Moments — A-Level Mathematics Revision

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What is Moments?

Moments at A-Level involve the turning effect of a force. You will learn to calculate moments, and apply the principle of moments to solve problems involving equilibrium of rigid bodies, such as beams and ladders.

Board notes: All A-Level Maths boards (AQA, Edexcel, OCR) cover moments in their mechanics content. The complexity of the problems, such as those involving non-uniform rods and ladders, is similar across the boards.

Worked example

Common mistakes

• 1Confusing the moment of a force with the force itself. A moment is a turning effect, calculated as the force multiplied by the perpendicular distance from the pivot.
• 2Making errors in taking moments about a pivot. It is crucial to correctly identify the pivot and the perpendicular distances of all forces from the pivot.
• 3Forgetting to include all forces when considering the equilibrium of a rigid body. This includes reaction forces at supports and any frictional forces.

Moments exam questions

Exam-style questions for Moments with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is the principle of moments?

  The principle of moments states that for an object to be in rotational equilibrium, the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about the same point.

• How do you solve problems involving a ladder leaning against a wall?

  When a ladder is leaning against a wall, you need to consider both the rotational equilibrium (by taking moments) and the translational equilibrium (by resolving forces horizontally and vertically). You also need to consider the frictional forces at the base of the ladder and at the wall.