HN Theater @HNTheaterMonth

⬐ johnhenry

Definitely one of those things that's cooler than the HN title implies.

No, what he is saying, is that moving magnetic field, induces current, and can mess up the cheap power supply and/or other components, which can then mess up the drives.

In a server, the power supply is on the other end of the chasis. In a laptop, it's a lot closer to the internals.

> I don't buy that either.

Theory: https://en.wikipedia.org/wiki/Electromagnetic_induction

The forward model: https://www.youtube.com/watch?v=UL_ryxub-RA

The reverse model: https://www.youtube.com/watch?v=J9b0J29OzAU

The big ones: https://en.wikipedia.org/wiki/List_of_conventional_hydroelec... Note: the Three Gorges: 22 GW

For comparison, nuclear power: https://www.nei.org/Knowledge-Center/Nuclear-Statistics/US-N... Largest U.S. nuclear plant: Palo Verde (Arizona) produces around 4 GW.

For home applications: http://www.ebay.com/bhp/hydro-electric

⬐ harshreality

Nobody is suggesting that electromagnetic theory is false. The question is whether there's really a danger from HDD magnets in motion relative to nearby electronics or HDD platters.

- HDDs often live right next to each other (separation of roughly 1cm, front to back).

- Power supplies and their induction coils are right next to the drives in some cases, including for instance consumer grade NAS boxes.

- HDDs tend to have a coil of wire, too.

If HDD magnets overwriting nearby HDD data was a thing, it would be happening all the time.

If HDD magnets in motion in certain orientations were inducing damaging currents in nearby HDDs or in nearby power supplies which then damaged connected components, that would be happening less often but still all the time. Not all chassis designs have power supplies at the opposite end as the disks, and some applications like consumer NAS boxes have them in close proximity to each other.

⬐ quickben

The magnetic head that writes to the disk, is fairly small and close to the platter. The flux is very contained. So that part seems negligible in the overall scheme of things.

⬐ harshreality

Who's talking about the field from the magnetic read/write head(s)? This is about the permanent magnets built into spinning hard drives, and what those permanent magnets might do to nearby disk platters, or, when in motion, might do to coils of wire in nearby electronics.

Either some extremely unfortunate and rare positioning and orientation and motion of the magnet occurred, which barely exceeded the design limits of the drive or power supply or other circuitry (or maybe the laptop hdd or circuitry was shoddy and shouldn't have had a problem but did), or this is a major problem that's gone unappreciated among computer and NAS builders for decades, or it was an extremely unlikely coincidence.

⬐ ars

Do you understand what you are saying?

A person, moving a magnet near a single wire - not even a coil - is going to induce utterly insignificant amounts of electricity.

You'd need lab equipment to even detect it. It will do absolutely nothing whatsoever to computer electronics.

⬐ quickben

Open a powesupply before your next reply.

⬐ ars

What am I supposed to reply to?

Instead, why don't you take a multimeter and see if you can measure any voltage (never mind current) by moving a magnet, by hand, near a single non-coiled wire.

⬐ quickben

Well honestly, I wrote that because I wasn't sure what to reply. I'm taking in five comments about power supplies, tons of wrapped wire, and I get a reply about a single wire.

Anyways, I apologise for being snappy.

⬐ curiousgal

I prefer this video[0] where they go through different iterations to try and improve the speed (by reducing friction and weight).

0.https://www.youtube.com/watch?v=rwt9K9PWMcU

⬐ phkahler

It's a hyperloop!

⬐ rukittenme

Strange question, how energy efficient is this? What exactly is the battery doing and how much energy does it take to do it?

⬐ jacquesm

Energy efficiency is not very high, there is quite a bit of friction.

The battery powers a short section of the coil, the magnets do double duty, they're commutators carrying the current from the battery to the coil and provide the static magnetic field that is one half of the field causing the forward movement, the other half is provided by the magnetic field induced by the current through the coil.

The coil being wound one way (right hand) or the other (left hand) coupled with the direction the magnets are pointed in determines whether it is going forward or backward. If you turned the 'carriage' around it would go the other way.

Elegant.

⬐ quarterwave

Nice demo! Quick back of the envelope calculation for the current to overcome dynamic friction:

I = mu_friction * Mass * grav_acc / (Turns_per_length * Area * Br_magnet)

Say Mass=0.1kg, coil at 600 turns per metre, hand-wave mu_friction=0.2, and a rare-earth retention Br=1Tesla, gives a current of 3A. Maybe more to chug along, would deplete a 2000mAh battery in about 30 minutes. Wire looks about 20 AWG, should get quite hot.

⬐ scoot

Which would theoretically use more energy, levetating the "train", or overcoming the friction?

(I"m not suggesting this design can levitate, just curious about the trade-off.)

⬐ nightcracker

The train never levitates.

