# B Heat

1. Oct 4, 2016

### Ali Abbas

I dont understand what is heat actually. And what are the physical constituents that make up this entity.

2. Oct 4, 2016

### Staff: Mentor

Welcome to PF!

Heat is not a physical "thing". It is the name given to thermal energy in transit.
https://en.wikipedia.org/wiki/Heat

3. Oct 4, 2016

### Ali Abbas

According to you, heat is the transit of thermal energy from a higher temperature body to a lower temperature body. I accept your statement about heat, but unfortunately it doesn't satisfy my curiosity. Its because what you stated above defines the flow of heat or exchange of thermal energy, but what actually is thermal energy?

4. Oct 4, 2016

### Staff: Mentor

There is a wiki article for that too, though it is a bit more complicated since there is more than one source for the energy (such as kinetic energy and chemical potentail energy): https://en.wikipedia.org/wiki/Thermal_energy

5. Oct 4, 2016

### Ali Abbas

The above definition applies for classical thermodynamics. But what i want to know about heat or thermal energy is its nature, source of existance and the physical properties like density, nature or form, propogation technique, dimensions and density.

6. Oct 4, 2016

### Efrain Garcia

Heat is the energy and random motion of particles. Temperature is the measurement of that motion. For example, the less a particle vibrates, the "colder" it is. The more a particle moves, the "hotter" it is. The distribution of heat across many particles is simply the system trying to become equal.

7. Oct 4, 2016

### Staff: Mentor

"its nature" and "source of existance" is simply what we define it to be. But it doesn't have a physical form. It seems like you are expecting energy to be something it is not. We do get people confused or unsatisfied about this fairly often.

8. Oct 4, 2016

### Ali Abbas

thanks for the answer, this is something i was looking for. And it clarifies simply the whole concept.

9. Oct 4, 2016

### Ali Abbas

Still gotta know how thermal energy propogates in vaccuum? And what form of matter is thermal energy made up of. I am using the word 'matter' here because heat can cause variations in dimensions in other bodies of matter without direct contact. This is a property which has similar effects of 'force'. And force is an effect caused by involvement of mass, and mass is a quantity of matter present. Therefore i assume heat to be a non-contact force

10. Oct 5, 2016

### Efrain Garcia

Heat doesn't need other molecules in order to propagate. In a vacuum, particles can lose quantum kinetic energy (heat) by giving off photons. We see this as infrared light, UV, visible light, etc. Heat doesn't have mass, it is used to describe energy. There is no particle that carries heat, heat is a property of particles. And can you elaborate on what you mean by "heat can cause variations in dimensions in other bodies... Without contact"?

11. Oct 5, 2016

### Ali Abbas

It means changes is, shape, size, chemical configuration(ex:-combustion,burning,etc) , melting, push away objects in a particular direction. All these are the effects of 'force' , more likely 'non-contact force'.

12. Oct 5, 2016

### Drakkith

Staff Emeritus
Bodies in a vacuum can lose or gain energy by giving off or absorbing electromagnetic radiation. The internal energy gained or lost this way is usually thermal energy.

Thermal energy is not made up of anything. It's simply a way to describe certain properties of matter.

Heat is not a force at all. It is the transfer of energy from one object to another via convection, conduction, or radiation.

You're mixing up different terms and concepts. Heat is not a force, nor are any of those things "dimensions" of an object.

This isn't correct. Heat is not "quantum kinetic energy".

13. Oct 5, 2016

### 256bits

As said before, heat is not a substance.
It is the transfer of energy from one system to another, through a process other than work.
You seem to keep insisting that heat has some property in and of itself.
That is an old out dated viewpoint unacceptable by today's knowledge.

14. Oct 5, 2016

### Efrain Garcia

Well, it is a particles movement. Ergo, kinetic energy. It can lose some of this energy by bumping into other atoms, giving off some of that energy directly, or give off photons, decreasing it's kinetic energy. That's why electrons and other particles more when excited by absorbing photons.