# Tag Info

44

Your approach is incorrect. You cannot do this calculation by considering that the energy absorbed by the object is converted into a change in gravitational potential energy. For one thing the object would just get hot and radiate away most of the energy and for another this is a dynamical problem, you have to be able to accelerate the object upwards. What ...

36

The "trick" is that the cane he is apparently holding is actually firmly attached to the platform. A rigid piece goes up his sleave, then to a harness that holds his whole body up. For more about this type of magic trick device, google "broom suspension" or "aerial suspension harness". No electric or magnetic fields were abused here. Image Credit: ...

21

You would feel weightless if every part of your body of mass $m$ would be subject to an upward force equal to $m$ times the local gravitational acceleration $g$. Such an exact part-by-part cancellation is not going to happen via diamagnetic levitation as utilized on the frog in your example. Not only does this levitation couple according to magnetic ...

21

Olin Lanthrop clearly gave the most plausible explanation. But just for fun, let's just assume this was an electromagnetic trick. Would that be possible? First - let's do this using electrical charge: how much charge would you need to allow levitation, and what would the potential have to be? Some assumptions: 70 kg guy 40 cm levitation (based on apparent ...

13

The references in other answers to the Wikipedia pages about Earnshaw's theorem and Magnetic levitation are right on; you absolutely cannot have stable, static magnetic levitation using only ferromagnets. However, at the time of my posting, both other answers contain misinformation. Kakemonsteret's answer is incorrect*, because Earnshaw's theorem is not the ...

12

A magnetic field cannot penetrate a superconductor; since there's no resistance to the flow of electrons, a current is immediately created in the superconductor by the field, and the field produced by that current opposes the original field. This is ordinary magnetic induction, but with zero losses because of the superconductivity. Essentially, whenever a ...

10

As explained on this page, Earnshaw's theorem says it's impossible to have perfectly stable magnetic levitation where none of the fields are changing with time. But as is also discussed there, it is possible to have levitation that appears stable to the naked eye if the the currents that create the magnetic field continually adjust to small movements of the ...

9

First let me make it clear I don't on a Hendo engine and I've never seen the design for one, so what follows is based on what I've found by Googling and what seems intuitively obvious. The Hendo engine uses a technique called electrodynamic suspension. This can get very complicated very quickly when you try to do the calculations, so I'll just describe it ...

9

The force of radiation pressure is $F=P/c$ for absorbed radiation or $F=2P/c$ for reflected radiation, with $P$ the power and $c$ the speed of light. If you want to generate 750 N of force, you need (a) a radiation source of 100 GW and (b) a mirror that reflects so well that nor the mirror, nor you will be vaporized in an instant. Update: CuriousOne ...

8

Your consideration implies you have a device that can convert laser light with 100% efficiency and convert it to mechanical power. This is theoretically possible, but there is not much of physics. You still need some ladder to climb along, and building a space elevator requires much tougher materials than we currently know. In practice, you would have to ...

8

Lookup Optical Tweezers. The limitations of the technique are due to the damage thresholds; see laser ablation. This idea has been used extensively in science fiction, especially when implemented as solar sails. It's even practical for some applications, as noted in the article. But laser propulsion from the ground suffers losses due to the atmosphere. ...

7

Water is a diamagnetic material and like most other non-ferromagnetic materials it does interact with magnetic fields but with much weaker interactions than you are used to from fridge magnets and the like. However, if you crank up the field to something like hundreds of thousands of the Earth's magnetic field - about 10 Tesla will do - then you do get ...

6

Yes, it is possible to magnetically levitate molten metal. This is not due to ferromagnetism however. As seen in the below references, the metal sample is placed within a tapered conducting coil, which carries alternating electric current in the ~400kilohertz range. This sets up a magnetic field gradient inside the coil and causes eddy currents in the ...

6

This is simply a matter of force balancing. The only forces on each magnet are gravity and the magnetic repulsion from the neighbors. The top magnet must be repelled from below with a force equal in magnitude to the force of gravity on it. The next magnet down has not only its own weight pushing down, but the weight of the one above it as well. This is an ...

