# Can this work ?

1. Feb 3, 2008

### hitspace

A friend of mine . kind of savant genius ,but this time he has gone too far . hes got this wacko idea . hes all set to try and patent . im trying to help him out by getting some "real" physicists to tell him hes got his head on backward

heres what he thinks that if someone were to have a wooden box insulated on the outside with rubber . inside this box he will glue a very strong magnet to the bottom of this box . and on the top he will glue /weld a peg he will have a magnet travel up and down on this peg . he believes the repulsing force will force the magnet on top to push up against the box . he believes that a varying magnetic field namely a neodmyium magnet being the base magnet will cause the effect of levitation

he explained this by saying the upward repulsing force of a neodmyium magnet (say 100 pounds) is stronger than the other magnets 1 or 2 pounds of force as well as the force of gravity .

he assumes that magnetic fields repulsing is the effect of charged particles trying to push the
opposite magnetic field out of its field . he also assumes that a more powerful magnetic field will push more on the opposite magnet more than that magnet will push on it
he explained it like this

magnet a =100 magnet b = 10 now what happens to 90 pounds of force gotta go somewhere and thats what causes one magnet to be repelled much much more . he intends to use this principle to get the box to levitate

he also stated this as his equation

UPMAG > DOWNMAG + Gravity

where upmag is the upward repelling force of the magnet
where downmag is the downward repelling force of the magnet
gravity is well gravity

could someone give me a full proof answer to this whole problem . i really do believe this friend of mines lost it . im pretty sure some form of a newton laws prohibits this . if it didnt someone would have done this along time .

i couldnt get the picture to upload so i hope doing this works in explaining

id appreciate any answer to this

february 3 2008

2. Feb 3, 2008

### Staff: Mentor

There can only be one force between a pair of objects. They cannot repel each other with different forces.

3. Feb 3, 2008

### hitspace

meaning that the larger more powerful magnet wont repel more then the smaller less powerful magnet ?i mean if the pull forces are different wont the more powerful magnet repel much more ?

4. Feb 3, 2008

### DaveC426913

This is analogous to saying that the Earth pulls on a rock more than the rock pulls on the Earth. If this were true, there would be a net force in the rock > Earth direction, meaning this rock would be pushing the Earth around.

It would mean we could get free rocket propulsion by taking our giant rocket, disposing of the entire rocket-bit, and instead placing a tiny pebble on the stern plate. The rocket's hugely greater mass would pull on the pebble with great force, far outweighting the force that the tiny pebble could pull on the rocket, and poof! our rocket accelerates willy-nilly across the solar system!

5. Feb 3, 2008

### hitspace

oh no i think he meant the "repulsing magnetic field" not the earths gravity . we are talking about two magnets with two different pull forces .

what this savant friend of mine thinks is that the pull of gravity and the downward repulsion of the top magnet is less then say the magnetic pull force or a magnetic field of 100 or 150 pounds from the bottom magnet . gravity doesnt impose that much force does it ? after all flight wouldnt be possible otherwise . this little idea apparently does much less . levitation.

if all of this is incorrect , i believe it . i just can t put my finger on exactly what law of science and why . knowing how science works is really important to me thats why i ask .

dave i didnt fully grasp your analogy of the pebble and rocket. i was under the impression that we were referring to magnetic fields not gravity . i mean this pepple doesnt have any magnetic force and even if it did . a shuttle is huge i doubt it could support that much mass

i got the diagram to upload i hope it shows what i mean

#### Attached Files:

• ###### thescheme2.jpeg
File size:
38.8 KB
Views:
160
Last edited: Feb 3, 2008
6. Feb 3, 2008

### DaveC426913

Yes. This is why I called it an analogy. The same principle applies. A rock has a smaller "pull" than Earth.

7. Feb 3, 2008

### DaveC426913

OK, here's the thing - (for one, it doesn't require special magnets - a magnet and a big piece of steel will give the same results. but let's go with the magnets.)

The big magnet will - presuming it can lift its own weight - zoom up to hit the top of the box. The impact might cause the box to jerk off the ground... But now that the big magnet is at the top of the box, there are no more net forces except gravity.

And now the box is at rest on the ground. So where does the levitation come in?

Personally, I suspect your friend might be toying with you.

Ask your fiend this question - let's simplify our study of the principles involved by pretending we walked into the room five seconds after the device was set up and set to go but after it does its magnet zooming thing.

We walk into the room and we see a box (which, fortunately, is transparent). Inside, we see a small magnet glued to the lid, and a larger magnet stuck to it.

Now, why would it be levitating?

