This is the explanation given by Wonkee Donkee’s old Physics teacher to explain the relationship between leverage and length.
Picture a typical door handle.
This functions as a lever.
Trying to push the handle down becomes harder the closer you move your finger to the pivoting mechanism (the point known in physics as the fulcrum)…
…and easier the further you move your finger away from it.
This principle is known as the law of the lever, and explains how the distance between the point of input (your hand) and the point of output (the opening mechanism) affects the amount of force required by the user.
Using the same principle: the longer the bar you use, the less force you will need to put in when levering heavy objects.