How does pulleys make things easier?

Answer 1

A simple pulley as on a flagpole does avoid climbing the pole, but the effort to raise the flag is still the same. In fact there will be a small loss of energy due to friction in the pulley.

You have to have at least two pulleys, before any effort is reduced.

But though the momentary effort is reduced, since you are raising a mass against the gravity, the total energy consumed will be the same.

Assume a rope passing over one pulley which is fastened to the roof, then dropping down round another pulley, before being fastened to the roof again. So the rope forms in total an 'S', and between the lower pulley and the roof it forms an 'U' shape.

Assume your target mass is fastened to a hook on the lower pulley. Draw this.

As you pull on the free end of the rope, you will have to pull two lengths (metres or feet) of rope down for each length that your target mass rises.

In the overall scheme of things, you'll have to put in the same amount of work needed to raise your target mass to the roof. But the momentary effort will be halved. And you'll have moved twice as much rope as the distance your target mass rises. You have a 'mechanical advantage' of two times.

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A single pulley, or two pulleys, does not magnify force, but does change the direction of the force. Three or more pulleys properly arranged (for example, in a block and tackle arrangement) can not only change the direction of a force but also magnify the force. For example, using a block and tackle hoist will allow you to lift hundreds of pounds while exerting much less force. The trade-off is that you must exert the smaller force over a longer period, which evens things out.