Magnet Force: Calculate Force from 1T Magnet & Iron

[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?

 

[Gokul43201]

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.

 

[rukidding]

There's not enough info to do a calculation,

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

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).

With the above magnet,

if 20 lbs. equals 100 Newtons

then,

231 lbs. equals 1155 Newtons.

Is this correct?

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.

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?

 

[jtbell]

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

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

 

[rukidding]

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

They clearly state that Newtons are per meter and watts are per second, but there seems to be a clear relationship.

http://www.onlineconversion.com/energy.htm

http://www.sciencelab.com/data/conversion_calculators/energy-conversion.shtml

http://www.translatorscafe.com/cafe/units-converter/energy/

 

[Gokul43201]

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

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

Woah! That's a big one!

Pull Force: 231.55 lbs

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

With the above magnet,

if 20 lbs. equals 100 Newtons

then,

231 lbs. equals 1155 Newtons.

Is this correct?

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

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

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!

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

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