# Does Heat Have Mass? - Exploring the Connection Between Energy & Gravity

• brollysan
In summary: That heat is then transferred to the contents of the container and the atoms of that liquid/gas get active and start bouncing off each other and the walls of the container and so heat inside the container is produced.In summary, Increasing energy of a system increases its mass.
brollysan
Hi guys just something I am a bit curious about, if heat is a form of energy, doesn't it follow from the mass-energy equivalence that heat energy has mass, however small? Then does this mean that heat energy has gravity/can be affected by gravity?

I am curious about energy in general but heat was a bit harder to imagine, do the photons that carry thermal/EM energy from the sun to us have mass then?

I believe you are correct. Everything I've read says that increasing energy of a system increases its mass. According to my knowledge, all EM radiation has momentum and according to GR will have gravitation.

Yes, energy causes exactly the same gravitational effects as an equivalent amount of mass. The equations of general relativity include a mathematical object called the "stress-energy tensor" which encapsulates both mass and energy in the same way. Light does indeed produce its own (very meager) gravitational field.

- Warren

"Heat" is a measure of the kinetic energy of a system. Kinetic energy is a function of momentum, which will increase as the velocity increases. "Heat energy" again is just a measure of the kinetic energy of a system, so it is not necessarily carried by photons (rather by the interaction of molecules/atoms). Photons carry energy (They are little packets of energy), and this can be turned into kinetic energy (aka heat) by absorbtion.

When EM radiation is emitted from a hot object, it is doing so because of the atomic transitions that are going on within the object. As the object cools, the atoms go from an excited to ground state, and there is an emission of a photon because of that.

In short, I do not believe that heat is carried by photons, simply because the definition of heat is dependent on the kinetic energy of a particle, and the kinetic energy of a photon is zero (but their momentum is a finite number, dependent on the wavelength/ frequency). However, the energy that is carried in the EM wave CAN be CONVERTED into heat.

I am not 100% of what I just claimed but I hope it makes sense...

Heat doesn't have mass but it contributes to the mass of matter by adding energy to it. The photons that carry heat energy gravitate and are affected by gravity, they do not have mass.

cosmik debris said:
Heat doesn't have mass but it contributes to the mass of matter by adding energy to it.
I don't see the distinction.

The term heat has various meanings, but I think we can all agree that the energy of a system which determines its heat and temperature and all that does have mass. A hotter object has more energy in it and is therefore more massive than a similar system which is at a cooler temperature.

Agreed, but the "heat" itself does not have mass. The energy added to increase the temperature increases the mass of the object.

Heat energy as a stand alone product does not exist as far as I understand. The only way energy can be called heat is when discussing temperature, kinetic energy of the molecules, or a transfer of that kinetic energy.

Isn't that what I just said?

Upon rereading it appears so, though the distinction that the energy that is called heat does not have mass doesn't seem explicit.

Energy density effectively curves space - time as per the energy momentum tensor.

Drakkith said:
Everything I've read says that increasing energy of a system increases its mass.

and all the msgs from others since...

OK I am totally confused. how can increasing energy of a system by heating it, increase its mass ?

take an enclosed container of whatever... liquid , gas... its a fixed amount
you heat it over a flame... that heat gets the atoms in the container material in motion and they (according to Feynman) start bouncing off each other and heat is produced. That heat is then transferred to the contents of the container and the atoms of that liquid/gas get active and start bouncing off each other and the walls of the container and so heat inside the container is produced.

Assuming I haven't totally screwed up there (always possible ;) ) you have a fixed amount of gas etc in the container .. HOW can it increase in mass ? its a fixed amount

Dave

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Now I can accept that in the case of physically bombarding a material with particles... electrons, photons etc then yes you are adding physical mass to the original material.

But in my understanding, that isn't happening with just pure heating ... radiated heat

Dave

I believe it is shown in E=MC^2

davenn said:
take an enclosed container of whatever... liquid , gas... its a fixed amount
you heat it over a flame... that heat gets the atoms in the container material in motion and they (according to Fyenman) start bouncing off each other and heat is produced. That heat is then transferred to the contents of the container and the atoms of that liquid/gas get active and start bouncing off each other and the walls of the container and so heat inside the container is produced.

Assuming I haven't totally screwed up there (always possible ;) ) you have a fixed amount of gas etc in the container .. HOW can it increase in mass ? its a fixed amount

If you do the calculations you will find that it takes more force to accelerate a box containing a hot gas than it does to accelerate the same box containing the same amount of cold gas. By f=ma since a greater f is required for the same a that means that m is greater.

