Equilibrium of Forces - SS1 Physics Lesson Note

In physics, the concept of equilibrium refers to a state in which the net force acting on an object is zero. When an object is in equilibrium, it experiences a balanced set of forces, resulting in a stable condition with no acceleration or changes in its state of motion. The equilibrium of forces can be understood through the following key points:

1. Conditions for Equilibrium:

   For an object to be in equilibrium, two conditions must be met:

• The vector sum of all external forces acting on the object must be zero. This condition is known as the equilibrium condition for forces.

The vector sum of all torques (or moments) acting on the object must be zero. This condition is known as the equilibrium condition for torques.

2. Equilibrium Condition for Forces:

The equilibrium condition for forces states that the algebraic sum of all external forces acting on an object must be zero. Mathematically, this can be expressed as:

     ΣF = 0

   Here, ΣF represents the sum of all external forces acting on the object.

3. Equilibrium Condition for Torques:

The equilibrium condition for torques states that the algebraic sum of all torques (or moments) acting on an object must be zero. Torques are rotational forces that tend to cause objects to rotate. Mathematically, this can be expressed as:

      Στ = 0

   Here, Στ represents the sum of all torques acting on the object.

4. Static Equilibrium:

When an object is in static equilibrium, it is at rest and experiences zero net force and zero net torque. This means that all the forces acting on the object balance each other out, and there is no tendency for the object to move or rotate.

5. Dynamic Equilibrium:

In dynamic equilibrium, the object is moving at a constant velocity. Although there may be non-zero forces acting on the object, the net force is zero, resulting in no acceleration. Dynamic equilibrium occurs when the applied forces and resistive forces (such as friction) balance each other.

6. Applications of Equilibrium of Forces:

   The concept of equilibrium is used in various practical applications, including:

• Structural engineering: Ensuring that buildings, bridges, and other structures are in equilibrium to maintain stability and prevent collapse.

Mechanical systems: Balancing forces in machines, pulley systems, and levers to optimize performance and prevent malfunction.

Statics and dynamics: Analysing the forces acting on objects at rest or in motion, and solving problems related to equilibrium and stability.

Understanding the equilibrium of forces is crucial for analyzing and predicting the behaviour of objects and systems. It allows us to determine the conditions under which objects remain stationary or move with a constant velocity. The principles of equilibrium form the basis for studying statics, dynamics, and mechanical systems in physics and engineering.