3.4.1.2
Centre of gravity equals centre of mass in a uniform gravitational field
Moments, Couples & Equilibrium — AQA A-Level Physics
- Centre of mass depends only on mass distribution, not on the gravitational fieldA region of space in which a mass experiences a gravitational force..
- Centre of gravityThe single point at which the entire weight of an object can be considered to act. depends on the gravitational fieldA region of space in which a mass experiences a gravitational force. because $weight = mass times g$.
- Near the Earth's surface, where g is effectively uniform, centre of mass and centre of gravityThe single point at which the entire weight of an object can be considered to act. coincide.
- In a non-uniform gravitational fieldA region of space in which a mass experiences a gravitational force. (e.g. an object between Earth and Moon), the centre of gravityThe single point at which the entire weight of an object can be considered to act. shifts towards the stronger field.
Examiner Tips and Tricks
At A-Level, you can treat centre of mass and centre of gravity as the same point unless the question explicitly involves a non-uniform gravitational field.
Related:Newton's Laws