetic energy is visible because of the movement, while thermal energy is invisible, as this energy is quasi in existence in the inner of particles and so carry with one.
thanks
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Kallisto
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(Original post by runny4)
thanks
You are welcome. The main point for me is that you got it. If you have another questions or another problems in understanding, let me know.
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runny4
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(Original post by lerjj)
yes, ultimately they're both due to the motion of particles. But the distinction (when it is drawn, that is) is that kinetic energy involves visible movement in the form of either the CoM moving, the object rotating, vibrating etc. Whereas thermal energy is less detectable.

It's just a convenience - instead of looking at each particle and summing their kinetic energies using \dfrac{p^2}{2m} you can measure the temperature of the object and calculate the total kinetic energy using statistical techniques (I haven't done any real thermodynamics is, E=kT the correct eq. here?)
I havent done thermodynamics either but tell me if i am wrong the main point is that kinetic energy is easier to detect than heat?
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lerjj
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(Original post by runny4)
I havent done thermodynamics either but tell me if i am wrong the main point is that kinetic energy is easier to detect than heat?
On a particle by particle level, you only have two types of energy: kinetic and potential. When you start dealing with larger concepts like a gas, some of the kinetic energy is not easy to measure, but a direct consequence of it (the temperature) is, so you invent the concept of "thermal energy", and then later realise it's the same thing as kinetic.

You could probably say that kinetic energy is easier to detect than heat, but that would need a few qualifying remarks - for instance you can clearly detect that a lightbulb that's been left on for a while is hot. What you can't detect in this case, is that the tungsten atoms are vibrating wildly. I'd say that kinetic energy is more directly observable.
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runny4
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(Original post by Kallisto)
The thermal energy means the energy which exists in atoms, molecules or another substances during entropy. As these ones are in movement, kinetic energy exists too. And that is to say that these energies depends on each other. According to the heat in a thermodynamic system, it influences these energies. If heat is added in this system, the kinetic energy of atoms, molecules etc increases and thus the thermal energy as well. But if the head is subtracted in this system, both the kinetic and thermal energy decrease.

So you can say that these energies are the result of the movements of the particles during heat exposure. But the difference is that kinetic energy is visible because of the movement, while thermal energy is invisible, as this energy is quasi in existence in the inner of particles and so carry with one.
I understand the majority of what you said but i don't understand
thermal energy is invisible, as this energy is quasi in existence in the inner of particles and so carry with one
what do u mean carry with one?
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Kallisto
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(Original post by runny4)
I understand the majority of what you said but i don't understand
thermal energy is invisible, as this energy is quasi in existence in the inner of particles and so carry with one
what do u mean carry with one?
I see. Okay, here we go again with explanation.

Look: When a particle (atom or molecule) is in movement, the particle is spending kinetic energy all the time, as long as the movement continues. But during this movement, the particles have thermal energy 'in them', that is why the thermal energy is everywhere where the particles are moved. This form of energy is quasi 'dragged' by particles. That is what I meant when I was talking about 'carry with one'.

In terms of invisible thermal energy, you have to know that this form of energy is invisible for human eyes. The thermal energy (as heat) which is in existence in the inner of the particles has a wave length in infrared range. This range is out of the visible light for humans. To name some examples and to give you a clearer imagination, just think about a flame of a candle which is spreading thermal energy as heat around it. The same applies to life forms like humans or animals which are spreading heat in their surroundings. To make this form of energy visible, you need an infrared camera.

By the way when particles are in movement, they emitted thermal energy in their surrounding, as long as heat exposure and their movement goes on.
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runny4
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(Original post by Kallisto)
I see. Okay, here we go again with explanation.

Look: When a particle (atom or molecule) is in movement, the particle is spending kinetic energy all the time, as long as the movement continues. But during this movement, the particles have thermal energy 'in them', that is why the thermal energy is everywhere where the particles are moved. This form of energy is quasi 'dragged' by particles. That is what I meant when I was talking about 'carry with one'.

In terms of invisible thermal energy, you have to know that this form of energy is invisible for human eyes. The thermal energy (as heat) which is in existence in the inner of the particles has a wave length in infrared range. This range is out of the visible light for humans. To name some examples and to give you a clearer imagination, just think about a flame of a candle which is spreading thermal energy as heat around it. The same applies to life forms like humans or animals which are spreading heat in their surroundings. To make this form of energy visible, you need an infrared camera.

By the way when particles are in movement, they emitted thermal energy in their surrounding, as long as heat exposure and their movement goes on.
ok thanks i get it
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Kallisto
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(Original post by runny4)
ok thanks i get it
You are welcome. I always pleased to help someone with my explanations.
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