⬐ CraigJPerry

Levitating.

Since overcoming the friction can be achieved through approaches like coating the wire in ultra low friction material which will consume no power to operate.

⬐ Someone

Same principle, different application (an electric engine): http://www.youtube.com/watch?v=zOdboRYf1hM, http://youtu.be/CoXboA8Ax7Q (or zillions of other videos)

⬐ aleem

Almost as interesting, this video of a Stirling/Heat engine using just an empty can, sticks and heat for power source:

https://www.youtube.com/watch?v=FCjYZT6FJm4

And a very simple motor using just only a battery and wire:

http://www.youtube.com/watch?v=vCSvNyHorgo

⬐ elsurudo

Could a design such as this work in the real-world, for a real train?

It seems to me that this could be feasible, since the power source is on the "car" itself, and the coil (infrastructure) wouldn't be that expensive to build (apart from the materials, of course). Or is it just too inefficient?

I don't know much about electronics/electromagnetism, admittedly.

⬐ MrBra

Also never forget the implications of the Square-Cube Law http://en.m.wikipedia.org/wiki/Square-cube_law

⬐ elsurudo

Can you explain what you mean by this? I can't find mention of its implications to electricity.

⬐ cma

Probably that as you scale up the size linearly, the volume, and thus weight goes up as the cube, but the surface area goes up as the square.

Since this design relies on closing the circuit by having the magnets rub the wire, as you scale up you have an area in contact with the wire (surface area) going up as X^2, but the downforce due to gravity going up as X^3.

You could add wheels and metallic contact brushes to scale it up. Keep in mind copper is really expensive, and you'd be scaling that up nontrivially too, or the current would fry the wire (I'd think the mass of the copper would go up as the cube too, at least to accelerate at the same rate--acceleration depends on the mass since F=MA, and the mass of the train went up as the cube).

⬐ jarek

A variation where the power source is in the track exists in the real world, http://en.wikipedia.org/wiki/Linear_motor#Train_propulsion

⬐ MrBra

Why I do not know anything about how this works. I thought myself how to code but each time I see this stuff I struggle with the feeling that I can't seem to find a reasonably DIY knowledge builder for basic science branches like this.

How do you start? Help please.

⬐ larrydag

There are some great Arduino tutorials on basic microcontroller usage. They give you an idea on the basics of electronics.

⬐ DanBC

A while ago I would have told tou to buy "the art of electronics", and the student manual that accompanies it, and some cheap electronic test equipement and power supply and a bread board and a selection of useful components, and to then spend an hour or so each week ploughing through the book.

Today there are probably better ways.

⬐ lotsofmangos

Buy this. - Getting Started in Electronics - by Forrest M. Mims, III. - http://www.w5yi.org/catalog_details.php?pid=34&sort=21

It is thoroughly excellent and the electrons all have little faces.

⬐ mikeyouse

Depending on the depth you're interested in, Khan Academy has some pretty good videos on the topic:

https://www.khanacademy.org/science/physics/electricity-and-...

⬐ MrBra

*taught :\

⬐ facepalm

We were taught this stuff in school, although I didn't think of that application then :-) I mean that current running through a coil induces a magnetic field.

Maybe just start with a physics school book?

Edit: in fact current running through a wire induces a magnetic field (actually, just electrons moving, with or without a wire), I guess the coil just gives it direction and kind of amplifies it (it's been a while).

⬐ thornjm

Anyone have a neat explanation for how it works?

⬐ sumnulu

Magnets are serving two purposes; First one as contact point for the coil and completing the solenoid, and the second one to push the battery. Metal coil is generating magnetic field.

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

http://en.wikipedia.org/wiki/Ampère%27s_circuital_law

⬐ huuu

I'm not sure but it looks like the same effect of a homopolar motor: http://en.wikipedia.org/wiki/Homopolar_motor

⬐ kghose

When the train is placed completely within the copper coil, the circuit is closed. A current flows from the +ve end of the battery, round the local part of the coil, back into the -ve end of the battery (the magnets are conducting).

This circulating current generates a magnetic field. Proper orientation of the head and tail magnets leads to both magnets being pushed in the same direction because of their interaction with the generated magnetic field.

This is the force that drives the train.

⬐ theophrastus

We may properly guess that the handedness of the helical copper coil determines the direction the train takes? (left hand rule and whatnot) Connect two loops of opposite handedness and perhaps the train will alternate direction? nahh, probably just get stuck at the transition point.

⬐ higherpurpose

Is this also the first real perpetual motion machine? That thing looks like it could go on forever. Or is it limited by the current in the battery? If it is, could the motion provide back the energy to the battery somehow, and would it be a net positive?

⬐ reledi

Please stop downvoting higherpurpose for being curious and asking a question like this. We all lack knowledge in different areas, that shouldn't prevent us from positively participating because we fear repercussions.

