I've just been wathcing the Vids concerning the yardstick. "brain teaser with a stick". Does anyone have an explination to this phenomenon?
Thanks I've just been wathcing the Vids concerning the yardstick. "brain teaser with a stick". Does anyone have an explination to this phenomenon?
Thanks @OCW Scholar - Phy…

Question

anonymous · Answer

More details?

underhill · Answer

You're referring to the yardstick teaser at the end of one of Prof. Lewin's lectures?

As Professor Lewin moved his two fingers toward each other, those two fingers were the only supports the yardstick had.  The yardstick had to choose which finger to slide over - it always chose the finger bearing the least weight, since there the coefficient of static friction was least.

Of course, soon that finger was no longer the easiest to slide over when the majority of the yardstick's weight was transferred to that finger - which happened as more of the yardstick slid past that finger.  So the yardstick would stop sliding over that finger and begin to slide over the other finger, and so on until the two fingers met in the middle, with an equal weight on each.