Torque

Torque measures a force's tendency to rotate an object about some axis or pivot, the way force measures its tendency to accelerate it in a straight line. It is the cross product of the lever arm (the vector from the pivot to where the force is applied) and the force itself, so torque depends on something a plain force doesn't need to specify: where the force is applied relative to the pivot.

That distance term is the whole reason a wrench has a long handle. The same push applied farther from the bolt produces more torque, which is why a longer wrench (or a cheater bar slid over the handle) loosens a stuck fastener that a short one can't budge, with no change in the force a person actually applies. A see-saw balances when the torques on each side are equal, which is why a lighter person sitting farther from the pivot can balance a heavier one closer in — mass alone doesn't decide balance, mass times distance does.

Torque is easy to confuse with work, since both share units that reduce to the same dimensions (force times distance) and are colloquially both called "how hard something is turning." They are not the same quantity: work requires the point of application to actually move through the force's direction, while a torque can be applied indefinitely to something that never rotates — a wrench straining against a bolt that doesn't budge does zero work despite considerable torque, which is exactly why holding a heavy object at arm's length tires the shoulder even though nothing is being lifted higher.