What is Mass?
The mass of an object tells us how heavy it is. It is a scalar measurement (i.e. it only has magnitude), and we can measure it by using scales.
Mass can also be described as the amount of 'matter' or 'stuff' in something. For example, a heavy ball has more stuff in it than a light ball. Similarly, if you've studied any chemistry, you know that a heavy atom has more particles in its nucleus than a light one.
Oxygen has more particles in its nucleus than hydrogen; consequently, it is a heavier atom.
What units do we use for mass?
Mass can be measured using lots of different units, including kilograms (kg), grams (g), ounces (oz) and pounds (lb).
An elephant has an average mass of around 5000 kg. The mass of a turtle is much smaller; a leather back turtle for example can weigh up to 900kg.
A paperclip, by contrast, only has a mass of about 1 gram.
What's the difference between mass and weight?
As we've already said above, mass is a scalar measurement, and it tells us how heavy something is. The mass of an object is constant, irrespective of where it is.
Weight on the other hand is a vector measurement and is a type of force. It is the measurement of the pull of gravity between an object and earth or other similarly large bodies. It is measured and reported using the unit Newton (N). The weight of an object will vary, depending on the gravitational pull of the environment it's in e.g. on earth or in space.