Conditions for equilibrium of a rigid body (ΣF = 0, Στ = 0)
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ΣF = 0, Στ = 0
What each symbol means
| Symbol | What it stands for |
|---|---|
| ΣF | Vector sum of all external forces (= 0 for equilibrium) |
| Στ | Vector sum of all torques about any point (= 0 for equilibrium) |
When to use this
Both conditions must hold simultaneously. ΣF = 0 → translational equilibrium (no linear acceleration). Στ = 0 → rotational equilibrium (no angular acceleration). Torque reference point can be chosen freely.