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| Concept of a Point Object |
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| A real object can rotate as it moves. |
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| For example, a cricket ball may be spinning while it is moving, as a whole, in a trajectory. Also, a body may vibrate as it moves, for example, a falling water droplet. These complications can be avoided by considering the motion of a very small body called a particle or a point object. Mathematically, a particle is treated as a point, an object without extension, so that rotational and vibrational motions are not involved. |
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| Actually, there is no such thing in nature as an object without extension. The concept of a particle or a point object is very useful because real objects often behave to a great extent, like particles. A body need not be 'small' in the usual sense of the word, in order to be treated as a particle. For example, if we consider the distance from the Earth to the sun, with respect to the distance between them, both the Earth and the sun can be treated as particles or point objects. We can find out a great deal about the motion of the sun, planets and other celestial bodies, without appreciable error, by treating these bodies as particles. Moreover, any object can be treated as a point object if it covers distances which are much greater in comparison to its size. A cricket ball moving in a field and a train covering hundreds of kilometres, are some examples. |
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