Mechanics: Meter Stick on Fingers

PIRA Class: 1J10.30

Purpose:
Demonstrate that a balanced object will always have the center of mass between its supports. Also illustrates how the normal force on each support depends on the support's location.

Description:
Place two fingers underneath a horizontal meter stick and slowly slide your fingers together. Your fingers will always meet at the center of mass.

1. Start with your fingers symmetric about the center of the meter stick, ask students to predict where they will meet, then do the experiment.

2. Repeat, this time starting your fingers asymmetric about the center.

3. Switch to the meter stick with holes and hang additional weight on one end to change the center of mass then repeat.

4. Variations: Use one finger and a pencil (in your hand) illustrating different coefficients of friction. Use one finger and replace the other finger with a ring stand bar (finger and meter stick will move so that finger and bar meet at the CM).

PHYSICS: The normal force on the finger closer to the CM is larger than on the finger further from the CM. This leads to different friction forces between each finger and the ruler allowing the finger further from the CM to slide further/faster resulting in the fingers naturally meeting at the CM.

Equipment:
Meter stick, meter stick with holes, ring stand and cross bar (optional)

Location:
Shelf 153 (ring stand and cross bar), regular meter sticks and meter stick with holes are next to the PHYS-102 door

Extras:
A quick explanation
Discussion of the variations
Quantitative analysis