Hacked Gadgets Forum

June 28, 2010

Lenz’s Law – Magnet falling slowly in Copper Pipe Demonstration

at 5:07 am. Filed under Complex Hacks, Educational

If I learnt about Lenz’s Law in high school I must have forgot about it. Watch the cool demonstration above where a stack of neodymium ring magnets are dropped into a copper pipe. Of course copper is a non magnetic metal so the magnets will not stick to it. You would probably guess that the magnets would simply fall at the same rate as if they were just dropped. Well if that is what you thought you would be mistaken. Due to Lenz’s Law the magnet falls very slowly through the pipe. Watch the video below for a good explanation of what is going on here.

“Lenz’s Law applies the principles of energy conservation to situations that involve forces in electromagnetism. To see an example, move a magnet towards the face of a closed loop of wire (e.g. a coil or solenoid). An electric current is induced in the wire, because the electrons within it are subjected to an increasing magnetic field as the magnet approaches. This produces an EMF (electro-motive force) that acts upon them.”


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9 Responses to “Lenz’s Law – Magnet falling slowly in Copper Pipe Demonstration”

  1. Haku Says:

    Fun science!

    It also works with aluminium pipe, weirdly satisfying when you try it yourself.
    The only practical applications of eddy currents I’ve learned of so far is the braking mechanism of rollercoasters, because it always works, doesn’t produce any friction (and subsequent wear) and doesn’t need an electricty source.

  2. Inventorjack Says:

    @Haku: Eddy currents are useful in a multitude of areas. They’re important in metal detectors, some vending machines, certain types of sensors, they’re key to induction heating, and as you mentioned, can be used for braking.

  3. Inventorjack Says:

    In fact the Wikipedia article for eddy currents (http://en.wikipedia.org/wiki/Eddy_current) lists about 20 applications in which eddy currents play a role.

  4. NatureTM Says:

    When I saw the vid, I said, “whoh!” loud enough to see my cat jump out of the corner of my eye.

  5. ipad case Says:

    is amazing what copper can do

  6. Jared Says:

    It would be cool if you could see the magnet
    falling from the side rather than having to
    look through the end of the pipe. How would
    the effect change if long thin holes were cut
    along the axis of the pipe hall?

  7. Orville Thompson Says:

    I bought an expensice neodymium 1 7/8 inch diameter cylendrical magnet, axiel magnetized; and observed the levitation effect of dropping the magnet through a 36 inch length of 1 1/2 (ID) schedule 40 copper pipe. Pursuant to your video presentation, I slit the copper pipe, full length (“breaking the circuit”, as your experiment demonstrated). When I dropped the magnet through the split pipe, I expected the magnet to fall un-impeded, since I surmised that the induced current could not complete it’s circuit path. Much to my dissappointment, there seemed to be no difference in the magnetic levitation effect. Also, I coiuld not detect a voltage potential, not any current when I bridged the slit with my voltmetef and milliamp meter.

    Can you help me understand why I miss-understood the essence of your explanation and the video demonstration?

    Just using a simple work calculation, I had calculated that substantial cutrrent could be harvested by a foot puond calculation. 1 foot pound is the energy required to raise a 1 pound weight one foot high in 1 second against 1 G (gravity). Conversely, I expected that the induced current (and it’s resulting magnetic field) was restraining the free fall of the magnetic by exerting the opposing magnetic field against the weight of the cylendrical magnet falling towards 1 G (gravity); There’ by using the conservation of energy postulation, the energy being “stored in the magnetic flux” could be harvested by way of tapping the induced current from the pipe.

    Puzzled Electrician

  8. Orville Thompson Says:

    Sorry; MY third word was miss-spelled! EXPENSIVE was the intended word.

  9. Most Powerful Magnet in the World - Hacked Gadgets – DIY Tech Blog Says:

    […] at 6:30, they are dropping an aluminum tube through the magnetic field demonstrating Lenz’s Law, we saw Lenz’s Law in action here but the results are a bit more impressive with a super huge […]

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