A mechanic uses a long crowbar to lift a heavy rock. Explain why using a longer crowbar makes it easier to lift the rock, and describe how the crowbar acts as a lever in this situation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A crowbar is a straight metal bar used as a lever. The mechanic places one end of the crowbar under the rock and rests the bar on a small stone (the pivot). They push down on the other end to lift the rock.
Model answer (4 marks)
A longer crowbar increases the perpendicular distance from the pivot to the point where the force is applied. The moment (turning effect) is the product of force and this distance, so a larger distance gives a larger moment for the same force. A larger moment means the rock can be lifted with less effort force. The crowbar is a lever: the small stone is the fulcrum, the mechanic’s effort force is applied on one side and the rock is the load on the other side, so a small downward force produces a large upward force.
Examiner tips
- Mention the moment equation (M=F×d) and that d is larger for a longer bar.
- Explain the lever as a first‑class lever with the fulcrum between effort and load.
Common mistakes
- Confusing the effort force with the load force.
- Saying the rock is the effort instead of the load.
- Ignoring the role of the pivot/fulcrum.
Mark scheme (4 marks)
- The moment (turning effect) depends on the perpendicular distance from the pivot to the force
- A longer crowbar increases the perpendicular distance from the pivot to where the force is applied
- A larger moment (turning effect) is produced for the same applied force, so less force is needed to produce the same moment
- The crowbar acts as a lever with the small stone as the pivot; a small downward effort force on one side produces a large upward force (load) on the other side
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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