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tiny-tim
#2
Feb11-12, 03:44 AM
Sci Advisor
HW Helper
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P: 26,148
hi sacher! welcome to pf!

let's start with the simplest case a wheel with one cylindrical hole across a diameter, and a rod we can slide along it
with the rod horizontal and with the brake on, we slide the bar to the left, then we release the brake

the wheel turns 180, until the rod is at the right

now we apply the brake again, slide the rod through, release the brake, and so ad infinitem
however

i] this assumes no friction in practice, because of friction, the rod won't quite return to horizontal

ii] even if we add more rods (at different angles), pushing them out when they're exactly horizontal, the same thing will happen: the wheel will turn to the point where the centre of mass is at the original height

(and if we push a rod out when it's above the horizontal, then we're supplying energy by doing so, aren't we? )