An object is considered as a point object when the size of the object is very small compared to the distance it travels. That is, if an object’s size is negligible in comparison to the distance it covers, then we can consider it as a point object.
💡Why is this concept needed?
Consider a train. The approximate length of a train is about 400 meters. Even though a train does not look small to us, it can still be treated as a point object in certain conditions.
Since the train's length is negligible in comparison to the total distance travelled, we can consider the train as a point object in this case.
Now, consider a different scenario. Suppose the train crosses a pole on a railway track.
In which of the following examples of motion, can the body be considered approximately a point object: (a) a railway carriage moving without jerks between two stations. (b) a monkey sitting on top of a man cycling smoothly on a circular track. (c) a spinning cricket ball that turns sharply on hitting the ground. (d) a tumbling beaker that has slipped off the edge of a table.
To determine whether an object can be considered a point object, we compare its size to the distance it travels. If the object's size is very small compared to the distance it covers, we can approximate it as a point object. Let’s analyse each option one by one:
The size of the railway carriage is very small compared to the large distance it travels between two stations.
The size of the monkey is small compared to the distance it moves along the circular track.
The size of the cricket ball is comparable to the distance through which it turns sharply after bouncing.
The size of the beaker is comparable to the height of the table from which it falls.
Final Conclusion:
To approximate an object as a point object, its size should be negligible compared to the distance it travels.