6

Yes, the frog will be repelled from the field if the field is non-uniform. Its magnetic moment is given through the susceptibility of Water $\vec \mu = V \chi \vec H$ and $\chi_\mathrm{water}\approx -9\times 10^{-6}$ Lets say the average field over the Frog is $\mu_0 H = 10\;\mathrm{T}$. This results in an induced moment of $\mu = -0.3 \mathrm{Am}^2$ ...

5

As lurscher mentioned in a comment, you're using the wrong units for magnetic susceptibility. $\chi$ is actually a dimensionless number that is related to the magnetic permeability of a material relative to that of a vacuum. I think you were mixing it up with the molar magnetic susceptibility, which is $\chi_\text{mol} = \mathcal{M}\chi/\rho$, where ...

5

This phenonemom has also been called Quantum Locking. The term Quantum comes from the fact that superconductivity is a quantum phenomenon and the Locking comes from the fact that magnetic fields are confined or locked into narrow tubes going through the superconductor. In terms of applications - this is basically a form of magnetic levitation using ...

5

This paper describes the effect in some detail. Stable levitation is caused by a combination of the Meissner effect, and of flux pinning in Type-II superconductors. The Miessner effect is the property of superconductors which prevents magnetic flux from penetrating the superconducting material (beyond the penetration depth). It occurs because the applied ...

4

Sadly the Meissner effect can't be used as an anti-gravity device. If you lay under the magnet and put the 3mm superconducting disk and car on top you would indeed be squished. The presenter does use the words "in my hand", but I suspect this is just poor phrasing and I'm sure he is not suggesting he could lift a car in one hand using a superconducting ...

4

The feeling of weight is caused by contact forces acting on only parts of your body: forces like the pavement pushing on your feet, air rushing past certain parts of your body as you fall at terminal velocity, the floor of an elevator pushing with reduced force on your feet as the elevator starts its downward trip. Basically you feel one part of your body ...

4

Given a weight Knowing the weight is not enough. Each material has its own magnetic susceptibility, which can even be a tensor for a crystal. We would need to know the weight and the magnetic susceptiblity to know how the material would behave in a given magnetic field. For example diamagnetic materials experience a force in a direction of ...

4

TL,DR: Magnetic coupling results in lower transmission of sound energy than physical contact Controlling what surfaces vibrate gives more control over sound generation The same benefit could be achieved with other forms of isolation (e.g. foam) but it wouldn't look as cool. It is bunk, mostly. A magnetically levitating speaker maintains a ...

4

Or at least "functions" as a monopole? I'm afraid not. A magnet is a magnetic dipole and there is, as far as I know, no configuration of magnetic dipoles that can give a monopole field.

4

Acoustic levitation requires a material medium to transmit the sound waves that suspend the object you want suspended. The object must contact the medium in order to be suspended. If the object is made of antimatter, it will instantly annihilate upon contact with the material medium that transmits the acoustic waves. You can't transmit acoustic waves in ...

4

Laser is stimulated emission of highly energetic photons. Fundamental use of laser is heating, propulsion is very distant aim which lasers can achieve. Few kW rating lasers can actually lift the mass (very small values though) because incident energy beam has momentum associated with it. Your assumption is not correct as you are comparing heat energy with ...

3

There's a lovely children's novel in which much the same idea is employed for building a "perpetumobile", something that cannot be possible for all we know about physics. The easiest law stating that it can't work is Newtons third law: for every force (like the one that levitates the human) there must be an equal and opposite counter force, in this case ...

3

What you want to investigate is called a Halbach array. You will still need a guide rail for the train, but it will pick up off the track at very low speeds. See http://en.wikipedia.org/wiki/Inductrack for an example.

3

I'm not sure why you expect that energy conservation should be broken. Recall that it does not necessarily cost any energy to hold something in place. A table does not expend any energy in keeping an object from falling to the floor.

3

In short, no, at least not at this point. Unfortunately I was not able to read the entire article, but what I understood from the abstract is that it was only meant for very small volumes and masses, but if they did manage to levitate a cup of coffee, that is a step in the right direction. But there's another problem with this method - it uses ...

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