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.
Inclined Plane.
When one end of a plank is raised up, while the other end remains on the floor, is its surface level?
No; its surface is not level.
What may the surface of the plank be called?