On 1/31/07, Robin van Spaandonk <[EMAIL PROTECTED]> wrote:
In reply to John Berry's message of Sun, 28 Jan 2007 23:48:21 +1300: [snip] What about the reverse situation. The time it takes for the force from the bottom magnet to reach the top magnet? Wouldn't that produce the reverse effect? ...and what is supporting the top magnet...I think you need to look at the effect on *all* the forces involved before concluding that there is a net resultant uni-directional force.
I think you misunderstand. Both magnets are held in the attractive position at a fixed distance, glued to each side of a piece of wood if you like. Then we will apply an even constant acceleration force. (or we simply assume gravity is the same as acceleration, shouldn't magnetic fields be bent by gravity if light is?) Now at any moment the magnetic field around the magnet is renewing it's magnetic flux, that is to say if you turn a magnet by 90 degrees this new magnetic field doesn't instantaneously propagate, it takes time. In the same way if I have a magnet which is attracting another magnet, and then I remove this magnet the other magnet must not immediately be aware that the other magnet has been withdrawn (turned off) so it still feels the same force for a period of time. Much the same is happening here, while the magnets are being accelerated together, when the magnetic flux from the bottom magnet gets to the top magnet it doesn't know that the position of the magnet that created it has now changed and has kept pace with the top magnet so it has a weaker field or a field that doesn't extend as far in front of it, so the top magnet is not as much attracted down. However the reverse is true for the field from the top magnet, it can't know the magnet has receded and so it has a more powerful effect of attracting the bottom magnet up the page than it should. This leads to a net force up the page in the direction of acceleration, or against gravity. In repulsion the force would be reversed.
