Magnet on metall wall

1. Oct 23, 2012

Crazymechanic

Hi

a simple question that struck my mind.Let's imagine a ferrite magnet from a old loudspeaker now let's put that magnet on a metal wall , or door , the magnet holds to the metal vertically and any other material put similar would just fall off so t seems to me that the magnet or the magnetic field is doing work.
So is this true that the magnetic field is doing work or is it wrong , is the magnet just arranging elementary particles in such a way that lets those two physical objects attract each other like opposite charges attract one another?

Tahnks.

2. Oct 23, 2012

tiny-tim

Hi Crazymechanic!

If I hang my hat on a peg on the wall, the peg stops the hat falling, but the peg does no work.

3. Oct 23, 2012

Staff: Mentor

Work = force * distance

Where's the distance?

4. Oct 24, 2012

Crazymechanic

Hmm interesting answers.Ok Russ I let's assume we have a 5cm thick magnet and 5cm thick metal door, let's put a 1cm thick plastic material between the metal door and the magnet is now the magnet doing work? because the magnet is still holding on but at a distance away..?

5. Oct 24, 2012

Staff: Mentor

No: That's force applied at a distance, not through a distance. The "distance" in the work equation is the distance the object moved.

6. Oct 24, 2012

CWatters

"through a distance" aka "displacement".

Compare a fridge magnet to a book shelf. Neither is moving (zero displacement). Neither is doing any work to hold itself up. Neither needs a power source.

7. Oct 24, 2012

CWatters

This is a very important concept in physics...

If you hold a heavy book out at arms length (constant height) your body is doing no work on the book because the book is not moving. It doesn't feel like that because of the way the body works - it's is a biological machine. Were it a machine made of say metal or wood no power would be required to hold it still at a constant height (such a machine is called a bookshelf).

Large numbers of people missunderstand this issue. As a result they think magnets are a potential source of energy and try to build perpetual motion machines from them. They are wrong.

8. Oct 24, 2012

AJ Bentley

Or Gyroscopes.
Gyros are very popular with the loony fringe.
Gyros AND magnets now... :D