Last edited: Feb 3, 2008
8. Feb 3, 2008

### hitspace

i dont believe him . i just dont know exactly why hes wrong . meaning what law of science governs it. im just playing devils advocate to try and understand how it all works

secondly the magnet isnt pulling its repulsing with 100 pounds of force .isnt that enough to beat gravity . what my friend says ill see is that maybe a cube about 6 by 6 by 6 inches with a powerful magnet glued to the bottom of a box with its north pole facing upwards . on the lid a small peg has been glued and a magnet with hole will be guided by this peg .its north pole is alligned downwards . because the smaller magnet will push with say 10 pounds of force and the more powerful one pushes with a much greater force at one point the velocity of box maybe 50 or so pounds upward will beat the pull of gravity . now these magnets are constantly applying pressure on each others magnetic field . this constant force will in theory make the net force more going upward then gravities is going downward . i mean you have played with magnets before correct ? well when they repulse they dont stop applying force after the initial contact of the electromagnetic fields .

your saying that the two magnets are neutral . but are they ? how can a magnet that has 10 x the pulling / repelling force be pushed in the exact same way by a much less powerful magnet . i was under the impression magnetism is the association of materials charges . when repulsing a material is pushing the others magnetic field out of its own . when a material has a much more powerful force that extra force must exert pressure on something that is also a law of nature . i dont understand why the magnets would be neutral . i agree though that if they were then the downward pull of gravity would be much much more powerful then that of the upward force of repulsing magnetism leaving the box on the ground with much to be desired .

actually this wont work with steel because its repulsing not pulling magnetic force that we are dealing with . the second we magnetize a piece of steel its not just any old piece of steel it would be a magnet .

Last edited: Feb 3, 2008
9. Feb 4, 2008

### Danger

Basically, it comes down to the fact that they're both attached to the same object. If there was a magnet below the box, and one inside it or attached to the outside of it, then the box could levitate (think maglev trains). Ask your friend what he thinks would happen if he sealed a rocket inside of the box and lit it.

10. Feb 4, 2008

### Staff: Mentor

I think what you guys are probably missing is that that "pull force" is a advertised rating. It doesn't give that force in all situations.

11. Feb 4, 2008

### hitspace

so the advertised rating is not true at all ? i mean ive seen some of these magnets push up almost 100 pounds . they have warning signs on them . r u sure ? and magnets do have pull force ratings dont they ?
(just remembered . if you ever saw mythbusters they used maybe 3 or 4 of these to scale an air vent )

im under the impression that this is not a rocket in a box . after all a rocket would just blow the box up now , wouldnt it ?

i think the whole theory is to harness magnetic fields in a way that we wont need tracks like in the case of maglevs . i totally understand why maglevs work . im just confused how all that electromagnetic energy just goes and does nothing .
...

wait did you say attached to the same object ? but they arent . you see its only the peg coming down from the top and the magnet on the bottom thats glued down then somebody had to forcefully guide another magnet onto that peg not it cant go back down it can only go up so it sticks on the top of the box exerting force .

is there anyway to test this ? i mean cheaply ? ive gotten him to show me the schematics for his so called small scale experiment but large magnets like the ones he wants cost money .alot of money . any ideas ?

Last edited: Feb 4, 2008
12. Feb 4, 2008

### stewartcs

Another good analogy would be to imagine yourself inside the box and pushing up on the ceiling with your arms, and your legs pushing down on the floor. Do you think you would actually cause the box to levitate??

There would be an equal and opposite force (assuming the box walls didn't yield) which would just get you tired and not levitating.

CS

13. Feb 4, 2008

### DaveC426913

Ohhh! I see. They're repelling, not attracting.

Your friend has selective amnesia when it comes to forces. He's not bothering to consider the fact that, when a magnet in the bottom of a box is pushing away from a magnet in the top of a box, that the magnet in the bottom of the box is pushing downward on the box.

Question for clarity from your friend: is he claiming sustained levitation, or is he talking momentary levitation, like a fraction of a second?

This is important. It might be possible to simulate a moment of levitation by taking advantage of the moving elements, inertia and the centre of the mass. i.e. he might get the box to leap off the table an inch or so and take a microscopically longer time to land than expected.

14. Feb 4, 2008

### Mech_Engineer

Let's just say your "savant genius" friend should make a prototype before he spends thousands of dollars on a patent... because this will not work as an "anti-gravity" machine.

15. Feb 4, 2008

### Staff: Mentor

It is true under a limited set of conditions. You do understand, for example, that a magnet's force (whether attraction or repulsion is irrelevant) falls off with the square of the distance between the magnet and the object it is acting on, right?

Also, the rated force is probably for the magnet in contact with ordinary piece of iron or steel. When two magnets are in proximity to each other, the force will be greater than the rating.

Last edited: Feb 4, 2008
16. Feb 4, 2008

### DaveC426913

While true, I think this may lead the OP to bark up the wrong tree. Whether accurate or not, the force of the magnets is not the reason this device will fail.

It will fail because the inventor makes the classic mistake of thinking that a magnet can do work when it is not moving relative to things around it.

