Force exerted by a magnet

[Zolar V]

Hey fellas,

I know its been a freaking long while since i posted or visited here last.

But i was remembering an old experiment i did back in high school that i couldn't do right. I know that the data i was supposed to see was going to be a positive exponential increase. But my data was too jittery, mostly due to poor experiment setup and execution.

 

Ok, this is what i was trying to find:

If you have 2 permanent magnets ( i used 2 Neodymium barrel type magnets. 1 In Dia, 2 In height) How much force is one magnet being pushed away from the second magnet.

 

My hypothesis: As the second magnet gets closer, the first magnet will be pushing away harder. Scaling exponentially, until there is no more space left between the two magnets. As distance between the two magnets decreases the force exerted by the first magnet to move away from the second one increases.

 

 

My experiment design wasn't all that great as i had to basically jerryrig all of the devices together for unintended purposes.

I used a grooved aluminum yardstick, (grove fit magnets pretty well and easily slid) and there was this electronic force scale that im pretty sure i had to turn on its side and attach to one end of the yard stick. Though, after calibrating, the only real issue was that i used my hand to slowly move the second magnet close. Several attempts were thwarted by jittery hand movements, and some were thwarted by the one magnet being pushed up instead of back.

I set one magnet on the rail with the backside touching the force scale, while i placed the other magnet on the rail away from the first. i grasped the second magnet and slid it closer to the 1st.

+ = magnet

- = Rail

[ = force scale

 

[+------------+

i moved the second magnet closer:

 

[+----+

and so on.

 

Also note, i used like sides as to repel one another.

 

 

SO: now on to you guys. IF you would be so kind as to gather the data i was looking for. I don't have any of the equipment necessary, nor the magents either. I would really like it if you would also test several different sizes of magnets too. E.G:

1cm Diameter, 2cm long: 3cm diameter, 4cm long: 5cm diameter, 5cm long:

2cm diameter, 4cm long: 4cm diameter, 5cm long: 6cm diameter, 6cm long:

3cm diameter, 6cm long: 5cm diameter, 6cm long: 7cm diameter, 7cm long:

[Schrödinger's hat]

My first thought if budget is limited would be to use string and gravity for something like this.

 

Tie the magnets to strings in different places, then adjust the length so that they almost, but can't quite touch. With a bit of fiddling you should be able to get them to sit in equilibrium.

Then measure the distance between and the angle.

Use your knowledge of forces (or ask if you don't know much about forces) and a measurement of the weight to work out their force on each other.

 

It may be easier if you use one fixed magnet and one string, then move the other end up as well as away.

Or maybe one very short string (so the magnet always faces the correct direction) and one long string.

Experiment a bit

If you have trouble with strings, it can be easier to manage a stiff rod, but it's harder to work out the forces in this case (because the rod has significant weight).

 

As to your exponentially increasing force hypothesis. Why did you pick exponential? Can you think of any other types of function that increase as r approaches 0?

Maybe try more than one?

If you can find other functions you could compare them to an exponential. See what fits best.

[Zolar V]

My first thought if budget is limited would be to use string and gravity for something like this.

 

Tie the magnets to strings in different places, then adjust the length so that they almost, but can't quite touch. With a bit of fiddling you should be able to get them to sit in equilibrium.

Then measure the distance between and the angle.

Use your knowledge of forces (or ask if you don't know much about forces) and a measurement of the weight to work out their force on each other.

 

It may be easier if you use one fixed magnet and one string, then move the other end up as well as away.

Or maybe one very short string (so the magnet always faces the correct direction) and one long string.

Experiment a bit

If you have trouble with strings, it can be easier to manage a stiff rod, but it's harder to work out the forces in this case (because the rod has significant weight).

 

As to your exponentially increasing force hypothesis. Why did you pick exponential? Can you think of any other types of function that increase as r approaches 0?

Maybe try more than one?

If you can find other functions you could compare them to an exponential. See what fits best.

 

Like i said, i don't have the equipment anymore. Right now performing the experiment by myself just isn't feasible.

 

I picked exponential (in my initial hypothesis), Subsequently the data i collected even though it was jittery still supported this hypothesis.

[Moontanman]

The aluminum could be a source of instability since it is dia-magnetic, the idea of the strings is a good one, you could glue the strings to the end of the magnet with super glue maybe?

[Schrödinger's hat]

Like i said, i don't have the equipment anymore. Right now performing the experiment by myself just isn't feasible.

