The Physics
Hypertextbook
Opus in profectus

# Equilibrium

## Summary

• Statics is the branch of mechanics dealing with forces acting on an object at rest.
• Static Equilibrium (Point Bodies)
• A point body is in static equilibrium when the net force on it is zero.
• A point body in static equilibrium will not accelerate.
It will remain at rest or continue moving with a constant velocity.
• 2 Forces in Equilibrium
• Two forces are in equilibrium if they are
• equal (have equal magnitudes) and
• opposite (180° apart).
• 3 Forces in Equilibrium
• Resultant-Equilibrant
• Select 2 forces and find their resultant.
• The remaining force is called an equilibrant if it is equal and opposite the resultant.
• Triangle of Forces
• Three forces are in equilibrium if they can be arranged to form a triangle.
• N Forces in Equilibrium
• Polygon of Forces
• Three or more forces are in equilibrium if they can be arranged to form a polygon.
• Components
• Resolve all forces into components in some convenient coordinate system.
• Combine the components along each axis.
(Add the components parallel to the axis and
subtract the components anti-parallel to the axis.)
• If the resultant along each axis is zero the object is in equilibrium.
• No Net Force in Any Direction
 ∑F = 0 ⇒ ⎧⎨⎩ ∑F−x = ∑F+x ∑F−y = ∑F+y ∑F−z = ∑F+z