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Centre of Mass

Centre of Mass

Centre of Mass

The centre of mass is an imaginary point of any object that weight acts through. You will discover how this can be determined as well as the effect of changing its position.

In which direction does weight act?

An object always acts straight towards the centre of the Earth. So which part of an object does the weight act from?

What is the easiest and most accurate method of finding the middle point of a regular shape such as a square?

The centre of mass is the point in an object where the weight will act from as weight=mass×gravityweight=mass\times gravity. In a regular object this will be where the lines of symmetry meet to show us the middle point.

Which one of the following options do you think we could use to find the centre of mass of an object with an irregular shape?


In order to calculate the centre of mass of an object with an irregular shape you need to use some string and a clamp.

You hang the object and place a hole in it before hanging the string from the hole. This creates the plumb line. You then repeat this from a different hole in the object. Where the two lines cross is the centre of mass.

What would happen if the centre of mass moves in an object (such as a stool being tipped onto two legs)?


The image shows what happens if you tip an object and change the centre of mass.

Diagram 3 shows that if the centre of mass causes the force to act outside the base of the object, the object will tip over!