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Q & A: Use the Forces: Magnets and Gravity

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Most recent answer: 02/18/2013
Q:
Hello, I have a question on gravity and magnetism.Are they both the same kind of force i.e magnetic?If so why does gravity seem to attract all objectswithin its field including non - ferrous objects like you and me, yet normal magnets canít achieve the same?
- raburu (age 15)
Halifax Canada
A:
Gravity and magnetic forces are actually not the same type of forces, as far as we know. So far, scientists have found four types of forces - gravitational, electromagnetic (includes your magnets), strong nuclear, and weak nuclear. Strong and weak nuclear have to do with holding atoms together, and donít really relate to this problem. The force of gravity is exerted by (caused by) anything that has mass on anything else with mass. You and I actually have some gravitational force and attract everything else to ourselves - the earth, the computer, atoms, books - everything with mass. Fortunately, the force provided is related to the mass, so we only provide a small force. Planets, suns, moons, and things like that provide noticeable gravity that works on everything with mass - the earthís gravity holds the moon in place, and keeps us here, or brings back a ball if you throw it into the air. Electromagnetic force has to do with moving charges. You probably have noticed that most simple magnets have different colors - one color on each half. The colors mark the poles of the magnet - one end of the magnet is called "north" and the other "south". The north (south) side will attract the south (north) side of another magnet, or things that are susceptible to magnetism, like iron. Something else thatís kind of cool - the electromagnetic force is stronger than the gravitational force - this is why you can lift a nail with a magnet. Hope this helps! -Sara

(published on 10/22/2007)

Follow-Up #1: conservation of magnet energy

Q:
the law of conservation of energy says you can't get more energy out of a process than what you put in. think about a magnet stuck on the bottom of something...it has to take energy to hold it up against the force of gravity, but where is the magnet getting it's energy? will it eventually run out and fall? where does the conservation law come into play with this?
- richard servatius (age 64)
murray
A:
It doesn't take any energy for the magnet to stay stuck. Look at the height of the magnet. It's not changing. Neither are its mass nor the earth's mass. So the gravitational energy isn't changing. The distance from the magnet to what it's stuck on isn't changing, so the magnetic energy isn't changing either. This is the simplest type of conservation, where none of the components of the energy change. In more complicated cases one might go up while another goes down.

Mike W.

(published on 02/17/2013)

Follow-Up #2: When is work done?

Q:
If it is true that no energy is required to hold the magnet up; then why does it take energy to hold my arm level? It certainly gets tired, not moving, distances not changing, no acceleration. Isn't gravity affecting it? A non-magnetic material would normally fall in the same position, so something is holding it up - magnetism. Then doesn't magnetism use energy to do so?
- Richard Servatius (age 64)
Murray
A:

We've addressed this very question here:
http://van.physics.illinois.edu/qa/listing.php?id=20305.

Mike W.


(published on 02/18/2013)

Follow-up on this answer.