|A pulley is made
from a wheel and a rope. It is used to make lifting
easier. A single pulley changes the direction of the
lifting force. For example, if you are lifting a heavy
object with a single pulley anchored to the ceiling, you
can pull down on the rope to lift the object instead of
pushing up. The same amount of effort is needed as
without a pulley, but it feels easier because you are
pulling down. If you add a second pulley, the amount of
effort to lift the heavy object is much less -- half as
much. However, you will have to pull the rope further. A
double pulley can help you to lift objects you could
never lift without it.
Pulleys are also used on elevators. Remember the elevator in the book? If you would like to build an elevator using K'nex, click here . Pulleys are also used on cranes to hoist things up. Can you think of other pulleys you have seen? Look at the pictures below to see some pulleys I found. To see animated pulleys, click here .