The pulley definition

I think this is the pulley of the familiar things, machinery, especially with its architecture, carry heavy things, all must depend on the pulley afford that heavy products, then slowly rising reaches the specified purpose, pulley groove, there is a peripheral to the rotation axis. The central axis rotation have groove around the disc and across the flexible disc (rope, tape, rope, chain which is composed of) around the center axis can be simple mechanical called pulley if auto tensioner pulley, DongHuaLun, diagram, etc.
Why would people use pulley to transport, rather than to lift, after using the pulley and it can give people a lot of effort. Good reduced human labor resources.