Pulley block and Simple machine

Pulley block noun - A simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope.

Simple machine and pulley block are semantically related. In some cases you can use "Simple machine" instead a noun phrase "Pulley block".

Simple machine noun - A device for overcoming resistance at one point by applying force at some other point.

Pulley block and simple machine are semantically related. Sometimes you can replace phrase "Pulley block" with "Simple machine", this phrases are similar.