Block and tackle mechanical advantage explained
How rope segments multiply your lifting force, why you trade distance for force, and where real pulleys fall short of the ideal.
The core idea: sharing the load across ropes
A block and tackle threads a single rope back and forth between a fixed block and a movable block. Every segment of rope that runs up to the movable block carries a share of the weight. If four segments support the load, each one holds a quarter of it, so pulling the free end only needs to overcome that quarter. The ideal mechanical advantage is therefore just a count of those supporting segments, which is exactly what this calculator uses.
Why you trade distance for force
Energy is conserved, so a pulley cannot give you something for nothing. Cutting the required force by a factor of four means pulling four times as much rope to raise the load the same height. That is the rope pulled multiplier the tool reports. It is the same bargain a ramp or a lever makes: less force applied over a longer path, with the product, the work done, unchanged.
Converting weight into a load force
The tool asks for the load in newtons, the SI unit of force, because mechanical advantage is a force ratio. If you know the mass in kilograms, multiply by roughly 9.81 to get its weight in newtons under normal gravity. A 60 kilogram load is about 589 newtons, and a two rope system would then need around 294 newtons of effort. Keeping everything in newtons makes the effort force come out directly.
Ideal versus real pulleys
Real hardware never matches the ideal figure. Friction in the sheaves, the stiffness of the rope as it bends around each wheel, and the weight of the movable block itself all eat into the advantage. A system with an ideal advantage of 4 might deliver an effective advantage closer to 3 once losses are counted. Treat the calculator's output as the best case and add margin when specifying rope strength or a winch for a real lift.