⬐ yetihehe

I would rather see that people are prevented from participating when they have nothing very insightful to say. This policy prevented me from posting some stupid comments and I think this made HN better. You should stop and think before submitting your comment. Otherwise HN will change into another slashdot where stupid uninformed comments are rampant. If there are no repercussions to people who don't think before posting, there will be more people, who don't think before posting ;).

⬐ alan_cx

A question was asked. That implies a lack of knowledge. Given that lack of knowledge, how is one to know if the question is regarded by people who do have that knowledge as "stupid"?

⬐ Someone

I wouldn't downvote it, but "Is this also the first real perpetual motion machine?" indicates that the one asking the question is familiar with the terminology, and even knows that all known perpetual motion machines aren't real. If so, in this forum, I think we can assume that (s)he also can google that term and make some deductions from what (s)he finds. It is not as if (s)he does not have Internet access.

"I googled, and found differing opinions on whether perpetual motion is possible. Is this an example that shows that it is?" would be a better question. It still would surprise me that there are people on HN who would pose such a question about such a simple device, but it would show some intelligence and a will to make an effort to learn. The OP still may have both, but the way the question is posed doesn't show it.

⬐ hotgoldminer

Sure, I can induce that if it is a battery, it is being used as a power source. Others may induce that it is simply a thing with north and south magnetic poles. While I understand I am contributing to the phenomenon, HN threads often derail and become critiques about what HN should and should not be.

⬐ dang

You're right, stopping and thinking before posting is important. (You can also think after posting, and edit!) We want reflective comments and votes as opposed to reflexive ones. But we also want HN to be a place where people are welcome to ask simple questions.

There are many reasons for this. Not everybody knows the same things. It can be surprisingly valuable to go over the basics even when you already know them. And then there's the "stupid question" that so often is far from stupid—often everyone else in the room is wondering the same thing. It usually isn't obvious in advance whether a question is deep or shallow.

Asking simple foundational questions out of interest isn't a problem around here. The finest conversations always welcome them. It's the intellectually petty discussions, where people try to one-up each other with displays of knowledge, that can't handle them.

⬐ None

None

⬐ lerouxb

If I could vote you up 10000 times, I would.

⬐ yoha

Physics isn't mandatory in high schools in the US?

I could not find much about this so any information is welcome: are there federal laws that set the mandatory courses in high school or is it state-dependent? where can we find what these courses are?

For France, I was able to find the following information:

Seconde: http://www.education.gouv.fr/cid52692/les-enseignements-nouv... Première: http://eduscol.education.fr/pid23202-cid46459/programmes-du-... Terminale: http://eduscol.education.fr/pid23202-cid46522/programmes-du-...

Basically, physics are still a mandatory course in all high school.

--

Since I was started with this, I wrote a short explanation on student years before graduation in France:

In France, we count student years away from graduation: Sixième ("Sixth", 6th), Cinquième ("Fifth", 7th), Quatrième ("Fourth", 8th), Troisième ("Third", 9th) are medium high ("collège") while Seconde ("Second", 10th), Première ("First", 11th) and Terminale ("Final", 12th) are high-school.

And we have specific names for our five-year elementary school ("École primaire"): Cours Préparatoire ("Preparatory course/class", 1st), Cours Élémentaire 1 ("Elementary class 1", 2nd) and 2 (3rd), Cours Moyen 1 ("Average class 1", 4th) and 2 (5th). And before that is non-mandatory kindergarten ("École maternelle"): "Petite section [de maternelle]", "Moyenne section" and "Grande section".

All of this is summed up here: http://www.frenchentree.com/living-in-france/education/frenc... .

⬐ bane

No. It depends on the local standards, but generally we have a choice of different sciences we can pursue. When I was in highschool I took Earth Science, Chemistry I, Chemistry II, Biology, Bio-lab I, Bio-lab II. I could have swapped out Earth Science for Physics and one of the labs for a Physics lab if I had wanted, but at the time my maths were poor enough that I decided to stay in the less "mathy" sciences and more lab work.

⬐ BoppreH

The motion depletes the battery, no different than a toy car motor. Yes, you could theoretically provide energy back to the battery. No, it would not be a net positive. It would deplete the battery faster, for a net loss because of unavoidable conversion inefficiencies.

Edit: if you saw this video, realized there was a battery involved, and your first thought was "Perpetual Motion Device!", you might be delusional or severely misinformed. For your own sake, please research the topic a bit more and avoid echo chambers.

⬐ devindotcom

Quite an unnecessary, mean-spirited, and mistaken edit.

OP, your confusion is perfectly normal. I came here to post that my dad would think this is a perpetual motion machine. He simply is not familiar with the physical laws that make such a thing impossible and likes the idea of it.

