Pulleys aren't that common on bicycles, pretty much only bikes with external gears have them. They're used in the rear derailer to let the chain change direction so that the derailer can take up the slack that comes from changing gears.
Some ladies/mixte frames use a pulley up by the seatpost to change the pull direction of the brake wire. Yet some bikes use a pulley to get the right pull direction for the front derailer.
Sort of. If it's an externally geared bike it will have both a guide pulley and a tension pulley to deal with the chain slack
The bicycle is not a simple machine, there are too many interacting moving parts.
pulley
pulley
pulley
lever at crank, connected by chain to lever at rear wheel
You can head on down to your local bicycle shop to find a selection of bicycle frames. It might be better to see them in person than to purchase it online.
gears and wheel and axle
The chain is wrapped around a cogwheel, which could be described as a pulley.
Things that might cause a pulley to wobble: The pulley is bent. The shaft the pulley is on is bent. The pulley is mounted crooked.
There are websites that compare prices, for example Nextag, BestCovery and Yahoo! Shopping. On these websites you can look up the bicycle trainer that you want to buy and find the store that has the best deal for it.
It should run off the sprocket(at the rear wheel), over the top pulley, down the frontside of the top pulley, then to the rear and underside of the bottom pulley before heading towards the cranks/chainrings.
In the bicycle shop in Goldenrod city