Forces in equilibrium
Resolve into perpendicular components; resultant = 0.
Y12 Mechanics. For a body in equilibrium: sum of horizontal forces = 0 AND sum of vertical forces = 0. Resolve forces along chosen perpendicular axes.
Worked examples
Object on slope at angle θ: weight component down the slope = mg sinθ; normal reaction = mg cosθ.
Three-force equilibrium: forces form a closed triangle.
Lami's theorem: F1/sinα = F2/sinβ = F3/sinγ (for three concurrent forces).
Frequently asked questions
Choosing axes?
Pick axes that simplify resolution. On an incline, parallel and perpendicular to the slope.
Limiting equilibrium with friction?
Friction at its maximum: F = μR.