To make a student understand what Field in Physics means in simple terms, and also to make the student visualize that Field is a Vector which has both a magnitude and direction; can be challenging. The only way to me is by giving analogy and then leave it to the student to overlay that experience he/she undergoes to absorb then internalize the concept of Field.
So, let us again return to a “Thought Experiment”. Say, a father brings a bunch of Roses for his wife and keeps it as a surprise in their bedroom. No sooner when the student (their child) returns from the school, he/she finds the fragrance of Roses is spread in the entire house. However, when the child was in the school or even outside the house on the road, the same fragrance could not be experienced. This attracts the child and he/she moves towards the direction in which the strongest smell of Roses is, and finally reaching the bedside table of his parent’s bedroom where Roses had been kept. This fragrance had an intensity and a direction by which the child got pulled towards the location where Roses were kept.
So, Field too behaves in this very manner. It has an influence spread out in space and affects the bodies which interact with the Field. In this case, the child interacts with the effect of the fragrance and under it finally reaches the point where fragrance is most intense.
Now we can understand the Gravitational field from this experiment as stated in the Law of Gravitation. In other words, the reason why things around us fall to the surface of the earth is that the Gravitational Field acting on them.
It then raises a very interesting but related question vis a vis the Gravitational field. Is there like the fragrance of Roses a location in space, where the Gravitational field of Earth does not affect another physical body? The answer is YES! There is an imaginary but definite surface surrounding our Earth in space where the Gravitational force of attraction ends and when a physical body crosses that surface, it will not return to earth as it is out of the Gravitational force of attraction. And it holds good for other planets too in space as the primary requirement in the Law of Gravitation is the existence of the mass of a physical body.
This can also be found true mathematically by recalling that the Gravitational Force (F) of attraction is Inversely proportional to the Square of the Distance (r) between the two bodies having a mass (m). Hence, by simple calculation one can determine at what distance from the earth the force of earth’s gravitation will become zero, meaning will be no more effective, in this case say when a rocket is sent in space.
Evidence, all rockets sent to Moon cross that imaginary surface after which the effect of Earth’s gravity remains no more. In Physics we call it “escape velocity” by which a body must sent in space to get out of Earth’s gravitational pull. It can be easily calculated.
April 06, 2021