3.4.1.1
Forces in equilibrium form a closed vector triangle
Scalars & Vectors — AQA A-Level Physics
Key Definition
Equilibrium — An object is in equilibrium when the resultant force on it is zero. It is either at rest or moving at constant velocity.
- Coplanar forces in equilibriumAn object is in equilibrium when the resultant force on it is zero. The object is either stationary or moving at constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. are represented by a closed vector triangle (or polygon for more than three forces).
- Arrange the force vectors head-to-tail: if they form a closed path, the forces are in equilibriumAn object is in equilibrium when the resultant force on it is zero. The object is either stationary or moving at constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹...
- The most common forces are weight, normal reaction, tension and friction.
- If the triangle does not close, there is a resultant force and the object is not in equilibriumAn object is in equilibrium when the resultant force on it is zero. The object is either stationary or moving at constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹...
Common Mistake
MEDIUM
Students often: Drawing force arrows all starting from the same point instead of head-to-tail.
Instead: For a closed vector triangle, each vector must start where the previous one ends. The fact that the path closes shows the resultant is zero.
Instead: For a closed vector triangle, each vector must start where the previous one ends. The fact that the path closes shows the resultant is zero.
Related:Kinematics