# Decreasing strength of magnet by weights

1. Jul 9, 2014

### manp

Hi all

I've been trying to use weights, springs and elastic bands to basically decrease the bonding of a piece of metal and magnet. Basically what im trying to achieve is as the magnet attracts the metal i want the attraction to weighed down consistently, but im failing to do this as the items Im using are constant in strength and the magnetic field gets.stronger and stronger the closer it gets (havent figured out how to check strength over length). Os there any other way that i can increase the weighing down towards the end?

2. Jul 9, 2014

### Simon Bridge

If you apply a force to the metal that opposes the magnetic force, then the net force on the metal is reduced - but the force due to the magnet is not.

... do you mean that you want the net force on the metal to be a constant with distance from the magnet?

Note: you can get a profile for how the force due to the magnet on the metal varies with position by using a spring.

3. Jul 10, 2014

### manp

Yeh thats what I need, I would like to apply a force to the metal thats constant to the strength of attraction is there any way to do this?

4. Jul 10, 2014

### Simon Bridge

If you put a charge on the metal you could use an electric field to oppose the magnetic field.

5. Jul 10, 2014

### manp

I thought about that too and binding a magnet just under the metal piece but i want there to be an attractive force too so if i put a charge on it itl just be repulsion

Could buoyancy work in any way?

6. Jul 10, 2014

### Simon Bridge

Nonsense. Just use a weaker electric field.
The main advantage here is that you can, in principle, shape the electric field to provide the correct amount of balancing force for the magnet everywhere.

You would face the same problem as with the weights - the buoyancy force will be a constant but the magnetic force varies with position.

If you just want a constant "action at a distance" type force, then you can build uniform fields easily enough.

What are you trying to achieve?

7. Jul 10, 2014

### manp

time delayed action;4794155]Nonsense. Just use a weaker electric field.
The main advantage here is that you can, in principle, shape the electric field to provide the correct amount of balancing force for the magnet everywhere.

You would face the same problem as with the weights - the buoyancy force will be a constant but the magnetic force varies with position.

If you just want a constant "action at a distance" type force, then you can build uniform fields easily enough.

What are you trying to achieve?[/QUOTE]

Thanks again. Im trying to attract the piece withthe magnet so there is a directional movement, once the bonding has occured id like an opposing force ever so slightly less than the attraction so there is still bonding. The idea which you proposed is good but will there be a directional movement then the opposing force? I think what i ideally need is a time delayed action, is there anything you could reccommend mechanically?

8. Jul 10, 2014

### Simon Bridge

... yes but why? What is the purpose of doing this? What is the problem you are trying to solve or the end you are trying to achieve?

Of course!
You can make the electric field produce any force you like on the charged metal, at any position.
As long as the E-force is less than the B-force, the metal will accelerate in the direction of the (residual) B-force.

If you like, you can arrange for a strong E field close to the pole of the magnet where contact occurs so that the resulting E-force will be almost the same, but slightly less than, the B-force at contact.

You could also just switch the E-field on and off when you need it - put it on a timer if you like or put a switch on the magnet so when contact is made, the E-field switches on. In fact this is easier than trying to maintain a constant force.

For that matter - if you use electromagnets instead of permanent magnets, you can just switch them on and off as you will.

9. Jul 10, 2014

### manp

I just realised why i couldnt do the above method, i need to use a spherical magnet lol any other ideas? The task is part of my project in physics class

10. Jul 12, 2014

### Simon Bridge

Not without details.