When you move the fulcrum of a lever, you also change the mechanical advantage of the lever. The mechanical advantage is the ratio of the output force (the force you are trying to lift) to the input force (the force you apply). By adjusting the position of the fulcrum, you can increase or decrease the distances from the fulcrum to the points where the forces are applied. This, in turn, affects how much force you need to exert to lift a given load, allowing you to lift heavier loads with less effort if the fulcrum is positioned correctly.
In a lever when you move the fulcrum you also change this.
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