ACCELERATION DUE TO GRAVITY

 

All bodies near the earth’s surface are attracted by earth towards its centre. This property is called gravity. Gravity is the force of attraction exerted by the earth on the bodies lying on or near its surface and the term is reserved for bodies on the earth’s surface only. For bodies on the surface of other planets or satellite, one uses the term gravitation.

If the body is free to move, earth’s gravity will produce an acceleration. This acceleration is called acceleration due to gravity and is denoted by g. Its magnitude is same for all bodies irrespective of their masses. Besides earths, all other heavenly bodies also possesses gravitation and hence acceleration due to it. The acceleration due to gravitation on the lunar surface is g/6 where as gravitational acceleration on the sun is 27g.

GRAVITATIONAL FIELD

The phenomenon of gravitation has been presented, so far, by using Newton’s law of universal gravitation. Accordingly, a body exerts gravitational force on other body at the distance. This viewpoint is to present the effect of gravitation through fields. Accordingly every point in space around the massive body (mass M) is thought to possess a value for the magnitude of force that would act on a unit mass at that point, and a direction of force. Then, any other masses m brought at that point will experience a force equal to the value of the force acting on a unit mass at that point multiplied by the mass m. We say that the massive body M, also called gravitating body, has created a gravitational field around itself. It interacts with any other mass through this gravitational field.

In this way, by gravitational field, we mean the region around a massive body where a force a gravitational can be experienced.

                          

                        EXCAPE VELOCITY

If we throw a body vertically upwards, it returns to the thrower. If it is thrown turns with a larger velocity, it attains a greater height but again returns back. If we keep increasing the velocity the body would rise too infinitely and may not return to the thrower. This velocity is called escape velocity. In other words, it will escape the gravitational pull of the earth (or planets) and go into outer space.