You’ll start by quickly looking at why this section is called mass rather than weight. Weight is the word that most people use in everyday language to describe how much ‘stuff’ is in an object. However, in science weight does not measure this quantity. In fact, the correct term for the amount of ‘stuff’ in an object is ‘mass’. The two quantities are related, but have different meanings.
Weight, on the other hand, is the force due to gravity on an object (or a mass). As mass is a measure of the amount of ‘stuff’ in an object, this doesn’t change unless you physically alter that object. However, the same object would not have the same weight on the moon as it does on the earth. Its weight would reduce because the moon has a lower gravity than the earth. They are also measured in different units! So, to be strictly accurate, the course uses the correct term: ‘mass’.
Now it’s time to look at the SI units for mass.