Question

State two applications of universal law of gravitation.

Answer 1

Hint: According to the universal law of gravitation, any two bodies in the universe attract each other by a force called gravitational force. This statement explains a lot of things such as the motion of the planets around the sun and objects falling back towards earth when thrown up.

Complete answer:
First, let's understand the universal law of gravitation. Then we can understand the applications of the law much better.
According to the universal law of gravitation, any two bodies in the universe attract each other by a force called gravitational force. Suppose there are two bodies A and B. Body A will exert a force on body B, directed towards itself. And body B will exert an equal force on A, directed towards itself. Note that both the forces are equal magnitude but opposite in direction.
The gravitational force between two bodies is directly proportional to the product of the masses of the two bodies and inversely proportional the distance between the centre of masses of the bodies.
Therefore, the gravitational force between two bodies of mass ${{M}_{1}}$ and ${{M}_{2}}$, their centre of masses being separated by a distance r is given as $F=G\dfrac{{{M}_{1}}{{M}_{2}}}{{{r}^{2}}}$.
Here, G is a proportionality constant.
Now we can discuss the applications of the law.
(i) The law of gravity gives us the reason why the planets in our solar system revolve around the sun.
The planets and other smaller celestial bodies revolve around the sun in elliptical orbits under the influence of the gravitational force of attraction exerted by the sun.
(ii) The gravitational law explains why a ball falls down when it is thrown upwards. This is because the earth exerts a force of attraction in the ball and therefore the ball accelerates downwards.
Similarly, we are able to be on the surface of earth and not flying in the air.

Note: To make an object fly in the air, one has to do work against gravity. In other words, one has to apply a force greater than the gravitational force that the earth exerts on the object and the direction of the applied force should be opposite to the direction of the gravitational force.
This is how a rocket or a bird flies in the air.