1. Dec 30, 2009

### Stalker23

Anyone know why the big wheele spins counter clockwise in thsi video?

Can anyone draw me a free body diagram of whats going on when the ruler is pulled to the right?

thankyou

Last edited by a moderator: Sep 25, 2014
2. Dec 31, 2009

### tiny-tim

Hi Stalker23!

Free body diagrams are irrelevant, this isn't a forces problem at all, it's a piece of machinery in which moving one part automatically moves all the other parts.

Concentrate on the speed of the rims of the wheels (and remember that the cotton-reel has two rims, one in contact with the table, and one with half the diameter in contact with the big wheel).

3. Dec 31, 2009

### Stalker23

hmmm. well what i cant figure out is why the wheel spins the opposite direction. The way i was gunna prove this to myself was through a free body diagram. but when i draw it the forces i get dont make sense. Just considering hte forces between the ruler and the big wheele, i get the frictional force on the wheele to point to the right...meaning the wheele should spin to the right?

allthough if i look at the bottom two wheels, there frictional force is to the right, but causes a pos moment about the center of the big wheel. I guess those forces are larger than those between the ruler and the wheele?

4. Dec 31, 2009

### tiny-tim

Forget forces. Forget friction.

Imagine the wheels are cogs, with the same distance between teeth on all wheels.

When the cart moves at speed v, what is the speed of the teeth on the big wheel?