B Does Relativistic Mass Affect the Way We Weigh Things?

[MarkSK]

Hi everyone.
I have some questions related to relativistic mass: Does atoms and molecules are affected by this relativistic effects? and does relativistic mass affects the way we weigh things?
What I mean is; (and based on my limited knowledge of Special and General Relativity ) atoms an molecules have more (or less) kinetic energy in relation to temperature and pressure, so, if these particles move then there may be some relativistic effects going on, right?

I know we can calculate the relativistic mass using:

But the tricky thing is the speed of individual atoms (or molecules)

So, the point is, do these relativistic effects affect atoms? and does this affect the way that a chemist might try to weigh a substance?

Beware that I don't know much about relativity, so I'd love to know where is the problem in my reasoning

 

[Herman Trivilino]

does relativistic mass affects the way we weigh things?

No. Relativistic mass has no effect on anything because it's not physical. It's just a definition of a term. Originally researchers thought it might be a genuine relativistic generalization of the concept of mass, but it soon became quite clear that that was not to be the case. That was over 100 years ago. The term stuck, however, and didn't start to disappear from the college-level introductory physics textbooks until the 1990's. Since that time it has virtually disappeared.

So, the point is, do these relativistic effects affect atoms? and does this affect the way that a chemist might try to weigh a substance?

No. The effect is too small for a chemist to have to worry about. It won't show up because the scales used to weigh stuff are not precise enough.

It does effect the energy levels of atomic electrons in the heaviest of atoms to an extent that can be measured.

 

[atyy]

No. Relativistic mass has no effect on anything because it's not physical.

Relativistic mass is physical in the same way that energy is physical.

 

[jtbell]

So, the point is, do these relativistic effects affect atoms? and does this affect the way that a chemist might try to weigh a substance?

When you add energy to an object by heating it, its mass increases. However, as Mister T noted, this effect is too small to be measurable in practice.

Consider a 100 g (0.1 kg) chunk of copper. Heat it enough to raise its temperature by 1000°C, which brings it to just below the melting point if you start from room temperature. Look up the specific heat of copper and calculate the amount of energy added. Then use E = mc² to calculate the corresponding increase in mass.

How many decimal places of precision would a scale have to have, in order to register this increase?

 

[Orodruin]

First of all, I suggest that you read this. It will tell you why physicists today generally do not talk about relativistic mass (short version: it is not very useful as a "mass" and it is in essence just the total energy of an object rescaled by $1/c^2$).

Second, if you have a composite object, such as an object made out of several atoms as you took as an example, what matters for its mass is the total energy it has in its rest frame (this is the mass-energy equivalence). If its parts are moving in the object's rest frame (such as thermal motion of atoms), then also the kinetic energy of the parts (as well as their rest masses and any binding energy) contribute to this mass.

 

[MarkSK]

Thanks a lot for the answers!

First of all, I suggest that you read this. It will tell you why physicists today generally do not talk about relativistic mass (short version: it is not very useful as a "mass" and it is in essence just the total energy of an object rescaled by $1/c^2$).

Thanks, Orodruin, I'll take a look at your post.