Class 11 Physics Rotational Motion Equilibrium of Rigid Body

Equilibrium of Rigid Body

  • A force changes the translational state of the motion of the rigid body, i.e. it changes its total linear momentum.
  • A torque changes the rotational state of motion of the rigid body, i.e. it changes the total angular momentum of the body


Note: Unless stated otherwise, we shall deal with only external forces and torques.


  • A rigid body is said to be in mechanical equilibrium, if both its linear momentum and angular momentum are not changing with time. This means
  • Total force should be zero => Translational Equilibrium
  • Total torque should be zero => Rotational Equilibrium



  • A pair of equal and opposite forces with different lines of action is known as a couple or torque. A couple produces rotation without translation.


  • When you open the lid of a jar , you apply couple on it

  • An ideal lever is essentially a light rod pivoted at a point along its length. This point is called the fulcrum
  • The lever is a system in mechanical equilibrium.

  • Mechanical advantage greater than one means that a small effort can be used to lift a large load.


Share these Notes with your friends  

< Prev Next >

You can check our 5-step learning process