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Can someone help me explain this?

  1. Aug 1, 2012 #1
    I've only taken one physics class. I'm not too knowledgeable yet in science, but I was hoping someone can help me explain this video to my brother.

    http://www.youtube.com/watch?v=zqG-TL0WnjE&feature=BFa&list=HL1343828606

    I'm assuming he has a battery in one of the wooden blocks that holds the final contraption up. Although it looks very convincing, my brother wants me to build one. Maybe someone could give me a good reason not to waste my time hah.

    Thank you guys.
     
  2. jcsd
  3. Aug 1, 2012 #2
    The final machine spins the opposite direction as the example devices move. If the device would move as s/he demonstrated in the beginning, it would be spinning the opposite direction. DEBUNKED! And no need to even talk about energy!
     
  4. Aug 1, 2012 #3
    Actually if you look at the green skateboard wheel the magnets start close together then separate as it moves away. The same is for the final guy. Also important to mention, I don't think this were all built by the same person.
     
  5. Aug 1, 2012 #4
    You're right. It's just the middle of the three that moves in the opposite direction. Either way, the energy conservation always works.
    I wouldn't think of it as a waste of time if you have fun and explain to your brother why it won't work. In case you don't know, the reason it won't work is that energy in a closed system (there is no flow of energy in or out) will stay the same. Since there must be friction transporting energy from the system into the environment, there must be energy being transported in.
    But building might still be fun.
     
  6. Aug 1, 2012 #5
    Thanks you DrewD I agree. I guess ill just try. A question I do have, if you don't mind.. If gravity pulls down a magnet which exerts a force against the other magnets causing it to rotate. Will this force change if the magnet is stronger? I'm assuming so, i guess im excited now..
     
  7. Aug 4, 2012 #6
    I have to confess that last one weirded me out. I can't say for sure how it works. My tentative guess, though, is that it's a flywheel effect. You notice how it's pre-loaded. The initial locked position has the cam raising the upper bar against gravity, so you're starting off with PE. I'm surprised at how long it ran without seeming to slow, but he did force it to a stop at the end. If he hadn't, we might see it stop on its own in another minute or so. I'd say we're looking at a kind of flywheel that gets its initial push from what amounts to a pre-loaded spring.
     
  8. Aug 5, 2012 #7

    Drakkith

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    Staff: Mentor

    I notice that the machine didn't speed up after it's 1st turn...
     
  9. Aug 5, 2012 #8
    I'm not quite following what you mean. A stronger magnet, with all else kept the same, will exert a greater force compared with a weaker magnet. I don't understand why that excites you.
     
  10. Aug 5, 2012 #9

    Drakkith

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    Staff: Mentor

    There are two forces to think about. The first is the force between 2 magnets. This gets stronger with stronger magnets. The 2nd is the force of gravity. This only gets stronger if your magnet has more mass. The key to both of these forces is that they are effectively "one way" energy generators. What I mean is that it takes just as much energy to lift something up against gravity as you got by having it fall, and you have to expend as much energy to push or pull magnets apart as you generated by letting them come together or move apart in the first place. It is not possible to generate more energy than you input into the system.
     
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