URPOSE: This demonstration illustrates the following concepts: (1) balance of
torques, (2) friction and the
normal force, (3) finding the center of gravity.
DESCRIPTION: Balance the meter stick on your two index fingers, with one finger
initially at one end and the
other finger about one-quarter of the way from the other end. Slide your fingers together
(moving either one or the
other or both). You r fingers will always end up together directly under the center of
mass.
Try different starting points. Try adding a 100 gram weight onto either end. Try
greasing your
finger. It always works. Ask your students what they think will happen before doing the
original experiment. Ask
them again after ad ding a weight to one end.
EQUIPMENT: Meter stick. Masses optional.
SETUP NOTES: None.