# Does HEAT have mass?

1. Sep 8, 2011

### kkskarin

Does HEAT have mass??

Does HEAT have mass??

2. Sep 8, 2011

### LJW

Re: Temperature

Just going to clear up first, that heat is the transfer of energy in a thermodynamic system, and is not temperature.

No- heat, being a transfer or energy, does not have mass.

Temperature is derived from the average energy of particles in the medium, and has no effect on mass, nor does it have mass.

This could be proven simply in everyday terms. Think about it- if you had an object at a given temperature (assuming the temperatures are feasible and normal, and there are no reactions that take place- inert atmosphere) and weighed it, then heated it up a bit, and weighed it again, the mass would be the same.

Density however may change with temperature at larger scales.

Edit: Note that heat may be transferred through different means, for example electromagnetic radiation. These particles created directly by the kinetic energy of the particles is massless, however heat may be transferred through a preexisting medium which can have mass, but its mass is not as a result of the temperature or transfer of heat.

3. Sep 8, 2011

### kkskarin

Re: Temperature

Then why does Earth absorbs heat from the sun whereas space remains cool?

4. Sep 8, 2011

### LJW

Re: Temperature

As I stated, heat may be transferred through different means. One of these is electromagnetic radiation (there is practically nil convection through space, being predominantly vacuum). Electromagnetic waves, as I stated, can be produced directly from "heat", or the kinetic energy of particles.

However, these electromagnetic waves are massless.

5. Sep 8, 2011

### kkskarin

Re: Temperature

Thank You. :)

6. Sep 8, 2011

### jetwaterluffy

Re: Temperature

Temperature is based on the average kinetic energy in an area of space so does not have a mass, but is based on momentum. However, heat can be turned into mass via Einstein's energy-mass equivalence, E=mc^2.
Because space is almost completely transparent, so transmits the elecromagnetic radiation rather than absorbing it. The earth, meanwhile, being opaque, absorbs a lot of the radiation, changing it into heat, which warms the planet up.

7. Sep 8, 2011

### Drakkith

Staff Emeritus
Re: Temperature

Whoa, hold on all. According to my knowledge, and recent PF posts, an object at a higher temperature DOES have more mass than at a lower temp.

Space is mostly empty of matter while the Earth is not. The light sent from the Sun has to be absorbed by something to heat it up, and since space is mostly empty there isn't much to actually absorb the light. There IS matter in space, but the amount is vastly less than the atmosphere of the Earth. The average density of matter in intergalactic space is a few atoms per cubic meter, while the atmosphere of the Earth at sea level is 10^25 atoms per cubic meter. (Thats 10 with 25 zeroes afterwards)

Space can't have a temperature, but anything that occupies it does. Note that often it is said that the temperature of space is about 4 kelvin or so, but that is simply the temperature of the Cosmic Microwave Background, not space itself.

8. Sep 8, 2011

### Andrew Mason

Re: Temperature

Are you asking 1. whether heat has mass, 2. whether only mass (matter) has heat, or 3. whether heat added to an object increases its mass?

AM

9. Sep 9, 2011

### kkskarin

Re: Temperature

Im asking "Does heat has *** or not?"

10. Sep 9, 2011

### Drakkith

Staff Emeritus
Re: Temperature

I'm assuming that is "Does heat have mass or not".

All I can say is that an object at a higher temperature does have more mass than a cooler object.

11. Sep 9, 2011

### Ken G

Re: Temperature

I think it depends on whether we mean inertial/gravitational mass, for which the answer is "yes", or rest mass, for which the answer is "no."