Re: What is the difference between plastic bushings and metal ball bearings?

The best explanation of a ball bearing is at
 http://www.howstuffworks.com/bearing.htm
 
A bushing is just a round tube that is made out of a material that reduces 
sliding friction, like teflon or oil impregnated bronze.  The shaft 
rotates by sliding on the inside of the bushing.  The friction is higher 
than a ball bearing, where the parts contact by rolling.  A ball bearing 
is like a car rolling along a highway.  A bushing would be like dragging 
it sideways.  Of course, a bushing has lower friction than rubber on 
concrete, but you get the idea.  Bushings are inexpensive and are used 
where the amount of friction or wear is not that important, like a toy 
car.  Ball bearings are used for high speed, high side load, or long wear 
like the wheel bearings in your car.  
 
The website explains it with pictures better than I can.