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Having trouble constructing a device that will make a sound at 5 second intervals

  1. Mar 24, 2012 #1
    My semester project is to create a device that will make a sound at 5,10 15, and 20 seconds exactly using only gravitational energy.
    -My initial design used two rotating axles with two gears through them and a chain. It would begin by me dropping a weight attached to one of the axles making it rotate exactly five times and hitting something to make a sound. I would also use the inside mechanism of a tape measurer to somehow make the axle retract back into place at exactly five turns and make another sound and so forth.... However this is a lot easier said than done.

    Any suggestions to this idea would be helpful or something totally new would also be great.
  2. jcsd
  3. Mar 24, 2012 #2
    The weight will not return to the starting point without some external energy input. (Gravity is not an energy source.) In essence, you're describing a weight-driven mechanical clock -- the weight is reset by hand.
  4. Mar 24, 2012 #3
    Thats the problem i'm facing, for somehow to reset itself or wind itself up
  5. Mar 24, 2012 #4


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    Welcome to Physics Forums! Perpetual Motion machines and "free energy" devices are strictly prohibited here. If what you are asking about amount to one of these, your post will be locked my our monitors.

    In the meantime, if you discover how to get your machine to "wind itself up" do NOT post it here in public. Send me a private message with all the details. Bobbywhy
  6. Mar 25, 2012 #5


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    And incidentally, everywhere else in the universe that the laws of thermodynamics apply. :smile:


    But seriously, how many times must the bell ring? Only 5? Or does it need to ring for an arbitrarily long time? You can still use a system that winds down only once, just ensure it rings the bell as many times as necessary. Do you know how a grandfather clock works? You only have to reset its mechanism every few months.
  7. Mar 25, 2012 #6
    5,10,15,and at 20 seconds so four times. If I use a system that winds down once I wouldnt really know how to make it make the sound four times, I guess that's how the grandfather clock would work
  8. Mar 25, 2012 #7


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    albert1992, Thanks for the information in post #6 above. It always helps to communicate the complete "specifications" so we may better assist you with suggestions.

    Consider a disc that is driven by your gravity weight so as to rotate once every 20 seconds. Insert protruding pegs at the 90, 180, 270, and 360 degree points near the circumference of the disc. These pegs ring a bell mounted near the disc as they pass by. Four complete revolutions will suffice.
  9. Mar 25, 2012 #8
    Well I used a similar concept but I had trouble controlling the speed of the disc I was using. Getting the timing right was the challenge.
  10. Mar 25, 2012 #9


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    "Getting the timing right" was the objective of clockmakers for centuries. The "escapement" seems to have been the solution. It acts just like a speed governor.
  11. Mar 25, 2012 #10

    jim hardy

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    Look at old clock chimes.
    For speed control they use a paddlewheel that churns the air. It's geared to the cammed wheel thats operating the striker but turns much faster and wind resistance being ω^2 you can get substantial gain.
    Interesting feedback mechanism, it's used on lawnmower governors too..
  12. Mar 25, 2012 #11


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    Staff: Mentor

    A heavy pendulum. As it swings by, a stick protruding from it delivers a glancing blow to a bell or tin can. :smile:
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