Which pulley setup would decrease the amount of effort force needed to lift an object?

Answer 1

One moving pulley attached to the object being lifted, but one may not be enough for very heavy loads.

That would depend on what lifting devices you had on hand, and how heavy the load is. If the load is say 300 lbs. and you only have one man available to do the lifting; then you would not use a simple single pulley because you would be lifting the full 300 lbs. as dead weight. If you elect to use a Gun Tackle you would gain a mechanical advantage of 2. Thus dividing the dead weight load by a factor of 2, which would mean that the man hauling on the running end of the rope would be experiencing a load of 150 lbs.

On the other hand if you were to use a Luff then the M.A. is 3; thus reducing the load to 100 lbs.

A Double Tackle gives you an M.A. of 4; reducing your load weight to 75 lbs.

A Gyn Tackle (1 triple sheave block and 1 double sheave block) gives you an M.A. of 5; the man on the pulling end of the system is now only experiencing a pull of 60 lbs.

A Threefold Purchase (2 triple sheave blocks) gets an M.A. of 6; thus 50 lbs.

But for all practical purposes, you would not elect to dig out a Threefold Purchase for such a small load to be shifted. A more efficient method would be to use either a Luff or a Double tackle. Keep in mind that as you reduce the load weight on the hauling end, you increase the amount of line you have to pull through the tackle. I.e. if you use a simple pulley, for every foot you lift the off the deck, 1 foot of line passes through the pulley. Conversely, if you use a Double Tackle (Twofold Purchase) for every one foot lifted off the deck you must pull 4 feet of line through the sheaves.

Answer 2

A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.

Answer 3

see: block and tackle

Answer 4

block and tackle

Answer 5

It needs at least one movable pulley,