Class 11 Physics Rotational Motion Centre of Gravity

Centre of Gravity

  • The centre of gravity of a body is that point where the total gravitational torque on the body is zero.

  • The centre of gravity of the body coincides with the centre of mass in uniform gravity or gravity-free space.
  • If g varies from part to part of the body, then the centre of gravity and centre of mass will not coincide.


Example: A car weighs 1800 kg. The distance between its front and back axles is 1.8 m. Its centre of gravity is 1.05 m behind the front axle. Determine the force exerted by the level ground on each front wheel and each back wheel.


Solution:  Equating forces in vertical direction (translational equilibrium) -  Rf + Rb = mg  - (1)

Equating the torques at CG (Rotational equilibrium) -  Rf (1.05) = Rb (1.8-1.05)  - (2)
Note: We have chosen CG as the torque of gravitational forces is zero at this point.
Solving Eqn (1)&(2)  we can find Rf & Rb .

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