If you take anything away from physics, let it be this: weight is not the same thing as mass. Confused? In short, mass is a measure of how much stuff is in an object, while weight is the gravitational force that acts on that stuff.

So basically, weight is the result of gravity. The conversion factor, g, (10N/kg on the earth) has units that divide out the kilograms and multiply by N. Lastly, while weight is measured in newtons, mass is measured in kilograms.

Right, now we’ve got that sorted, let’s get cracking! Because it’s always good to use examples in science, feel free to whip this one out come exam time; if you ever need to work out what the centre of mass for an object hung from a thread will be, it is below the suspension point.

This is because an object’s mass is spread across its entire volume. So its weight acts on all of it. However, for simplicity, there is one point where the weight effectively acts; this is the centre of gravity.

If an object hangs from a thread it will always come to rest with its centre of mass below the suspension point. If you consider the point where the thread attaches as a pivot you can see why. If the centre of gravity is to the left, there is a turning force to swing it to the right, and vice versa.