Special Repelling Magnet Shoes

physicsfrenzy

Hello,

I am new to the forums, my name is Brandon. I have just recently graduated high school. I graduated from my physics class with a 97% for the year! yay!

But off to my question...

I have been thinking of a cool project that involved 4 neodymium magnets and using the repulsion force between them to act like a "spring" effect to make you able to jump and run at increased increments.

Here is how it works:

You have two magnets for each shoe. You contain the two magnets inside a non-magnetic material so the axis are lined perfectly underneath the shoe. I am not sure of the complete contraption yet but I was thinking if you used magnetic repulsion it should act like spring shoes, well.... my theory anyways. Could this possibly work?

Thanks for the help. And hello again.

Brandon

Waterfox

Then why not just use springs? The only advantage I see is that springs may fail earlier due to wear.

physicsfrenzy

I just do not see springs being stronger than some magnetic repulsion.

Bobbywhy

physicsfrenzy, Welcome here to Physics Forums!

If you put some powerful magnets in your shoes, wouldn't you need magnets on the ground to repel them?

CWatters

http://suspensioncoil.com/coil-spring-shoes/?

HallsofIvy

You got 97% in physics and did not learn anything about "conservation of momentum"? Very sad.

Your set up has all magnets as a system contained on your body and so cannot change the momentum of your body. They cannot add any speed at all to your body.

NascentOxygen

Hi physicsfrenzy. Yes, it will work, though the efficiency gain may not be as spectacular as you hope. One thing you may not have considered is the gradual loss of magnetism of the ground-contacting magnets due to the shock of hitting the ground hard with each step; a rubber sole should go a long way to easing that. I can see that a well-designed containment box will be essential.

You may find that best efficiency is associated with a kangaroo-bound gait, keeping feet together throughout. Some adaptation of ski poles might reassure the beginner. The extra weight compared with spring shoes will help develop good calf muscles!!

Good luck with your physics career.

ZapperZ

I still say that Bobbywhy brought up the most sensible question that makes this scenario rather dubious. What is it going to repel against? The "ground" is usually non-magnetic! Try it!

Zz.

Jimmy

This is akin to pulling yourself up by your bootstraps.

HallsofIvy

PhysicsFrenzy said clearly in his first post that he would have magnets with opposing poles in each shoe. He seems to be under the impression that that would cause a net upward push. As I said before, he simply does not comrehend "conservation of momentum".

CWatters

When running the tendons in your legs act as springs to store and release energy at different parts of your stride. Amputee runners use carbon fiber prosthetic legs with considerable spring built into them. Some time ago it was questioned if this (and their reduced weight etc) gave them a potential advantage over able bodied runners. Would their artificial springs be more efficient than those of real legs? The answer is apparently no...

http://www.colorado.edu/news/release...age-prostheses

http://jap.physiology.org/content/108/4/1012.full

allowing...

http://www.popsci.com/technology/art...-championships

DaveC426913

To get this to work - even in principle - here's what you'd need to do:
1] Arrange the magnets on your feet so that they are all pointing the same direction - say, south poles downward (or even more simply, one large sole-shaped magnet).
2] Arrange magnets in the floor so they are all pointing with south poles upward.

Now your shoes will be repelled from the floor.

In theory, this would provide a springlike effect. If you jumped off a chair onto the floor, the magnets would repel and bounce you back up like a pogo stick.

Unfortunately, in practice, there are several problems:
1] You could only do it in a controlled environment where you could line the floor with magnets. and you cannot simply space them out. The field must be uniform. You'd have to line every inch of the floor with magnets.
2] It would be impossible to stand upright, let alone jump, let alone run. It is equivalent to trying to stand upright in a swimming pool by strapping a beachball or floaty noodle to each foot. I've tried it. It's impossible. But it's a lot of fun to try.
3] The magnets would try very hard to flip over. You would almost certainly sprain both ankles.

While it would not be of practical use, it could be a fun amusement setup. But you would absolutely have to wear full padding and a helmet.

physicsfrenzy

Thanks for the tons of feedback already wow!

HallsofIvy,

I do know what conservation of momentum is. You can not change momentum between two objects that collide.

But i do not see where they are colliding. Its acting like a spring effect like springs. One magnet on the bottom and one on the top with repelling forces between them. If springs work wouldn't this? I guess I got my question answered.

Thanks everyone!

Integral

You all need to read his post a bit closer. He is putting a pair of opposing magnets within the shoe. So you would be walking on a cushion of magnetic levitation. Sounds like fun.

Two magnets might not be enough to make this work, also you would need to tune the shoes to the weight of the person wearing them. The magnets would always be pushing the soles of the shoes away from the uppers so would need to be very well build or they will self destruct.

Not sure if you could contain all of the magnetic field within the shoe so you would tend to pick up stray bits of iron as you walked. Don't try to walk across a iron plate, you just might lose your shoes!

CWatters

They don't have to touch in order to "collide". Imagine a steel ball coated with rubber. The steel part of the ball doesn't have to come in contact with the ground for the ball to collide with it, it's just that there is a springy rubber layer in between. That rubber layer could be replaced by any number of alternatives (such as two layers of N to N magnets forming a spring).

If the springs/magnetic springs aren't fully compressed (eg they don't "bottom out" or run out of travel) then you could think of each step as an "elastic collision" rather than an "inelastic collision"

http://en.wikipedia.org/wiki/Elastic_collision
Conservation of Energy

http://en.wikipedia.org/wiki/Inelastic_collision
Conservation of Momentum

It wouldn't be a perfect elastic collision as some energy would be lost heating the springs but perhaps close enough.

OmCheeto

It does sound like fun. And we discussed the hazards of using magnets a few days back.

Someone suggested earlier that it would be just like springs. I think it would be a bit different, as springs are linear, and magnets are not, in their force vs distance equations:

springs: F = -kx

opposing magnets:



What the hell does that mean?

hmmm.... If one merges all the variable constants, it looks like the equation becomes: F=-k/x²

Springy, but different.

Unfortunately, I don't have the willpower today to solve whether or not a magnetic-springy shoe would be economically feasible to produce as a world commodity, but... I wonder if this technology can be used somewhere else.......





-------------------------------
The physics of mud, will kick your butt, every time......

HallsofIvy

That is one consequence of "conservation of momentum". It is NOT "conservation of momentum" itself. "Conservation of momentum" says that the momentum of a system cannot be changed except by an external force. What external force is acting on you here?

You said "You have two magnets for each shoe. You contain the two magnets inside a non-magnetic material so the axis are lined perfectly underneath the shoe."
Now it sounds to me like you are having two magnets oppositely aligned in each shoe and trying to use the magnetic repulsion of the two magnets in the shoe to act on the body as a whole. Everyone else is talking about a situation in which there are magnets in the shoes acting against magnets in the floor. If that is what you intended please say so.