Magnets

[clusterm2]

Does a magnet do 'work' when moving something?...I guess it does, but where does the energy come from?

 

[James R]

Does a magnet do 'work' when moving something?...I guess it does, but where does the energy come from?

Can you give an example of the kind of thing you're talking about?

 

[Soapy Sam]

If something moves, work is done.*
(Which is nearly, but not quite, what someone just said to me.)







*In the context of the OP.
Pedants!

 

[Chris Haynes]

http://science.howstuffworks.com/electricity3.htm

Sometimes the energy to move that magnet comes from rivers:
http://people.howstuffworks.com/hydropower-plant.htm

or natural gas (which initially got its energy from the sun):
http://travel.howstuffworks.com/turbine1.htm

or nuclear reactions:
http://science.howstuffworks.com/nuclear-power.htm

Try it yourself with a magnet and some wire:
http://amasci.com/amateur/coilgen.html

 

[clusterm2]

I'm talking about a strong magnet supported say 8cm above a (wooden) bench, a piece of mild steel on the bench under the magnet but held by some simple mechanical means.
When the piece of mild steel is released it jumps up to the magnet so work has been done lifting an object.

Now can this be done say 1,000 times, 10,000 times or a 1,000,000 times surely this means the magnet has tremendous energy reserves..no?

 

[Leif Roar]

No.

The energy that lifts the steel up from the bench comes from the potential energy the piece of steel has in the magnetic field from the magnet, in the same way that the energy that sets a ball rolling down a hill comes from the potential energy the ball has in the gravitational field of the earth.

If you want to do this again, you will first need to pull the steel away from the magnet (which takes work,) much as you'll have to push the ball back up to the top of the hill if you want to send it rolling again.

 

[Tez]

This just gave me an interesting thought. If we had magnets with a curie temperature that was around room temperature, then we could extract energy this way from the natural temperature fluctuation between day and night - at night, while its cool, the magnet attracts the steel - then when the temperature increases the magnet goes through a phase transition and the steel drops etc etc... May not be that efficient, but it'd make a cool science demo.