Forces in Action: Understanding Forces in Equilibrium

Different Types of Forces

In mechanics, several types of forces act on objects. These include:

• Gravitational force: The force of attraction between any two masses due to gravity
• Electromagnetic force: The force between charged particles or between a charged particle and a magnetic field
• Normal force: The contact force exerted by a surface on an object
• Friction force: The resistive force that opposes relative motion between two surfaces
• Tension force: The pulling force transmitted by a string, cable, or rope
• Elastic force: The restoring force exerted by a deformed elastic material

Equilibrium Conditions

An object is in equilibrium when the vector sum of all forces acting on it is zero. For an object to be in equilibrium, two conditions must be satisfied:

1. The vector sum of all forces must equal zero: ΣF = 0
2. The net torque or moment about any point must equal zero: Στ = 0

Worked Example: Force Analysis on an Inclined Plane

Consider an object of mass m on an inclined plane making an angle θ with the horizontal.

1. Draw a free-body diagram showing all forces acting on the object
2. Resolve the forces into components parallel and perpendicular to the plane
3. Apply ΣF = 0 and Στ = 0 to find the acceleration and reaction forces

Concepts in Force Analysis

• Force diagrams: Graphical representations showing all forces acting on an object
• Resolution of forces: Breaking a force into components along specified axes
• Moments and torque: The tendency of a force to cause rotational motion about a pivot
• Centre of mass: The point where the entire mass of an object can be considered concentrated
• Principle of moments: The sum of clockwise and anticlockwise moments about a point must be equal for equilibrium