Torque and mechanical advantage — Engineering, 14–17 years
Torque explains how a force makes something turn, and why a longer handle can make the same job easier.
What torque means
A force can push an object straight, but it can also make it turn. Torque measures that turning effect: the same force produces more torque when it acts farther from the pivot or at a right angle.
The problem of turning things
Bolts, wheels and doors may resist turning even when you push hard. Engineers needed a way to compare pushes at different distances, so torque helps them choose handles, gears and motors without relying on guesswork.
Opening a tight bolt
You push a spanner with 40 newtons at a point 0.25 metres from the bolt. Torque equals force times perpendicular distance: 40 × 0.25 = 10 newton-metres. A 0.50-metre spanner with the same push would give 20 newton-metres.
The distance is not always enough
A common mistake is to multiply by the whole length of a handle, even when the force is slanted. This is understandable because the handle looks like the important distance, but torque uses the shortest distance from the pivot to the force’s line of action.
Where torque is used
Bicycle gears trade turning force for speed: a low gear helps when climbing, while a high gear suits faster riding. Engineers use the same idea in drills, car transmissions, cranes and robotic joints, where motors must turn loads in a controlled way.
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