# 4.1.4 Conditions for Equilibrium

### Equilibrium

• A system is in equilibrium when all the forces are balanced. This means:
• There is no resultant force
• There is no resultant torque
• An object in equilibrium will therefore remain at rest, or at a constant velocity, and not rotate
• The system is in an equilibrium state when applying the principle of moments (see The Principle of Moments)

### Coplanar Forces in Equilibrium

• Coplanar forces can be represented by vector triangles
• In equilibrium, these are closed vector triangles. The vectors, when joined together, form a closed path
• The most common forces on objects are
• Weight
• Normal reaction force
• Tension (from cords and strings)
• Friction
• The forces on a body in equilibrium are demonstrated below:

#### Exam Tip

The diagrams in exam questions about this topic tend to be drawn to scale, so make sure you have a ruler handy! ### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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