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GCSE Physics · key term
The straight line through a force in the direction in which that force acts.
Used by AQA, Edexcel and OCR
Paper 2
An imaginary straight line extending in the direction in which a force acts.
Revise: Introduction to Moments and Balanced SystemsWhether a force turns an object depends on both the size of the force and where its line of action lies relative to the pivot. The line of action is an imaginary straight line in the direction of the force. A force directed through the pivot has no turning effect about that pivot.
Specification 9.7P · Paper 2
The straight line along which a force acts, extended if necessary.
Revise: Moment EquationImagine extending an arrow showing the force into a straight line of action. Measure the shortest distance from the pivot to this line, at right angles to it. This is the distance normal to the direction of the force.
Paper 1, Paper 2
Revise: Work Done and PowerIn physics, work is done when a force causes an object to move along the force's line of action. Work done is not an extra substance possessed by the object: it describes an energy transfer caused by the force.
Use the perpendicular distance from the pivot to the force's line of action—not automatically the length along the object.
A force whose line of action passes through the pivot has zero perpendicular distance and therefore produces no moment about that pivot.
Mark the pivot, extend the force’s line of action if necessary, then use the perpendicular distance from the pivot to that line.
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