6 ms·

The mass of a chunk of atoms depends on their temperature and their purity, which are things you can't measure very accurately the more atoms you have. Essenti

by Retra 11y ago

The mass of a chunk of atoms depends on their temperature and their purity, which are things you can't measure very accurately the more atoms you have. Essentially, that's what they were doing with Le Grande K. It's unstable because molecular properties are unstable in aggregate.

tomp 11y ago
The second depends on a specific isotope at a specific temperature, 0K, so it's all theoretical anyways. How you define something doesn't need to coincide with how you measure it.
- Retra 11y ago
  It's far easier to measure a single isotope at a specific temperature limit than it is a whole rod of them. Just because they're both theoretical doesn't mean there isn't a huge practicality component to the decision.
sklogic 11y ago
How exactly mass depends on a temperature?
- Retra 11y ago
  Measured mass is a function of total energy.
  - sklogic 11y ago
    It is not a mass (or a "rest" mass, if you want to use this incorrect and unnecessary notion) that you measure.
- IvyMike 11y ago
  E=mc^2 You may be thinking "Oh, you fool--E=mc^2 is for fission and fusion, and certainly doesn't apply to things like the energy in the heat of an object". But weirdly, it does. https://physics.stackexchange.com/questions/87259/does-decrease-in-temperature-affect-mass-e-mc2 https://physics.stackexchange.com/questions/87259/does-decre...
  - Pyxl101 11y ago
    It also applies to things like gravitational potential energy, or velocity. Climb a flight of stairs, and you gain energy. Gaining potential energy really means that you've gained mass, and so you're heavier at the top of the stairs than at the bottom. The amount that you are heavier depends on the amount of energy you gained, converted into mass. Similarly, as you gain velocity, you gain kinetic energy, which also makes you heavier. If you wave your hand in front of your face, your hand's motion causes it to gain mass. Velocity also dilates time, so time passes ever so slightly slower than for the rest of your body. This typically only matters in a relativistic context, and doesn't impact day to day life. The difference in passage of time can be measured by an atomic clock if you put it on a rocket into space, but is otherwise insignificant. It's unlikely any scale could measure your weight-gain from climbing stairs, since the amount of energy you gain is insignificant when converted into mass. You can compute the mass gain by solving for "m" in the formula E=m*c^2, so m=E/(c^2). The speed of light c is a really big number, and so to compute the mass you gain, you're dividing the energy by c^2, which is a much bigger number. Thus a gain to kinetic or potential energy does not noticeably affect your mass in day to day situations. Conversely, if you can convert any meaningful part of your mass into energy, then it's an absolutely tremendous amount of energy: atomic weapons.
    - tomp 11y ago
      > Gaining potential energy really means that you've gained mass I've never heard this before. Can you link to some further explanation? Intuitively, if anything, you'd lose mass, because you're in a place now where space is less curved than where you were before.
      - marcosdumay 11y ago
        The system composed of you + planet gains mass. You can not measure a different rest mass for yourself at either situation, so you'll probably attribute the extra mass to the planet (and the planet to you). And yes, there's also some change due to changes in gravity. I'd expect that to be much smaller. But IANAP, and not that good with relativity.
  - 11y ago

by Retra 11y ago

tomp 11y ago

The second depends on a specific isotope at a specific temperature, 0K, so it's all theoretical anyways. How you define something doesn't need to coincide with how you measure it.

Retra 11y ago
It's far easier to measure a single isotope at a specific temperature limit than it is a whole rod of them. Just because they're both theoretical doesn't mean there isn't a huge practicality component to the decision.

sklogic 11y ago

How exactly mass depends on a temperature?

Retra 11y ago
Measured mass is a function of total energy.
- sklogic 11y ago
  It is not a mass (or a "rest" mass, if you want to use this incorrect and unnecessary notion) that you measure.
IvyMike 11y ago
E=mc^2 You may be thinking "Oh, you fool--E=mc^2 is for fission and fusion, and certainly doesn't apply to things like the energy in the heat of an object". But weirdly, it does. https://physics.stackexchange.com/questions/87259/does-decrease-in-temperature-affect-mass-e-mc2 https://physics.stackexchange.com/questions/87259/does-decre...
- Pyxl101 11y ago
  It also applies to things like gravitational potential energy, or velocity. Climb a flight of stairs, and you gain energy. Gaining potential energy really means that you've gained mass, and so you're heavier at the top of the stairs than at the bottom. The amount that you are heavier depends on the amount of energy you gained, converted into mass. Similarly, as you gain velocity, you gain kinetic energy, which also makes you heavier. If you wave your hand in front of your face, your hand's motion causes it to gain mass. Velocity also dilates time, so time passes ever so slightly slower than for the rest of your body. This typically only matters in a relativistic context, and doesn't impact day to day life. The difference in passage of time can be measured by an atomic clock if you put it on a rocket into space, but is otherwise insignificant. It's unlikely any scale could measure your weight-gain from climbing stairs, since the amount of energy you gain is insignificant when converted into mass. You can compute the mass gain by solving for "m" in the formula E=m*c^2, so m=E/(c^2). The speed of light c is a really big number, and so to compute the mass you gain, you're dividing the energy by c^2, which is a much bigger number. Thus a gain to kinetic or potential energy does not noticeably affect your mass in day to day situations. Conversely, if you can convert any meaningful part of your mass into energy, then it's an absolutely tremendous amount of energy: atomic weapons.
  - tomp 11y ago
    > Gaining potential energy really means that you've gained mass I've never heard this before. Can you link to some further explanation? Intuitively, if anything, you'd lose mass, because you're in a place now where space is less curved than where you were before.
    - marcosdumay 11y ago
      The system composed of you + planet gains mass. You can not measure a different rest mass for yourself at either situation, so you'll probably attribute the extra mass to the planet (and the planet to you). And yes, there's also some change due to changes in gravity. I'd expect that to be much smaller. But IANAP, and not that good with relativity.
- 11y ago