What is the difference between center of gravity and center of mass?

1 Answer
Aug 11, 2017

See below...


An unconstrained object (no axle or pivot) on which there is no net force will rotate about a point called the center of mass.

  • The center of mass remains motionless while every other point on the object undergoes circular motion around it.
  • The center of mass is the mass-weighted center of the object.
  • The distribution of an object's mass is balanced around its center of mass.

The center of gravity is the point at which the resultant torque due to gravity disappears.

  • Gravity acts on every particle in the object, exerting a downward force of magnitude #m_ig# on a particle #"i"#.
  • The gravitational torque is found by treating the object as if all its mass were concentrated at the center of mass .
  • The point at which gravity acts is called the center of gravity
  • The magnitude of the gravitational torque on a particle is #abs(tau)=m_igd_i# where #d_i# is the moment arm
  • An object will balance on a pivot only if the center of mass is directly above the pivot point. Otherwise, the gravitational torque will cause the object to rotate.

#:.# As long as gravity is uniform over the object (always true for objects on Earth), there is no difference between the center of gravity and the center of mass.