Kinotics

⚖️ EQUILIBRIUM IN PHYSICS | JEE & NEET

Equilibrium is one of the most important concepts in mechanics. A body is said to be in equilibrium when the resultant (net) force and resultant torque acting on it become zero. In this condition, the body has no linear or angular acceleration.

Conditions of equilibrium:

∑F = 0
∑τ = 0

There are two major types of equilibrium:

1. Static Equilibrium
The body remains at rest.
Examples: Book on a table, hanging lamp, balanced seesaw.

2. Dynamic Equilibrium
The body moves with constant velocity because acceleration is zero.
Examples: Car moving at constant speed, elevator moving uniformly upward.

First Condition of Equilibrium (Translational Equilibrium):

∑Fx = 0
∑Fy = 0

Second Condition of Equilibrium (Rotational Equilibrium):

∑τ = 0

Types based on stability:

• Stable Equilibrium → Body returns to original position after displacement.
• Unstable Equilibrium → Body moves farther away after displacement.
• Neutral Equilibrium → Body stays in the new position after displacement.

Important JEE & NEET Points:

• Equilibrium does not always mean rest.
• Zero acceleration can still mean constant velocity motion.
• For rigid body equilibrium, both force balance and torque balance are necessary.
• In equilibrium:

a = 0
α = 0

This topic is highly important for Laws of Motion, Rotational Mechanics, Center of Mass, and Mechanics problem solving in JEE Main, JEE Advanced, and NEET Physics.