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| Mass |
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| Mass is the quantity of matter in the body. Mass is 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. |
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| 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". The larger the mass of an object, the larger its inertia. Hence mass of a body is a measure of its inertia. |
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| 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. |
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| Measurement of Mass |
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| Mass can 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. |
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| Common Balance |
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| 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. |
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| A Laboratory Balance |
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| How to use a balance? |
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 Use the levelling screws, attached beneath the base board to make sure that the beam is horizontal. It can be verified with the help of the plumb- line provided shown in the diagram. |
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Use the arrestment knob to raise the beam and the adjusting screw at the two ends of the beam, to bring the pointer to the middle or zero mark on the scale. |
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Lower the beam using the arrestment knob again. |
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Place the body to be weighed on the left scale pan and put weights on the right hand scale pan to balance the beam (when pointer is at zero). |
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