A construction worker needs to lift a heavy metal beam using a lever but has a limited length of plank. Which adjustment would allow the worker to lift the beam with the least effort if the position of the fulcrum can be changed but the plank length remains constant?
Move the fulcrum closer to the beam
A lever is one of the six classical simple machines, and here the crowbar-and-plank arrangement acts as a lever that multiplies the worker's effort. Its effectiveness is measured by the Mechanical Advantage (MA):
MA = Effort arm ÷ Load arm, where the effort arm is the distance from the fulcrum to the point where the worker pushes, and the load arm is the distance from the fulcrum to the beam. The higher the MA, the smaller the effort needed to balance or lift a given load, because at balance Effort × Effort arm = Load × Load arm.
Since the plank length is fixed, the fulcrum's position decides how that fixed length is split between the two arms. To lift the heavy beam with the least effort, the worker wants the largest possible MA, which means the longest possible effort arm and the shortest possible load arm. Moving the fulcrum closer to the beam (the load) does exactly this: it shrinks the load arm and enlarges the effort arm, driving the MA up. This is precisely why a crowbar is jammed with its pivot as close as possible to the object being pried.
Consider the wrong choices. Placing the fulcrum at the centre makes the two arms equal, so MA = 1 and there is no force multiplication at all. Keeping the fulcrum fixed at any arbitrary point gives no guaranteed advantage and does not answer how to minimise effort. Moving the fulcrum closer to the worker does the opposite of what is wanted — it lengthens the load arm and shortens the effort arm, reducing MA below 1 and demanding more effort than the beam's own weight. Hence the correct adjustment is to move the fulcrum closer to the beam.
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