DaleSpam said:
If you do the calculations you will find that it takes more force to accelerate a box containing a hot gas than it does to accelerate the same box containing the same amount of cold gas. By f=ma since a greater f is required for the same a that means that m is greater.

hey Dale,

I can't accept that on face value, I would have to see the working for that. As it doesn't answer my basic question. How can a fixed amount of matter be more massive just becauser its hotter? there have been no physical particles added to increase its mass, where's the extra mass coming from ?

posted in the interests of learning :)

Dave

davenn said:
and all the msgs from others since...

OK I am totally confused. how can increasing energy of a system by heating it, increase its mass ?

take an enclosed container of whatever... liquid , gas... its a fixed amount
you heat it over a flame... that heat gets the atoms in the container material in motion and they (according to Fyenman) start bouncing off each other and heat is produced. That heat is then transferred to the contents of the container and the atoms of that liquid/gas get active and start bouncing off each other and the walls of the container and so heat inside the container is produced.

Assuming I haven't totally screwed up there (always possible ;) ) you have a fixed amount of gas etc in the container .. HOW can it increase in mass ? its a fixed amount

Dave

E=MC^2, so heating up your gas by the degree you're imagining will increase mass by that ammount, divided by the speed of light squared. It's a ridiculously tiny amount of mass, and I don't think you're used to thinking in such a small scale.

davenn said:
I can't accept that on face value, I would have to see the working for that.
Sorry that you can't accept that. I don't have the time to work it out this week, so if you really want to see it you will have to work it yourself. It is tedious but not that difficult, simply calculate the weight of a box of ideal gas and see that it depends on the temperature.

davenn said:
As it doesn't answer my basic question. How can a fixed amount of matter be more massive just becauser its hotter? there have been no physical particles added to increase its mass.
I think you misunderstand mass. Mass is a property that material objects have, but that doesn't mean that mass is only associated with matter. Similarly with energy, energy is a property that material objects have, but non-material things such as fields and photons also have energy. You can add energy without adding matter, similarly you can add mass without adding matter.

Did you realize that most of the mass of ordinary matter is not in the matter (fermions) itself but in the forces (bosons) that hold the matter together? That is one reason why nuclear reactions can convert mass into energy.

hillzagold said:
E=MC^2, so heating up your gas by the degree you're imagining will increase mass by that ammount, divided by the speed of light squared. It's a ridiculously tiny amount of mass, and I don't think you're used to thinking in such a small scale.

no that's not the problem

Dave

DaleSpam said:
Sorry that you can't accept that. I don't have the time to work it out this week, so if you really want to see it you will have to work it yourself. It is tedious but not that difficult, simply calculate the weight of a box of ideal gas and see that it depends on the temperature.

dunno where to start on that one ;)

I think you misunderstand mass. Mass is a property that material objects have, but that doesn't mean that mass is only associated with matter. Similarly with energy, energy is a property that material objects have, but non-material things such as fields and photons also have energy. You can add energy without adding matter, similarly you can add mass without adding matter.

yes probably ;) ... ok I understand photons having more energy than others but are still just a photon

visible light photon has more energy than a microwave one, a gamma ray photon more energy than a visible light photon.

Did you realize that most of the mass of ordinary matter is not in the matter (fermions) itself but in the forces (bosons) that hold the matter together? That is one reason why nuclear reactions can convert mass into energy.

ok, but in any given atom all those things are present within the atomic structure?
what is being added to change the mass of that structure ?

ok a physics lesson... so you are saying its the Bosonic force that holds the atoms of a particular element together ?

Crap ;) we are getting in much deeper than I ever did in 1st year university physics so so long ago :)

cheers
Dave

PS ok taking the E=MC^2 if the amount of energy in a system increases, as the speed of light is a constant, the only thing left means that the mass has increased. that's logical.

still leaves me trying to understand where the additional mass has come from in a closed system

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How good is your understanding of E=MC^2?

davenn said:
Any work that you do on or energy that you add to an object which does not increase its momentum will increase its mass. So heating an object up, making it spin faster, making its internal structure more energetic (charging up a battery, compressing a spring, etc.).

