# Magnet Force Help

1. Dec 19, 2006

### rukidding

Can anyone help me determine how much force is created when a one tesla permanent magnet is allowed to make contact with a flat piece of iron. The distance that this size magnet can be released and will be drawn to the iron is about 3 centimeters. Is there any way to express this force in joules or watts?

2. Dec 19, 2006

### Gokul43201

Staff Emeritus
There's not enough info to do a calculation, but a typical 1T magnet that's about the size of a quarter, will stick to a flat piece of iron with a force of about 20lbs (about 100N). You can't express a force in units of joules or watts (those are units for energy and power). You can, however, calculate the potential energy of the magnet-iron system, and that will be a number in units of joules.

3. Dec 19, 2006

### rukidding

What other info is needed? Here's what is listed on this magnet:

http://www.kjmagnetics.com/proddetail.asp?prod=DY0X0

Pull Force: 231.55 lbs
Surface Field: 7100 Gauss
Brmax: 13,200 Gauss
BHmax: 42 MGOe

With the above magnet,

if 20 lbs. equals 100 newtons

then,

231 lbs. equals 1155 newtons.

Is this correct?

When I go to online unit converters, I find that 1 watt = 1 joule = 1 newton.

I realize these are different terms relating to different things; power, energy and force. But is this how you would calculate the potential energy?

4. Dec 19, 2006

### Staff: Mentor

:surprised

Which converters give you that, so we can steer people away from them in the future? :grumpy:

5. Dec 19, 2006

### rukidding

6. Dec 19, 2006

### Gokul43201

Staff Emeritus
Woah! That's a big one!

Well, isn't this the information you are looking for?

Close, but a little high! To convert lbs to Newtons(N), multiply by 9.8/2.2 (or about 4.45).

This is completely nonsensical. What's true is that 1 Watt-second = 1 Joule = 1 Newton-meter. But this doesn't mean you can convert a force into an energy!

No, it's not. Any real calculation of PE will be far more involved.

Last edited: Dec 19, 2006