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Super compass

  1. Oct 18, 2005 #1
    for a normal compass, when you change the direction, the needle will rotate itself to line up wiht the north and south line, but the rotation is very slow. do we have some kind compass which its needle rotates very quickly, that seems not moving respect to the north-south pole...? I mean the compass have a very strong magnetic attracion itself...
    sorry, my english is not that good....:tongue:
  2. jcsd
  3. Oct 19, 2005 #2


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    Modern navigational compasses hold a magnetized needle inside a fluid-filled capsule. The fluid is inejcted in so it causes the needle to stop quickly, instead of waving around the general direction. Its the fluid that is making it slow, put in on purpose, so the compass is easy to read.

    If there was no fluid it would shake around a lot before it stopped, and pointed north/south. Just like if you tie a ball to a long piece of string, hold the ball up, and let go. The ball will swing back and forth for a while before stopping in the middle. You will find if you do the pendulum experiment underwater, the ball will stop much more quickly.

    If you want a "supercompass," you can take the needle out of your compass, tie a string around the middle and hold it up. Air is easier to move through, it will spin to north/south very quickly.

    Compasses were initially used in geomancy in ancient China. The first known use of Earth's magnetic field in this way occurred in ancient China as a spectacle. Arrows were cast similarly to dice. These magnetised arrows aligned themselves pointing north, impressing the audience. There were also "magic spoons," when thrown on the ground they always pointed the same way.

    "Dream Pool Essays" written by Song Dynasty scholar Shen Kua in 1086 AD showed how he made a compass. Shen Kua started by rubbing its tip with lodestone, and hanged the magnetic needle with one single strain of silk with a bit of wax attached to the center of the needle. He said it always points either north or south.
    Last edited: Oct 19, 2005
  4. Oct 20, 2005 #3
    thanks for the information.
    I wonder if there is somekind compass make of neodymium. Neodymium has a very strong magnetic attraction, much stronger than the normal one. if i use it to make a coordinate system, will that be stable enough...
  5. Oct 20, 2005 #4


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    Staff: Mentor

    Actually, most compasses used for navigation are not magnetic, they are gyroscopic. The gyroscope is aligned with the true north pole (which makes calculating headings easier than using magnetic headings) and since it's alignment doesn't change, the readout of the correct heading is instantaneous.
  6. Oct 20, 2005 #5


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    Staff Emeritus
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    Neodymium (Nd) itself is not magnetic. You probably mean NdFeB, which is a high-strength permanent magnet. As Mk explained though, it's not merely the strength of the magnetic needle that matters, but damping forces as well. Actually increasing the magnetization could help some, in that it would reduce the amplitude of the response to perturbations.

    But why do you care ? What appplication needs this quick response time from a compass ? Why not just use a GPS device or gyroscope ?
  7. Oct 27, 2005 #6
    actually, i need to need a constant coordinates system for a project, and that is my idea,,,,
    i wonder if this design work...

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