Centre of Mass

Centre of Mass

Definition
The centre of mass (also called centre of gravity) is the point where the whole weight of the body appears to act. It is the point at which all the mass of an object seems to be concentrated.

If a body is supported at its centre of mass, there is no turning effect in any direction and it balances.

For regular shapes, the centre of gravity lies at the intersection of the axes of symmetry:

• Rectangle and square: crossing of the diagonals.
• Equilateral triangle: crossing of the medians.

Finding the Centre of Mass of an Irregular Object

1. Hang the lamina from one point and allow it to swing freely.
2. Suspend a plumb line from the same point and mark the vertical line.
3. Repeat the process from a second point.
4. The centre of mass is the point where the two lines cross.

The plumb line must not touch the lamina so that it can rotate freely.