3 ms·

If you are really close to one pole of a magnet and far away from the other then the force scales like 1/r^2, it is in the far field under the influence of both

If you are really close to one pole of a magnet and far away from the other then the force scales like 1/r^2, it is in the far field under the influence of both poles of the magnet that it scales like 1/r^3. Electrostatics scales like 1/r^2 (because you fet isolated charges). The other two are a complicated story.

dotancohen 3y ago
If you have time, I would love to hear that complicated story. I remember once hearing that the rate of those forces' decay indicates (but does not prove) that they decay in more than three dimensions. This was an accomplished chemist talking, so I'm sure that she was being concise but factual.
- salty_biscuits 3y ago
  I might not be able to give a super coherent picture but I will have a go. The force that hold nuclei together is based on the residual strong force, it is a complex system so the models used for it tend to be semi-empirical (yukawa or reid potential). They go from being repulsive at short distances to being attractive with something like an exponential decay as you go further away. The force is very strong at 1 femtometre and pretty much negligible 3 femtometres away. This is only the residual of the strong force though, which is what you can think of as holding quarks together. This force is very strange in that it doesn't get weaker the further the quarks get apart, but if it gets far enough then the energy will create new particles. That's just the strong force, I will leave it to someone more knowledgeable than me to try to explain the weak force.
- malaya_zemlya 3y ago
  weak and strong forces are mediated by particles that have mass and therefore their force falls off basically exponentially, as exp(-m*r) it's not really the same as decaying in extra dimensions, because in that case the force law would look something like 1/r^(n-1)
- gus_massa 3y ago
  For a point or ball, the formula is F=A/r^2 For a complicated shape, the formula is (something like[1]) F=A/r^2+B/r^3+C/r^4+... , where r is the distance to the "center" (and some parts are closer and some parts are more far away). An important property of magnets is that A=0, so the r^2 term dissapears. And in many cases it can be simplified to F=B/r^3 [1, again]. [1] The complete formula considers also the directions, so it's longer https://en.wikipedia.org/wiki/Multipole_expansion https://en.wikipedia.org/wiki/Multipole_expansion

dotancohen 3y ago

If you have time, I would love to hear that complicated story. I remember once hearing that the rate of those forces' decay indicates (but does not prove) that they decay in more than three dimensions. This was an accomplished chemist talking, so I'm sure that she was being concise but factual.

salty_biscuits 3y ago
I might not be able to give a super coherent picture but I will have a go. The force that hold nuclei together is based on the residual strong force, it is a complex system so the models used for it tend to be semi-empirical (yukawa or reid potential). They go from being repulsive at short distances to being attractive with something like an exponential decay as you go further away. The force is very strong at 1 femtometre and pretty much negligible 3 femtometres away. This is only the residual of the strong force though, which is what you can think of as holding quarks together. This force is very strange in that it doesn't get weaker the further the quarks get apart, but if it gets far enough then the energy will create new particles. That's just the strong force, I will leave it to someone more knowledgeable than me to try to explain the weak force.
malaya_zemlya 3y ago
weak and strong forces are mediated by particles that have mass and therefore their force falls off basically exponentially, as exp(-m*r) it's not really the same as decaying in extra dimensions, because in that case the force law would look something like 1/r^(n-1)
gus_massa 3y ago
For a point or ball, the formula is F=A/r^2 For a complicated shape, the formula is (something like[1]) F=A/r^2+B/r^3+C/r^4+... , where r is the distance to the "center" (and some parts are closer and some parts are more far away). An important property of magnets is that A=0, so the r^2 term dissapears. And in many cases it can be simplified to F=B/r^3 [1, again]. [1] The complete formula considers also the directions, so it's longer https://en.wikipedia.org/wiki/Multipole_expansion https://en.wikipedia.org/wiki/Multipole_expansion