17. Feb 4, 2008

### hitspace

so he shouldnt even bother testing this ?

this friend of mine explained this amnesia of force by saying that is compensated by the huge difference of forces between magnets . he showed this in the equation

upwardmagneticforce > downwardmagneticforce + gravity

now i dont know whether the pull force is exactly as advertised but one can see how more powerful magnets have larger more powerful fields

i was under the impression that the energy would be transferred upwards against the top of the box

but a maglev does work and the magnets on the rail arent moving are they ? well i wouldnt know . he doesnt ignore these things just manages to explain them away .

and to be noted . it isnt anti gravity . it still uses basic principles and includes gravity in the equation

Last edited: Feb 4, 2008
18. Feb 4, 2008

### stnbtch15

what it seems like to me after reading everything that is on this one is that your friend isn't acknowledging that there are magnetic fields around the magnets instead of just pulling forces of the magnets. when the magnets are close enough to really affect each other the magnetic fields are what repel each other not the magnets themselves. when the weaker of the magnets gets stopped by the top of the box the magnets will equal out the force in between them so that one magnetic field is larger then the other and the magnetic force between the fields is equal. this will make the upwards and downwards force on the box equal. for example:

if the magnet on the bottom repels with 100 lbs of pressure (just making the numbers easy here not saying they are correct) and the top magnet repels with 50 lbs of pressure the magnetic fields will equal out their pressure somewhere around 3/4 of the way to the top of the box. then the box will have and equal amount of pressure pushing on it on the top and on the bottom. assuming the box doesn't break the only force that isn't canceled out by an equal force in the opposite direction is gravity. therefore the box wouldn't levitate.

however i would like to talk to your friend about his idea because in theory someone could use a stationary magnet on the bottom and a magnet that moves up and down on the top and one spinning somewhere on the side to make the box jerk upwards over and over again causing it to stay in the air. but if the magnets are not continuously moving the box will not levitate.

19. Feb 4, 2008

### Manchot

Newton's third law tells us that the upward magnetic force is equal to the downward magnetic force. They cancel each other out exactly: all that is left is gravity.

20. Feb 4, 2008

### DaveC426913

This is what I don't understand though. The powerful magnet stays inside the box. At some point, the magnet is going to be pushing down on the box! How can he think otherwise!!

But by all means, let him experiment.

21. Feb 4, 2008

### Staff: Mentor

Actually, no, it will fail because a magnet can't exert one force on an object while that object exerts a different force on it. Magnetic levitation, of course, involves no work. He's simply not understanding how the forces add up inside the box.

Last edited: Feb 4, 2008
22. Feb 4, 2008

### Staff: Mentor

No, I absolutely think he should test this. He's not going to believe us until he sees it himself (and it doesn't sound like you will either!).

Btw, there is something else you guys are missing here. If the forces were indeed unbalanced, the entire apparatus wouldn't just levitate, it would go shooting off into space. Unbalanced forces mean there is an acceleration.

And I don't think anyone said it, but the "extra force" on the big magnet (from your post with the diagram) is the force with which the little magnet pushes down on it, causing the big magnet to apply a greater force to the side of the box than the combined weights of the two magnets.

There are three forces at play inside the box. There is the force between the two magnets, the force between the bottom magnet and the box (the weight of both magnets plus the "extra" repulsive force) and the force between the top magnet and the top of the box (the "extra" repulsive force minus the weight of the top magnet). These forces are all in equlibrium with each other.

Last edited: Feb 4, 2008
23. Feb 5, 2008

### stewartcs

Tell him to draw a FBD and sum ALL of the forces, not just these (i.e. this is not the complete equation because this is not the complete system).

CS

24. Feb 9, 2008

This is probably the most simple way to understand what would happen for people who might not be extremely physics savvy: Newton's Third Law of motion. For every action there is an equal and opposite reaction. As long as you're willing to believe in this law, it's simple. The top magnet can only push as much on the bottom magnet as the bottom magnet can push back.

To demonstrate this (even though it's not dealing with magnetic forces) try throwing a piece of paper into the air and as it floats down try punching it. It will put up no fight at all. You'll hardly even feel like you're punching anything. And yet you don't make the sheet of paper go flying across the room. It just moves a foot or so. That's because you can only apply as much force to the sheet of paper as it can apply to you. Therefore, since you're hand doesn't feel much force, you don't put much force on the paper, and therefore the paper doesn't go very far. Now if you threw a dodge ball in the air and punched it, you'll feel much more force on your hand, and the ball will indeed go flying across the room.

If you wanted to try you're experiment without the box it would be easy. Just hold the two magnets in each of your hands. Try pushing them together and you'll experience what I was just was explaining. As much as the one magnet pushes up again you're hand the other one will on the other hand.

25. Feb 9, 2008

### DaveC426913

I'm just gonna go out on a limb and guess that a guy who thinks this is a workable idea is a guy who doesn't know how to do FBDs...