WHAT IS MASS?
Mass is a measure of how much stuff is in an object or volume. All objects are made up of matter (stuff you can touch), mass is a measure of how much of this matter there is in an object.
This means that the object will have the same mass regardless of where it is in the universe, because it will be made of the same amount of matter wherever it is. For example, a ball will have a different weight on the Moon than it would on Earth, but in both cases it would have the same mass. See book on forces for more information about weight.
Mass can also be seen as the difficulty of accelerating an object. See book on acceleration. An object with a large mass will need a larger force to accelerate it than an object with a lower mass.
WHAT ARE THE UNITS OF MASS?
The standard unit for mass is the kilogram. One kilogram is equal to 1000 grams. Kilograms are used rather than grams as the standard unit because a gram is often too small to be useful in physics. In symbols a kilogram is kg
As a rough guide to how heavy a kilogram would feel on Earth, one litre of water or a pineapple is as heavy as an object with a mass of one kilogram.