Is Aluminum Magnetic? (2013) | Hacker News Reader

Is Aluminum Magnetic? (2013)

terpconnect.umd.edu

47 pointszeeshanm17 comments

On the subject of interesting magnetic effects, a lot of people don't know that pretty much all matter is magnetic, just that the strength of the interaction is a lot smaller than what we're used to with ferromagnets.

All materials exhibit a diamagnetic (pushes against the field) effect, but in many materials, that effect is overwhelmed by a competing paramagnetic (pushes in the direction of the field) effect. Most of the things we call "magnets" exhibit ferromagnetism, which typically produces much stronger forces than either of the previous two.

H2O is particularly interesting, because it's actually diamagnetic, and will push away from magnetic fields. Given a strong enough magnet, you can have a lot of fun with this effect by putting common water-filled objects in its field: http://www.ru.nl/hfml/research/levitation/diamagnetic/

Another fun fact: Magnetic fields are a consequence of relativity and length contraction of electric fields.

http://physics.weber.edu/schroeder/mrr/MRRtalk.html

This video also talks about it: https://www.youtube.com/watch?v=1TKSfAkWWN0

Nitpick: relativity can explain magnetism, not cause magnetism.

True, it explains them in terms of electric fields, but we still don't know what those are.

We know:

http://en.wikipedia.org/wiki/Electric_field

http://en.wikipedia.org/wiki/Electric_charge

http://en.wikipedia.org/wiki/Quantum_electrodynamics

An electric field is generated by electric charge and time-varying magnetic fields

Charge is the fundamental property of forms of matter that exhibit electrostatic attraction or repulsion in the presence of other matter. Electric charge is a characteristic property of many subatomic particles.

Nitpicking again - the fields are a working mathematical description but, as far as I know, we don't know if or in what sense they are real things, whatever real thing even means. The electrical and magnetic fields change when you switch reference frames, so that does not sound like something that really exists independent of an observer. The vector potential on the other hand does not change but it does not seem real either because it has gauge symmetry.

We know that the A field is more fundamental (at least Feynman thought so):

http://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect

Interesting. Does it explain permanent magnets too?

So a MF is just a twisted EF diffusion ?

/me on his way to watch that video

I don't think any of these examples actually imply anything about whether aluminum is "magnetic" (for any definition of magnetic).

All the demonstrations rely on a changing magnetic field, either because the magnet is moving, or because the aluminum is moving. This induces an electric field in the aluminum (as it would in any conductor) which moves the aluminum, induces a magnetic field which moves the magnet, etc., but is independent of whether aluminum is ferromagnetic, paramagnetic or diamagnetic.

I think the way to say it is that All is diamagnetic.

Too bad the videos are not done by Bill Nye.

Electromagnetics is awesome, nonetheless. :)

you mean AL-e-um? (w/ British overtone.. :)

The one thing I really took away from this (and unfortunately not entirely relevant) is that American English also has it's own SPELLING of Aluminium, not just pronunciation.

It makes the difference in pronunciation make a lot more sense to me. Are there (m)any other cases of this, where both the spelling and pronunciation are different? Leisure, herbs, etc.? (Lift/Elevator doesn't count)

http://en.wikipedia.org/wiki/American_and_British_English_sp...

I was hoping for a bit more with regards to significant pronunciation differences. Not just spelling differences.

As I remember it the British spelling and pronunciation of Aluminum changed a number of times including using "Aluminum" for a while.

Reply on news.ycombinator.com