GCSE Physics · Edexcel 1PH0 · Topic 9A
Resultant forces and vector diagrams
Key points
- Add forces in the same direction; subtract forces in opposite directions to find the resultant force.
- If the resultant force is zero, the forces are balanced and the object is in equilibrium (stationary or moving at constant velocity).
- Free-body diagrams show each force on one object as an arrow with size and direction.
- For two forces at right angles, use a scale drawing or Pythagoras to find the resultant's size, and measure its direction.
- Resolving splits one force into two perpendicular components, e.g. a force on a slope into parts along and at right angles to the slope (higher tier).
- In equilibrium, the forces drawn tip-to-tail make a closed triangle (higher tier).
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The resultant force tells you what all the forces on an object add up to. If you can find it, you can predict whether the object will stay still, keep moving steadily, or accelerate.
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