Pulley.
What is a pulley?
A pulley is a wheel with a groove or hollow cut in its edge.
What is the groove for?
The groove is cut so that a rope may move over the wheel without slipping off.
Fig. 55.
In [Fig. 55], where is the power applied?
The power is applied to one end of the rope by the hand.
Where is the weight?
The weight is attached to the other end of the rope.
When the power and the weight are equal, what do they do?
They balance each other, and neither of them will move.
When the power is greater than the weight, what takes place?
The weight is then lifted up.
Of what use is the single pulley?
The single pulley is used for hoisting flags to the top of high poles, for raising sails to the topmasts of vessels, and for raising weights to the upper stories of mills and factories.
How many pulleys are needed, when a horse is to raise the weight?
When a horse is to raise the weight, two pulleys are needed, as may be seen in [Fig. 56].
Fig. 56.
To what use do farmers apply the pulley?
They arrange the pulleys so as to lift the hay into their barns, by means of a horse; thus saving themselves much hard labor.