Posted in Physics Revision

Centre of Mass

P 3 3.3

Mechanics has a reputation for being difficult and making students panic, but it doesn’t need to be. We’ll start with the basics and work our way into the tricky stuff.

Definition: The point at which an object’s mass may be thought to be concentrated.

Image result for centre of mass of regular shapes

It’s very easy to find in regular objects, as you can see above.

In irregularly shaped objects, it’s a little more complicated than that, and some examiners enjoy asking you the method for finding it. It’s called the plumb-line experiment.


1) Pin a piece of string through a point at the edge of an irregular shape, hanging a pendulum at the other end.

2) Draw a line where the string hangs.

3) Repeat several times on different points.

4) Where the lines cross is the object’s centre of mass.


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