simple pulley system
The simplest pulley system consists of two groups that are
identical. The upper group is the fixed one. The string goes
over the upper group’s first pulley and then comes downto
the lower group, which is moving, and wraps around the
lower group’s first pulley. Then it comes back to the upper
group and is tied to it, or it can be wrapped around a second
pulley and repeat the arrangement between the first two
pulleys.