⬐ dang

This comment would be better without the second paragraph, which is needlessly personal and meta.

The first paragraph is splendid.

⬐ BoppreH

I agree the second paragraph is personal and meta, and I don't like it either.

But if I ever go down a rabbit hole and end up detached from reality, I would love to have someone to tip me off. It's like pointing out someone's fly is open.

Maybe OP is perfectly sane and just got confused on the physics of this system. Maybe they are very young. Or I misread their comment. In that case, OP has my deepest apologies.

It's just that perpetual motion is a well known trap for intelligent people; and expressions like "first real perpetual motion machine" and "provide back the energy to the battery somehow" make me worry that a fellow human being is going down the wrong path.

⬐ dang

Thanks for clarifying the helpful intention behind the comment. That does make sense. Probably all it needed to do was make the intention a bit more explicit, so it wouldn't be mistaken for one-upmanship.

By the way, your reply was so neutral and respectful that I didn't realize you were the original commenter. That's remarkable, so thank you.

⬐ rootlocus

Anyone else notice the Berta Lovejoy comment? :D

⬐ twkl

I wonder who made the stupid decision to remove the downvote feature in the YouTube comments. I heard that they couldn't implement it because Google+ only has upvotes, but why they don't simply allocate another column in their database is beyond me.

⬐ ohitsdom

If I had a dollar for every time a manager said "Just put another column in the database"...

But seriously, I doubt it was a technical reason. Probably wanted to drive more positive behavior.

⬐ idoco

http://www.reddit.com/r/OutOfTheLoop/comments/2g99vg/who_is_...

⬐ None

None

⬐ pilif

Nope. Once the battery is depleted, the motion will stop.

⬐ blacktulip

Oh there are batteries. I thought it was just a big magnet

⬐ onion2k

Even if it was just a magnet it still wouldn't go on forever. The second law of thermodynamics applies to everything, including permanent magnets.

⬐ cookingrobot

The way you phrase that, it sounds like you're saying there could be a machine that operates due to permanent magnets, but depletes them as it runs, so that eventually they're not magnetic anymore. That's an interesting proposition.. Is there any reason a machine like that could or couldn't exist?

⬐ onion2k

There are. They're called "Magnet Motors". You see a lot of them in 'free energy' and 'perpetual motion device' circles. They're not useful because you can't get much energy out and, as I said, the magnets stop being magnets. People most often don't understand the second bit which is why they think they've cracked humanity's energy problems.

⬐ cookingrobot

My intuition is that magnets are in a lower energy state than non-magnets, because I would imagine it takes energy to unaligned magnetically aligned molecules.

Is that not the case?

⬐ lotsofmangos

As far as I am aware, the field of a permanent magnet is down to the alignment of the electron spins, the more aligned they are, the further out the field reaches instead of the flux lines being closely folded up and canceling out. However there is not a difference in energy for different alignments, so you cannot get work out from reducing the extent of the field.

edit - think about the difference between having one big wave or millions of small ones that add up to the same energy as the big one. There is no energy difference between the two systems, but if you are standing on a cliff overlooking the sea, only the big one is going to get you wet.

⬐ cookingrobot

Your answer makes sense to me, but contradicts onion2k's "magnet motor" comment. Have you heard of that concept - any thoughts?

⬐ lotsofmangos

I have heard of them and I know at least three people who have tried to build them. I have never seen one work and I know of nobody who says they have seen one work in person.

edit - also, I went and had a bit more of a look and it turns out there is an energy difference between magnetised and demagnetised materials, but it is very small. One thing is that spontaneous magnetization happens and it wouldn't occur if the energy difference was large.

⬐ ealloc

Actually, the 2nd law doesn't apply to everything. For example, a single classical planet orbiting a sun will orbit forever. Or, gas particles in a cube box if their velocities are perfectly perpendicular to one side of the box. Or a simple harmonic oscillator.

In many physical (classical) systems there is a set of generalized coordinates of measure 0 which does not obey the 2nd law.

⬐ onion2k

The second law isn't just "All thermodynamic systems increase in entropy." There's an important bit that follows "..due to the dissipation of energy." The systems you describe are all still limited by the second law - they just won't increase in entropy because they're not dissipating energy. They're all in equilibrium.

⬐ nly

I have some old Ladybird Classic books[0] that I inherited from my father, who had them when he was a kid in the 60s. I remember one of them included something like this. It may have been [1]. I can't imagine a modern childrens book encouraging kids to take apart batteries or attempt their own electroplating :-)

[0] https://en.wikipedia.org/wiki/Ladybird_Books#The_classic_Lad...

[1] http://www.ebay.ie/itm/VINTAGE-LADYBIRD-BOOK-Magnets-Bulbs-a... (several pics of inside)