M1.4.6 Moments and equilibrium
This resource illustrates the conditions for a rigid body to be in equilibrium - that the resultant force in any direction must be zero, and the sum od the moments about any point must be zero.
It shows a simple case of three parallel forces, orthogonal to a rod.
Use the blue stepper to show the conditions. In the final stage, moments are taken about point A, since this allows the force at A to be ignored, simplifying the equation.
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