Mass vs. Weight
Mass is the amount of matter in an object. We're talking about how many atoms there are in the object, and what type of atoms they are, i.e. how many protons and neutrons are there in each atom.
A large mass is more difficult to accelerate than a smaller mass. We say that the large mass has a bigger 'inertia'.
A typical example is to compare how difficult it is to get a locomotive moving (an object with a large mass) compared to a toy car (an object with a relatively small mass). It is much more difficult to accelerate the locomotive and so we say the locomotive has a much greater mass.
So what is meant by the WEIGHT of an object? This is often confused in every day language because people ask, "How much does the object weight?", when what they are really asking is, "How much mass does it have?"
Mass is the amount of matter and is measured in units of kilograms (kg).
Weight is a force and is measured in units of newtons (N). This force is the pull of gravity on a mass. A large mass has a large gravitational field so that it attracts other masses with more force (or weight).
In reality, to create a weight force that is noticeable, we need something with a HUGE mass, for example, the Earth.
How can different weights and masses be compared? The simplest way of comparing masses is to measure their weight (the force that Earth pulls down on them) by using a top pan (spring) balance.
You could also use a pair of weighing scales to compare masses. The larger mass will make the scales tip on that side, or you could balance the scales if the masses are the same.
GCSE Physics keywords: Mass, Kilograms, Matter, Weight, Newtons, Force