Analysis: Centres of gravity of composite bodies

If you know the location of the centre of gravity of each component of an object you can find the overall centre of gravity of the whole thing.

You do it by taking moments.

We’ll use the method on composite objects where the components are rectangles, circles or triangles. We know the location of the centre of gravity for all of these.

If you know calculus you can apply this method to a wide range of geometric shapes. For example you can prove the standard result for a triangle. But that’s for another time.

For now we’ll stick with simple shapes and show you how to keep track of your working by using a table. A table suits a spreadsheet perfectly.

Talking points

• What do you think are the benefits of a table when using the method of composite bodies?
• Under what the circumstances, if any, would you not use a table?