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What Happens When You Drop A Magnet Inside A Copper Tube [video]

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Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#111

Post by huhtenberg »

IgorPartola wrote: post #2

Yup, it's pretty cool. This was one of the most impressive demo's my physics professor did in our freshman physics class. The point is that as the magnet is falling through the copper tube it creates an electric current which then creates a magnetic field in the opposite direction of the magnet's movement. In other words, this is the practical application of the Right Hand Rule [1]. Two fun facts about it: first, if…

> ... nothing special about the tube being made of copper. Any conducting substance will do.

Any non-magnetic conducting substance that is. Otherwise the magnet will just stick to the tube wall.

Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#113

Post by hurowits »

taliesinb wrote: post #20
IgorPartola wrote: post #2

Yup, it's pretty cool. This was one of the most impressive demo's my physics professor did in our freshman physics class. The point is that as the magnet is falling through the copper tube it creates an electric current which then creates a magnetic field in the opposite direction of the magnet's movement. In other words, this is the practical application of the Right Hand Rule [1]. Two fun facts about it: first, if…

You can also think of it as magnetic flux lines encountering "drag" as they pass through conductors. The limiting behavior of this view is in type II superconductors, which entirely "pin" flux lines -- they present an effectively infinite resistance to the movement of flux lines. That's why a magnet levitates over such a superconductor. [1] You can even image these "vortices" directly [2] [1] http://en.wikipedia.org/…

You might wanna take a look at this video: http://www.youtube.com/watch?v=VyOtIsnG71U

Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#114

Post by dfox »

tall wrote: post #64
laureny wrote: post #37

Earlier quoted context omitted.

> It'd be completely impractical, of course, but a whole lot of fun. And at the end of the ride, you want to take a selfie and email it to all your friends but you can't because your phone is fried.

actually not true, modern phones use SSD, and don't really get affected by magnets in the way you might expect.

Even hard disks are not affected by external magnetic field in the way most people expect. Strong magnetic fields interfere with the operation of drive (seeking voice coil) but accidental erasure of data on platters by external magnetic field is relatively improbable.

Generally most of the damage caused by strong external magnetic fields to any electronics are caused by second order effects, i.e. something gets confused and causes data-destroying failure.

Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#115

Post by Angostura »

tedsanders wrote: post #25
TrainedMonkey wrote: post #19

If magnet was not rotated when dropped through the tube, would it simply stick to one wall in case of slightest imbalance?

No. Because copper isn't ferromagnetic, it will not be magnetized by the magnet, and consequently the magnet and the copper will not be attracted to each other. (In fact copper is diamagnetic, so it will actually slightly repel.) Source: I am a magnet scientist.

So what would happen, minus the spin - straight through at roughly G?

Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#116

Post by dfox »

noir_lord wrote: post #56
malandrew wrote: post #48

Earlier quoted context omitted.

That's it? I was under the impression that copper was far more expensive and is the reason why expresso machines are as expensive as they are.

Copper compared to many metals isn't particular expensive per KG, it is just relatively expensive in the class of metals that we use a crapload of (for example aluminimum is around $1.8 per KG) it is still much cheaper than tin at ~$22. The main reason that copper is so valuable is it has so many uses and is very easily recycled(I saw an estimate that said 80% of all the copper ever mined is still in use) so holds it…

Copper and aluminum are two commonly used metals that are manufactured by relatively costly process that at the same time allows essentially complete recycling.

On the other hand there are not that many uses for pure copper (most of them are electricity related) as there are many other metals or copper alloys that are significantly cheaper.

Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#117

Post by dfox »

asteli wrote: post #44

This effect gets used in modern trains and roller coasters in the form of linear eddy current brakes. In practice, this looks like an electromagnet that's held just over the rail. More reading: http://en.wikipedia.org/wiki/Eddy_current_brake

With electromagnet and iron rail the same effect is used for almost an century on streetcars under the name "electrodynamic brake". Idea is that single assembly combines this for small braking strengths and friction braking for complete stop (the electromagnet is on springs and can come into complete contact with rail, which is used as equivalent of parking brake).

Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#118

Post by dfox »

jules wrote: post #29
deletes wrote: post #10

Where can you buy something like that. A magnet is around 150$, but I have no idea where to get a copper tube of that thickness.

It also works with a small neodymium magnet which can be bought for less than $1 and a small copper plumbing tube which costs about the same.

With thin tube the effect is not noticeable on the outer surface. Essentially, thicker tube means more pronounced effect.

Re: What Happens When You Drop A Magnet Inside A Copper Tube [video]

#119

Post by adsr »

noonespecial wrote: post #99
adsr wrote: post #27

Earlier quoted context omitted.

A kg is about $7 at the moment it seems, so suppose that's 5 kg then $35.

A quick browse over at onlinemetals leads me to believe that you're probably off by a factor of 10x-20x. http://www.onlinemetals.com/merchant.cfm?id=1288&step=2&top_...

That may be, but most of that markup is probably in the part it self, if you compare to a steel tube of the same dimension you'll see an indication of that. I was going by the current price the metal trades for, that is, a ballpark figure as something to "begin to imagine" what it could cost based on the material alone.
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