davenn said:
ok a physics lesson... so you are saying its the Bosonic force that holds the atoms of a particular element together ?
Yes, for example, a proton has a mass of 938 MeV/c² and is composed of 2 up quarks and 1 down quark. The up quarks have a mass of 2.4 MeV/c² each and the down quark has a mass of 4.8 MeV/c² for a total mass of 9.6 MeV/c² which is only about 1% of the mass of the proton. So the remaining 99% of the mass is not from the quarks, but from the energy (m=E/c²) in the strong force bonds holding the quarks together.

http://en.wikipedia.org/wiki/Proton
http://en.wikipedia.org/wiki/Standard_Model

So, th mass of ordinary material objects is not primarily due to the matter but due to the enormous amounts of energy in the forces holding the matter together. Similarly, any other energy that you add to an object (without increasing its linear momentum) will also increass its mass.

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Physics can be weird, you have to get your head around the fact that energy has mass, it isn't just something that matter has due to the fact that it is matter. You can read this Wiki page, I found it helpful and it has many examples:

http://en.wikipedia.org/wiki/Mass–energy_equivalence

DaleSpam said:
I don't see the distinction.

It does seem to be just playing with words but as I understand it the kinetic energy of the material's components due to temperature contribute to the mass of that material. I don't think you can say any energy has a mass. Certainly they can be converted back and forth but they are not the same. Not all kinetic energy contributes to mass, for example the kinetic energy of the body due to its overall motion doesn't, only the kinetic energy measured in the centre of momentum frame does. To further confuse things energy gravitates. I think perhaps the confusion arises from the 3 dimensional view where energy, mass, and momentum are different quantities. In 4-D spacetime they are all components of the energy-momentum tensor. In the simpler energy-momentum vector the zero component is E/c and the other three are momenta. The length of the vector is the mass. In combining them in this way we see there relationship in a more consistant way.

I think :-)

brollysan said:
Hi guys just something I am a bit curious about, if heat is a form of energy, doesn't it follow from the mass-energy equivalence that heat energy has mass, however small? Then does this mean that heat energy has gravity/can be affected by gravity?

I am curious about energy in general but heat was a bit harder to imagine, do the photons that carry thermal/EM energy from the sun to us have mass then?

Heat is not really a form of energy. Heat is the transfer of energy due to a difference in temperature. The energy moves from the object with the higher temperature to the object with the lower temperature. It doesn't disappear.

http://www.quitting-weed.net/"

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cosmik debris said:
Not all kinetic energy contributes to mass, for example the kinetic energy of the body due to its overall motion doesn't, only the kinetic energy measured in the centre of momentum frame does.
Sure, but that doesn't apply to heat or thermal energy.

Could you describe heat as the effect that energy has on an object?

DaleSpam said:
Sure, but that doesn't apply to heat or thermal energy.

That's what I said didn't I? The kinetic energy of the components of a body in the centre of momentum frame contribute to the mass. As you said somewhere else the binding energy, which is sort of negative) contributes more to the mass than the heat energy.

cosmik debris said:
That's what I said didn't I?
OK, so I think we have a substantive agreement and perhaps just a mild "phraseology" disagreement. I can leave it alone.

cosmik debris said:
The kinetic energy of the components of a body in the centre of momentum frame contribute to the mass. As you said somewhere else the binding energy, which is sort of negative) contributes more to the mass than the heat energy.
Yes, particularly the binding energy for the strong force.

## 1. Does heat have mass?

Yes, heat does have mass. Heat is a form of energy, and according to Einstein's famous equation E=mc², energy and mass are equivalent and can be converted into each other.

## 2. How is heat related to gravity?

Heat and gravity are both forms of energy and are related through Einstein's theory of general relativity. According to this theory, the presence of mass and energy creates a curvature in space-time, which is what we experience as gravity.

## 3. Can heat create its own gravity?

Technically, yes. As mentioned before, heat is a form of energy and any form of energy can create a gravitational field according to Einstein's theory of general relativity. However, the amount of heat needed to create a noticeable gravitational effect would be extremely large.

## 4. Is there a limit to the amount of heat that can be produced by an object?

There is no limit to the amount of heat an object can produce as long as it has a source of energy to convert into heat. However, there is a limit to the amount of heat an object can contain at a given time, which is known as its heat capacity.

## 5. What is the difference between heat and temperature?

Heat and temperature are closely related but they are not the same thing. Heat is a form of energy, while temperature is a measure of how hot or cold something is. Temperature is a result of the average kinetic energy of particles in a substance, while heat is the transfer of energy from a hotter object to a colder one.

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