1. Classical physics predicts weight should NOT change at increasing temperatures and relativistic theory predicts weight should increase tiny immeasurable bit at increasing temperatures. I searched the literature and found several papers showing weight of metals actually DECREASES at increasing temperatures (Glaser 1990 Metrologia 27, Dmitriev 2003 Measurement Techniques 46). Glaser says AIR is responsible for changes in weight and Dmitriev thinks temperature also has an effect on weight. Could an experiment weighing a heated metal in VACUUM resolve the matter and test this fundamental prediction of traditional physics ?

2.

3. Are you referring to weight (force resulting from gravitational attraction) or mass?

4. Weight is referred to the readings of the balance.

5. For the air hypothesis :
If they meassured this in vacuumconditions where would the air come from ?
If they meassured in airy conditions what difference would it make for weight ?

I think (that,s how I learned it) the prediction is for when the active heating (as burning fuell) is involved.
For example a closed box with some air, fuell and an ignition system. Ignite the fuell the box heaths up then cools again with energy going out of the box. Weighing before and after after weighs lighter (by a miniscule fraction).

This is not from temperature raise the temperature goes as a wave for this just showing the process to the outside ; The reading (for themperature) increases then turns back to normal.
The meassurement with the most difference is for same temperature then before and after. Because the box keeps radiating heath to the environment. At it,s peak temperature the weight would be somewhere in between but keeps decreasing from ignition until reaching stable temperature.
Afterwards the difference in weight is as a memory for the event. Same as the temperature wave shows it simultaneous.
This case an energysource is left out of the system (thus equations) and I don,t know if theory predicts anything then. Maybe it just does with some interpretation.

6. I don't do relativistic stuff very often, but think drugstore math could become a factor. If the metal being heated is enveloped by air such that there is a bit of buoyancy, then the expanded volume of metal as it gets warmer would net a reduction of weight.

7. Originally Posted by dalemiller
I don't do relativistic stuff very often, but think drugstore math could become a factor. If the metal being heated is enveloped by air such that there is a bit of buoyancy, then the expanded volume of metal as it gets warmer would net a reduction of weight.
I did wonder myself if this question was about Archimedes' principle.

8. Weight reduction recorded in AIR is larger than expected from expansion and buoyancy. Glaser says heat convection (air currents around the sample) is responsible for most of the reduction in weight. An experiment weighing a heated metal in VACUUM should eliminate buoyant effects of expansion all together (Archimedes principle only applicable in fluids) and test if heat convection is the culprit for the reduction of weight.

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