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Can u change time on a watch by

  1. Oct 28, 2004 #1
    this is just a question, but according to physics, if you put a magent on each side of watch (the watch is like half an inch, normal wrist watch) and applied equal gravitational force on the watch in the middle, since the net gravity is zero, would the watch speed up/ slow down in time telling, as in an airplane the speed of a watch is different than on earth, so what would happen if the watch's net gravity was zero?
  2. jcsd
  3. Oct 28, 2004 #2


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    If the net gravity on a watch these zero, the watch will record time slightly faster than it does in an "Earth-normal" environment. However, this cannot be accomplished with magnets. Magnets can suspend a watch and keep it from falling, but setting the watch on a tabletop will do the same thing. Neither of these have any influence over the effect of gravity on the watch (nor will anything else, as far as we know).
  4. Oct 29, 2004 #3
    "If the net gravity on a watch these zero, the watch will record time slightly faster than it does in an "Earth-normal" environment"

    how much faster?
  5. Oct 29, 2004 #4


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    You're not affecting gravity when you stick a magnet onto a watch. Observe that when you release them, they still fall to the ground.

    The watch may run differently due to its internal electrical components operating differently under the influence of a stong magnetic field, but the result will have nothing whatsoever to do with gravity.

    You cannot cancel gravity. The only way to experience lower gravitational field strength is to get further away from the center of the earth. Climb a mountain, or build a rocket. That's about it.

    - Warren
  6. Oct 29, 2004 #5
    chroot- u didnt really answer my question, well u techinically did but that wasnt what I was asking. the left middle right object action is taking place, (the magnet, object, magnet) and the pull factor doesnt have to be magnets, but another object. but I was just saying, if you put a watch in the pull field, and it had a net gravity of zero, it would be suspended in air like Lurch said. so by how much time would the watch speed up like that? since he said "slightly faster" sorry for the confusing magnet demo.... it doesnt have to be magnets, but anything that has an equal pull factor
  7. Oct 29, 2004 #6


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    Magnets apply a magnetic force, not a (significant) gravitational force. You do not alter the gravity around the watch by suspending it between magnets. Why magnets...why not strings....or for that matter, the fact that it is strapped to your wrist should do...shouldn't it ?
  8. Oct 29, 2004 #7


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    I can't make head or tails out of this question as written, but I can answer a similar question that's interesting.

    Suppose one had access to hyperdense materials, far denser than normal matter. (Example: the science fiction story "The Singing Diamond" by Robert Forward, where the hyper-dense material is electron degenerate matter contained in a diamond matrix).

    Suppose one then supported a mass of such hyperdense materials on the surface of the earth, such that a point of "zero gravity" was created on the Earth's surface, due to the fact that the attraction to the Earth was exactly balanced by the attraction to the hyper-dense object at said point.

    Note that there aren't any magnets in this re-formulation of the question (I don't know what the magnets were doing in the original question), and that there are no magical "gravitational devices" in this re-formulation either.

    Suppose one then put a clock at the point where the gravity was cancelled out. Make it a very small clock (like a cesium atom) if you like, or extend the region of cancellation by making the hyper-dense object a disk - the details don't matter much, but I will do the calculation for a point mass, it's easier.

    Such a clock will run almost exactly at the same rate as a non-suspended clock. The reason for this is that time dilation is proportional to gravitational potential energy, not the gravitational field.


    Time Dilation Formula

    for a reference. This has also been discussed on the Physics Forum in the Relativity Forum a few times.

    Now all we need to do is to evaluate the total gravitational potential energy of the suspended clock to figure out the total time dilation. The potential energy a distance R away from a massive object M is

    E = -GmM/R = -(GmM/R^2)*R = -g*R

    where g is the acceleration of gravity.

    With two objects, we have to add together

    -g*R + -g*D

    where D is the distance that the clock is away from the hyper-dense mass that is cancelling out the Earth's gravity. Because it is cancelling out the Earth's gravity, 'g' is the same acceleration for the Earth and for the hyper-dense object. But because D << R, the total contribution to the gravitatonal potential energy of the hyper-dense mass will be small compared to that of the Earth.

    The gravitational time dilation at the Earth's surface is already very small (one part in 7*10^-10) to begin with (see the URL above for the calculation) - and the additional time dilation due to the hyper-dense object will be many times less than that of the Earth (by a factor of D/R).
  9. Oct 29, 2004 #8


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    If you use a magnet or anything else (like your wrist, as Gokul said) to suspend a watch in midair, its rate doesn't change at all from when it is sitting on the ground.

    Only gravity causes gravitational time dilation.
  10. Oct 30, 2004 #9
    well you guys are getting awfully technical on here, and I didnt want to take the time and write out the exact perfect wording, but thanks for the explenation and formula pervect
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