 

Neodymium magnets are a few dollars each on ebay.

On top of that you'll need string, maybe some super glue (if you can't find a magnet with a hole in the middle) and I've seen electronic kitchen scales that go down to 0.1 grams -- maybe ask your neighbours/friends if you can borrow theirs?

[Zolar V]

i don't seem to be able to stress this enough, I cant do it.

 

it is a simple experiment, and im sure that the people who read this forum are likely to have access to/ or the supplies to accomplish it.

[Tres Juicy]

i don't seem to be able to stress this enough, I cant do it.

 

it is a simple experiment, and im sure that the people who read this forum are likely to have access to/ or the supplies to accomplish it.

 

 

You cant expect people to do your dirty work for you

 

I suppose you'll just have to remain frustrated and curious....

[swansont]

You cant expect people to do your dirty work for you

 

I suppose you'll just have to remain frustrated and curious....

 

Oh, I don't know. I just bought some magnets, and might be able to find time to mock up an experiment.

[John Cuthber]

Someone already did it.

http://en.wikipedia.org/wiki/Magnetic_moment#Forces_between_two_magnetic_dipoles

though I have to admit I'm struggling to understand the outcome.

[Tres Juicy]

Oh, I don't know. I just bought some magnets, and might be able to find time to mock up an experiment.

 

 

Haha post the results (I'm secretly dying to know...)

[swansont]

I couldn't keep the magnets from flipping and attracting. I need a more sophisticated apparatus than a few magnets, a plastic cup, a scale and a ruler.

[Tres Juicy]

I couldn't keep the magnets from flipping and attracting. I need a more sophisticated apparatus than a few magnets, a plastic cup, a scale and a ruler.

 

Yes, magnets are a nightmare to work with.

 

I bought some VERY stong neodymium magnet a few months ago to expiriment with. They would frequently jump together with such force that they would catch bits of my skin between them and split it (I took to calling them "magnet bites"), if I was lucky enough to get out of the way they would either shatter or become very difficult to get them apart again.

 

I got one of my friends to put one either side of his ear lobe for fun, it took him about 20 minutes of sreaming to get them off

[Schrödinger's hat]

I couldn't keep the magnets from flipping and attracting. I need a more sophisticated apparatus than a few magnets, a plastic cup, a scale and a ruler.

 

Perhaps you could glue/tape one to something heavy/wide?

[CaptainPanic]

When I did such experiments (I really don't understand why Zolar can't buy 2 magnets for like 1 euro in total), I had 2 short bar-magnets. I put tape around them until they could be jammed into a straw (the ones you get for free at McD's). You want the "string" you hang the magnet from to be straight anyway, so something more firm (but still lightweight compared to the magnet) is good enough. Then the flexible joit at the top was done with a regular string.

 

If you, like swantont seems to suggest, wish to calculate the exact force, you should indeed also include some scales to account for the attraction of the magnet which is on the bottom. Kitchen scales will quadruple the costs of the experiment to a staggering 10 euro.

 

What I enjoyed the most is if you suspend a magnet, and you place a bunch of magnets on the ground... the hanging magnet will be a pendulum, but will behave quite chaotic. And although

is a nice-looking setup, this can be built at home with very basic stuff.

[swansont]

Perhaps you could glue/tape one to something heavy/wide?

 

The magnets I was using are kinda strong (and they chipped when snapping together) — so I don't think they'd find tape to be much of an impediment, and the scale is limited to 1kg. I'll have to try it with some wimpier magnets.

 

————

 

The new Excel has changed everything, so I don't have labels. Y axis is the indicated mass in grams, X axis is distance in cm. Pretty big error bars would exist.

 

 

(Actual Y data: 46, 13, 4.2, 1.3, 0.6, 0.1)

[Zolar V]

Ahh, i remember this experiment and post!  Forgive my inability to accomplish the experiment in question, I was preoccupied with serving in the air force.  I picked an exponential function because at a 0 distance there would be a near maximum repelling force exerted, and at some distance (r) there would be a slight or nil force exerted.  After (r) the rest of the distances would also have a very small force, whereas  between 0 and (r) the forces would get a good bit stronger.

[studiot]

1 hour ago, Zolar V said:

Ahh, i remember this experiment and post!

 

And killed off several members in the process it seems.

What fate do you offer newcomers?

[martillo]

I think this experiment by Paul Doherty well determine the force between magnets showing exponential four in distance:

"Force between two magnets as a function of distance"