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How to Build a Compound Machine in the Third Grade

A compound machine is a combination of simple machines: screws, wheel and axle, pulley, wedge, lever and inclined plane. To build a compound machine, you need to know what the machine is supposed to do and what combination of simple machines you're going to put together to achieve it. One of the simplest designs uses a number of pulleys and a rope. If you have that, then you're ready to go.

Things You'll Need

  • Plastic pulleys (2)
  • Nylon string
  • Support
  • Screw in hook
  • Weight
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Instructions

    • 1

      Find a hook in a door frame or a ceiling to hang your pulley from. To create a block and tackle, a simple compound machine, you need to be able to suspend one of the pulleys from a high place.

    • 2

      Hang the first pulley from your high place. Attach the weight to the second pulley. Each of your pulleys should have hooks hanging from the top and bottom, and you need to use these hooks to suspend the top pulley and to hang the weight from the bottom pulley.

    • 3

      Tie your nylon line to the bottom hook of the top pulley. Run the line through the bottom pulley that's attached to the weight, and then run the line up through the top pulley. Grasp the end of the nylon line and pull. The two pulleys will work in concert, making the weight 50 percent less than it was. This is a basic block and tackle assembly, and the more pulleys you add the easier it is to lift objects.

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