does heat hav mass?

Answer 1

Heat is a form of energy. Energy does not have mass.

Answer 2

By the way, please learn how to spell "have" in your questions. That kind of attention to detail will help you with your maths and physics, and other areas of learning.

Heat is a form of energy. More specifically, it is the vibrational energy of atoms. Something is hot because its atoms are vibrating. Something is hotter still because its atoms are vibrating even more rapidly and with a greater range of movement.

So heat is a (atomic) form of movement, and does movement have mass? Generally speaking, no. So no, heat does not have mass.

Incidentally, infrared radiation is NOT heat. It's radiation, yes, and can generate heat in matter when the radiation interacts with matter's atoms. Heat is transfered via infrared radiation.

Technically all energy can be associated with mass through the famous equation E=mc^2. But that has little relevance to this question, and it is fair to say that heat has no mass.

[Note to answerers coming later:

I didn't get the strongest impression from the question that questioner was about to design a nuclear reactor, consider energy flows inside a star, or worry about negative pressures causing inflationary forces in the first femtosecond of time. In other words, an answer involving stress-energy tensors and mass-energy equivalence hardly helps.

For high-school and classical physics, understanding the difference between mass and energy is vital, as is the idea of conservation of energy and conservation of mass. A simple question deserves an honest and simple answer - that the questioner will find useful in what they are doing or contemplating!

Quoting from general relatively, within this context, is to do with establishing answerer credibility, I think. And what is important here? Getting readers to think you're brilliant, or giving a good answer in the context of the question?

Anyway, the reactor analogy is not the best - its like saying my car weighs an extra 2500kg because that's how much gas I put into it in a year. Sure' that's what flows through the vehicle, but at any given time there's the same 25kg in the tank, on average. Similarly, the heat in a reactor is at a constant level, in equilibrium. The heat flow is part of the energy transfer amounting to 40,000 TJ (say) over one year.

Better to ask: what is the increase in mass of the reactor hardware due to the heat it possess while it operates? Doesn't this boil down to a mass increase for a given temperature?

So saying heat has mass - even a tiny amount - is unhelpful, I maintain, unless you are going to explain where that mass is, how much it is, and why. And this is a can of worms for high school science.

Of course, some will say that the "truth" must be told, but there's an awful lot of explaining to do to get to the point where it all makes sense.]

Answer 3

Yes. Every form of energy has an equivalent mass. Every form of mass, including that of energy (be it in radiation or atomic/molecular/grid vibrations like heat) gravitates. We account for it rather explicitly in the stress-energy tensor in general relativity.

No big deal.

I am not sure, though, why people who seem to know about the correct formula from special relativity fail to get the explanation right. But it seems as if almost everyone who answered before me did.

The mass loss from heat loss is macroscopic, by the way. Every nuclear power plant loses about 1kg of mass a year due to the heat that is given off by the fission or Uranium.

Answer 4

No. Heat is an electromagnetic radio wave in the infrared range, and electromagnetic waves are made up of massless particles known as photons.

Answer 5

Yes it does. Use E = mc^2 (or m = E/c^2) to work it out.

It is VERY small!