4.4.1—Forces
- Syllabus
- 9709–2028–2029
- Objective
- 4.4.1
- Level
- A2
Newton’s second law applies to the resultant force on the chosen body
For a body of mass m, ΣF=ma. The acceleration points in the direction of the resultant, not necessarily in the direction of the largest individual force.
Draw a free-body diagram, resolve along convenient axes and include friction, tension, weight and reactions only when they act on the chosen body.
A 5 kg block with 20 N right and 8 N left has resultant 12 N right and acceleration 2.4 m s⁻² right.
Action–reaction pairs belong to different bodies and cannot be cancelled inside one body’s force equation.
ConceptA-Level CAIE Mathematics A2