The torque of a couple

5 minAS Level4.1.4

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can define the torque of a couple, calculate it (including when the forces act at an angle) and explain why it's the same about every point.

How hard is it turning?

A couple's resultant force is zero, so we can't measure its strength in newtons. Instead we measure how hard it turns: its torque.

Old lorries without power steering had huge steering wheels. A wider grip gives a bigger torque for the same push from each hand.

Definition

Torque of a couple

The torque of a couple is the product of one of the forces and the perpendicular distance between the lines of action of the two forces.

$\text{torque} = F \times d$

Unit: N m.

Worked example: Easy one first: a steering wheel

Each hand pushes with $15\ \text{N}$ , tangentially, on opposite sides of a steering wheel of diameter $0.40\ \text{m}$ . Find the torque.

Have a go first?

Quick check

CalculateQuestion 1 · Recall

Fill in the blanksQuestion 2 · Recall

Multiple choiceQuestion 3 · Recall

Answer the 3 questions above to continue.