A book rests on a shelf attached to a wall. The book is not moving. Explain why the book remains stationary, referring to the forces acting on it.

Eduqas GCSE Physics — 3.1 Forces and their interactions · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The book’s weight, a downward gravitational force, acts on it. The shelf exerts an upward normal contact force on the book. These two forces are equal in magnitude and opposite in direction, so they balance each other. With the resultant force zero, the book remains stationary.

Examiner tips

  • Use the word ‘exert’ for the normal force; mention weight and normal force explicitly.
  • Show the forces are equal and opposite to justify balance.
  • State that a zero resultant means no acceleration (book stationary).

Common mistakes

  • Confusing the normal force with friction; forgetting to mention weight.
  • Saying the forces are ‘balanced’ without stating they are equal and opposite.
  • Writing that the book is ‘at rest’ without linking it to zero resultant force.

Mark scheme (4 marks)

  1. Weight (gravitational force) acts downward on the book
  2. The shelf exerts a normal contact force upward on the book
  3. The two forces are equal in size (and opposite in direction)
  4. The forces are balanced, so the resultant force is zero, meaning the book remains stationary

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