1G10.40 Atwood's Machine with Two Pulleys


Forces, tension


Two masses pull a scale in different directions to measure the tension in the string. One mass can be detached and the string held in hand to simulate the string being attached to a wall.



  • [2] Lab stand
  • [2] 90-degree clamp
  • [2] Pulley
  • [1] 20-N display scale
  • [2] Steel brick
  • [2] 1-kg mass
  • [2] String with hook

Classroom Assembly

  1. Place lab stands each with a steel brick on the base.
  2. Clamp a pulley to each stand.

Important Notes

  • The string may slip out of the pulleys. The string should not be under tension for longer than necessary to do the demo.


  1. Hang a mass on the loop side of a string.
  2. Lay the string over a pulley and hook it to the scale.
  3. Hook the other string to the other side of the scale and lay it over the other pulley.
  4. Hang the other mass on the loop side of the other string.


Additional Resources


  • PIRA 1G10.40


  • Don't attempt this at home!

Last revised

  • 2017


Related AV

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.