University of Edinburgh

BSL Physics Glossary - force - example

Forces – how to measure weight or mass of an object

We can use this Newton balance to measure forces or weights. This is the sign for the Newton balance, linked to the hook on it. The unit used for measuring forces is the Newton.

This has a mass of 5kg. It's heavy! But what is its weight?

Remember the formula for weight: Weight = mass x gravitational field strength

Earth's gravitational field strength (gfs) is 10 N/kg.

So 5 x 1 = what? 50 Newtons. Let's have a look.

It's 50 Newtons. That's its weight.

Now let's try to find the weight of this metal ball. What do you think it will be?

It's 20 Newtons. So what must its mass be?

Remember, weight = mass x gfs

So 20 = mass x 10

Rearrange the formula to give: 20/10 = mass

Do you know what the mass is? Yes, it's 2 kg. It says that on the bottom.
So that's how we can calculate the weight and mass of an object.