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Obviously gravity pulls objects towards the earth's surface. Now suppose I have a refrigerator and a magnet. The magnetic force is perpendicular to the gravitational force. So it is not counteracting it. So why does the magnet not get pulled to the ground since no other force is opposing it?

My instinct is that the magnetic force pulls the magnet closer to the refrigerators surface and this increases the friction. as a result the magnet does not fall to the floor. But I'm not sure this is correct.

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As you may know, the friction is proportional to the normal force of an object or in this case the force of attraction between magnet and refrigerator. If your force is strong enough then the friction will be sufficient and the magnet will not slip (on earth the force of friction must exceed the mass of your magnet multiplied by 9.81 m/s).

If we assume your magnet weighs 0.010kg and is made of iron, while your refrigerator is steel then the coefficient of friction is 0.4 (Engineering Toolbox, Friction and Coefficients of Friction). The force exerted by the magnet on the steel is 5N.

Friction = 5 x 0.4 = 2N

Now we find that the Force down is equal to 0.010 x 9.81 ~ 0.1N

The magnet would stick

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  • $\begingroup$ Presumably, you are talking about static friction... right? $\endgroup$ – Solomon Slow Apr 21 '15 at 17:29
  • $\begingroup$ Thats right if the magnet was sliding the friction would be lower $\endgroup$ – Jaywalker Apr 21 '15 at 17:33
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f(friction) directly proportional to N(normal force acting, perpendicular to the plane of fridge in outward direction here) is the force that opposes motion, now friction will in this case be provided by the atomic attraction, only atomic attraction is taken into account here, because repulsion would not even let it attach to refrigerator, after the force is removed. Hence here are cases that can hold:

Friction equals or outweighs your magnet, the magnet won't move(your case).

Friction less than weight of magnet, magnet moves downwards or towards the Gravitational pull.

Thanks:)

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