1J10.20 Metre Stick on Fingers

Concepts

Centre-of-gravity, dependence of friction on the normal force, balance of torques

Overview

A meter stick is supported on the two forefingers. The fingers are moved slowly together and end up at the center of gravity of the stick.

Details

Equipment

  • [1] Meter stick
  • [1] 200 gram weight
  • [1] plexiglas cylinder and a cork covered piece of wood
  • Optional: an 8 foot length of 2" x 2" and a 1 kg weight

Script

  1. Place the meter stick on your forefingers with one finger at 0cm and one at 100cm.
  2. Slowly move your fingers together. Your fingers will alternate between slipping and sliding along the stick and will come together at 50cm, the center of gravity.
  3. Place a 200 gram weight on one end of the meter stick.
  4. Repeat steps 1 and 2. The center of gravity has moved because of the weight and your fingers will come together on the side with the weight.
  5. Repeat steps 1 through 4 using a plexiglass cylinder and a cork covered piece of wood instead of your fingers to show this works when the coefficients of friction of the supports are different.
  6. (Optional) Repeat steps 1 through 4 above using an 8 foot length of 2" x 2" in place of the meter stick. Using a 1kg weight on the end moves the center of gravity to 70cm from the end.

 

Additional Resources

References

  • PIRA 1J10.20
  • Video Encyclopedia 04-15
  • Sutton M-50; DaR M-478; Taylor 1.23 p47; Ehrlich(1) D9 p49; Miller p16; Kutliroff 47 p106; Freier Fig 10.8 p100; Steinhaus p140

Disclaimer

  • Don't attempt this at home!

Last revised

  • 2018

Technicals

  • Assembled from lab equipment

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.