Gravitation vs Magnetic and Electric Field

  1. There is a Magnetic and Electric Field around every planet and the sun due to the dipole action they produce. They vary with a factor of r^-3. Are these forces the stuff that gives gravitational forces its name or is there more to it?
     
  2. jcsd
  3. D H

    Staff: Mentor

    Gravity results from mass, not charge, and varies with a factor 1/r2, not 1/r3. The Moon and Mars have almost no magnetic field but still have a gravitational field.
     
  4. Worse: the Sun's magnetic field does not decrease as r^-3. This has long been a puzzle. A common explanation now is that flux gets entrapped in Solar wind and transported away with a smaller decrease.
     
  5. Magnetic forces are strong enough to influence the elliptical nature of the orbit though.
     
  6. D H

    Staff: Mentor

    The orbit of what? Neither JPL (DE40x series of ephemerides) nor the St. Petersburg Institute of Applied Astronomy's (EPM200x series ephemerides) model electromagnetic interactions amongst the sun and planets.
     
  7. Then there are many fields that effect our Universe. One, gravitational field. Two, Magnetic and Electric, and then "Dark Energy" which we won't go into now. The Magnetic and Electric Fields are "out" as a cause for the elliptical orbit of the planets. What is the cause of the elliptical orbit of the planets around the sun?
     
    Last edited: Nov 11, 2008
  8. D H

    Staff: Mentor

    Gravity.
     
  9. I know now gravity is much much greater of a force than Magnetic and Electric Field. I heard that the Sun flips its Magnetic Field during the course of a year. Does that disrupt things?
     
  10. D H

    Staff: Mentor

    Actually, gravity is by far the weakest of the four fundamental interactions. Two protons, for example, will fly away from one another because the electrostatic repulsive force between a pair of protons is more than 1036 times stronger than the gravitational attractive force between a pair of protons. Electromagnetism in turn is much, much weaker than the strong force at short distances. Think about it this way: the strong force is powerful enough to hold protons together at extremely short distances.

    We don't have to account for the strong force at anything but subatomic levels because the particles that mediate the strong force aren't stable; the strong force simply dies out. The electrostatic force similarly dies out at largish distances because most reasonable sized conglomerations of matter are electrically neutral. The only thing that is left on planetary scale and larger are the gravitational force and multipole electromagnetic forces (e.g., Earth's electromagnetic field).

    The multipole electromagnetic fields are pretty dang weak. Think about it this way: Watch a compass needle. It doesn't snap into alignment with the Earth's magnetic field. It slowly meanders into alignment. The Earth's magnetic field averages 0.5 gauss on the Earth's surface. In comparison, the field of a small bar magnet at the boundaries of the magnet is about 100 gauss. It gets worse than that: the multipole fields drop as the inverse cube of distance. On planetary scales and larger, the gravitational force completely predominates the other fundamental interactions.
     
  11. but at Wilczek once put it, this is really because, measured in natural units, the protons' masses are extremely tiny (compared to the Planck mass) while the protons' charge are just a single order of magnitude away from the Planck charge. that's how i would compare apples-to-apples.

    i think this illustrates why, on the grand scale, there is only gravity left in the contest of forces of orbits and such. unlike E&M, for gravity like-signed "charges" attract, there seems to be only positive masses around doing celestial mechanics. even though, if you were measuring things in kg and coulombs, the E&M force is so much stronger than gravity, celestial bodies are pretty much neutral in electric charge. the superposition of what the charged particles do to each other in the stars and planets pretty much cancel out because of the equal numbers of protons and electrons in them. though there aren't net EM forces between them, but since we're all positive mass, there is gravity left.
     
  12. So... does it mean that it makes no difference for earth's magnetic field if gravity is decreasing? Is it staying the same or will it disapear?

    what is exact relationship between gravity and magnetic field?
     
  13. The magnetic field is caused by an electric current doing loops somewhere inside the Earth.

    Gravity depends on the mass of Earth.

    If you can understand what mechanism causes the two different phenomenon it becomes apparent that the two dont directly affect each other. Mass and gravity of an object is not involved anywhere in the equations that describe magnetic force and field, you see that decreasing mass/gravity wont affect magnetism in any direct way.

    This isn't to say that there is no indirect relationship. It is easy to imagine that decreasing the mass/gravity could possibly affect the amount of current or size the path that the current inside the earth is traveling. This would, in turn, affect the mag field.
     
  14. I thought so, but i wasn't sure. It's all because Earth's magnetic filed is not fully explained yet. I'm not studying physics so had small problem. Thx anyway. Sorry if you found my question stupid ;D lol
     
  15. A good explanation on how does gravity cause the elliptical orbits around the sun.
    [crackpot link deleted]
     
    Last edited by a moderator: Nov 18, 2008
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