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Does weight / inertia / momentum change with temperature?

  1. Jul 6, 2015 #1
    I did a simple experiment. I took a small block of copper (40g) and sensitive scales. First I cooled the block in a freezer (-2C) and checked its weight. Then heated it up to 300C in the oven and checked weight again. The difference in weight is well observed (4 - 5mg). Results are consistent and repeatable. The only conclusion I can make from it (apart from the obvious that many formulas in physics don't work in the real world) is that inertia and momentum also get affected with heat.
  2. jcsd
  3. Jul 6, 2015 #2
    Can the effect be explained by buoyancy? Hotter -> thermal expansion -> displaces more air -> weighs less, but mass is unchanged.
  4. Jul 6, 2015 #3


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    Staff: Mentor

    Also, water vapor in the air tends to condense on cold objects. And heating an object that much probably drives off (evaporates) stuff that's condensed on the surface. Not just water, but also oils from fingerprints, etc.

    Was the object heavier when hot or when cold?
  5. Jul 6, 2015 #4
    Why speculate about this? Why don't you just calculate the effect and see what you obtain?

    I don't know the geometry of the experiment, but there may have been natural convection currents in the air (caused by the hot block) in proximity with the scale that could have affected the measurement. Also, how about just the effect of the higher temperature on the scale mechanism?

    I don't think that the mass of the block changed.

  6. Jul 6, 2015 #5
    I've done the calculation before. Students learn more if you encourage them to do it rather than posting the result. The OP also posted the magnitude of their observed effect, but not the direction. There is less motivation to chase down explanations when essential information is absent.
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