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Mass is the quantity of matter contained in a body.
If you push a book, it moves faster than if you push a car with the same force. This is because the car has more mass than the book. If you had two identical boxes, one containing iron and the other containing cotton we could identify them by pushing the boxes. We can say that the car and iron box are more reluctant to move than the book and the cotton box. We call this reluctance to move "inertia". Larger the mass of an object, larger is its inertia. Hence mass of a body is a measure of its inertia.
Moving objects have inertia too. A moving object needs force to make it stop. A moving car has more inertia than a moving book. It needs more force to make it stop.
Mass can be measured by finding out the force needed to change the way the object moves. The greater the force needed, greater the mass of the object.
Mass can also be determined by comparing the weight of it with the weight of a known mass, a standard mass. For this we can use a lever balance on common balance.
This balance consists of a beam and two scale pans (shown in figure below), the beam being balanced at its mid point on a knife-edge. The scale pans also hang on knife edges and rest on the base board. When the balance is not in use the beam rests on the beam support.
A Laboratory Balance
