Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Can magnets on a cylindrical object be used for projectiles?

Tags:
  1. Mar 30, 2017 #1
    What I mean is if I have 2 cylinder objects made out of a light wood for example with 6 or so magnets on either face spread evenly and another magnet behind it causing it to spin could it generate a good amount of torque to shoot a small projectile between the two cylinders. To give you a better image you may have seen people putting magnets on their fans and holding another magnet close to it causing the fan to rotate. I'm talking about something similar but with a lot more pull (10 kg and maybe more for the 2 outer magnets).

    EDIT: If you still can't picture it imagine the left cylinder moving counter clockwise and the right cylinder moving clockwise so whatever is in between can be shot out.
     
  2. jcsd
  3. Mar 30, 2017 #2

    berkeman

    User Avatar

    Staff: Mentor

    Can you Upload a sketch?
     
  4. Mar 30, 2017 #3
    Here
    ArlBX4a.png
    http://blob:http://imgur.com/ea934414-893d-47f6-ac60-46e228ed142c [Broken]
     
    Last edited by a moderator: May 8, 2017
  5. Mar 30, 2017 #4

    davenn

    User Avatar
    Science Advisor
    Gold Member

    so you want to make a weapon ?
     
  6. Mar 30, 2017 #5

    berkeman

    User Avatar

    Staff: Mentor

    It kind of looks more like a toy to me, but I'm still not getting it...
     
  7. Mar 30, 2017 #6

    davenn

    User Avatar
    Science Advisor
    Gold Member

    OK I will let you keep an eye on it
    just going to PM you re such things
     
  8. Mar 30, 2017 #7

    berkeman

    User Avatar

    Staff: Mentor

    Welcome to the PF.

    LOL, show me the rail...?
     
    Last edited by a moderator: May 8, 2017
  9. Mar 31, 2017 #8
    What do you mean? You can understand the concept from that image alone surely
     
  10. Mar 31, 2017 #9

    berkeman

    User Avatar

    Staff: Mentor

    No, sorry. I'm not understanding what you are trying to do.

    And please don't call me Shirley.
     
  11. Mar 31, 2017 #10
    Well, like I said imagine 2 cylinders on either side of a smooth path that are being rotated using magnets, left one going counter clockwise and the right clockwise. If you put a projectile the same width as path wouldn't the 2 cylinders shoot it out. I already know the answer my real question is what would the cylinders and path have to be made from and what kind of force would the magnets need or at least what kind of speed the cylinders need to be going.
     
  12. Mar 31, 2017 #11

    berkeman

    User Avatar

    Staff: Mentor

    Rotated how using magnets? Some kind of motor arrangement? Where is the varying current flowing to generate the rotational forces?
    No. If there are magnets on the rotating cylinders and you place a ferrous ball near them at the bottom, the ball will be attracted to the magnets and accelerate upward. But as it starts to exit the path at the top, it will be pulled back by the magnets, which will slow its velocity. You may get a net velocity out of the top, but it will be less than if you switched off the magnets as the ball reached its maximum velocity before exiting the channel...
     
  13. Mar 31, 2017 #12
    The projectile would not be magnetic. The magnets are simply used to make the cylinders spin.
     
  14. Mar 31, 2017 #13

    berkeman

    User Avatar

    Staff: Mentor

    Oh, like a tennis ball launcher machine? Why not just use electric motors to spin the cylinders? They would be much more efficient.

    https://i.ytimg.com/vi/oZjx7F1doGs/hqdefault.jpg
    hqdefault.jpg
     
  15. Mar 31, 2017 #14
  16. Mar 31, 2017 #15

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    If you mean videos like this one..

    ..then you need to know it's fake.
     
  17. Mar 31, 2017 #16
    I'm not talking about that, more like this:
    jrs-wheel.png
     
  18. Mar 31, 2017 #17
    I might as well post this question in this thread: Can you have the north and south pole aligned diagonally on a cube. So instead of 1 face being north and 1 south, you'd have 1 corner north and 1 south?
     
  19. Mar 31, 2017 #18

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    That doesn't work either.

    Permanent magnets alone cannot be used as a continuous power source. Read up on conservative forces https://en.wikipedia.org/wiki/Conservative_force . In short the force between two magnets is conservative. This means that if one magnet moves relative to the other, around any shape path such as a circle, and ends up back where it started, then the net work done or produced is zero. The fan in that video or your disk above returns to the starting position (or an equivalent) at least once per revolution, therefore it is not possible for it to do any work (it can't power a lightbulb).

    However magnets can be used to store energy like a spring (eg Two magnets with their North poles together). In that case the system stores energy provided by something else (eg your hand) but it can't provide power continuously/indefinitely.
     
  20. Mar 31, 2017 #19

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    PS This and other perpetual motion machines are banned topics according to forum rules so this thread is likely to be closed.
     
  21. Mar 31, 2017 #20

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    Sure. You can make magnets virtually any shape you like.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Can magnets on a cylindrical object be used for projectiles?
Loading...