Q. 13.9( 42 Votes )

Answer the following:

A. You can shield a charge from electrical forces by putting it inside a hollow conductor.

Can you shield a body from the gravitational influence of nearby matter by putting it inside a hollow sphere or by some other means?

B. An astronaut inside a small space ship orbiting around the earth cannot detect gravity. If the space station orbiting around the earth has a large size, can he hope to detect gravity?

C. If you compare the gravitational force on the earth due to the sun to that due to the moon, you would find that the Sun’s pull is greater than the moon’s pull. (you can check this yourself using the data available in the succeeding exercises).

However, the tidal effect of the moon’s pull is greater than the tidal effect of sun. Why?

Answer :

(a). No

Charges are shielded from electrostatic forces by keeping them inside hollow conductor as no electric field penetrates the conductor and both gravitational forces and electric forces are field forces i.e. A body or charge experience force due to other body because of interaction between its own field and field due to other body or charge. We does not allow external field to interact with field of charge so it does not experience any force but there is no method to shield a body from gravity because gravity is independent of medium and there is no material found which shields gravitational field or does not allow it to pass through it so external gravitational field interacts with gravitational field of body and hence body experience force.


(b). Yes


If the spaceship is large enough then the astronaut will definitely detect the Earth’s gravity as Gravitational Force on spaceship is directly proportional to the mass of spaceship so as mass of bigger spaceship will be large and hence if will experience noticeable amount of force which can be detected, we know gravitational force on a body is given as



Where, F is gravitational force


G is universal gravitational Constant


m1 is mass of first body which in this case is earth


m2 is the mass of second body which is spaceship


and r is distance between earth and spaceship


so as mass of spaceship m2 increases the gravitational force experienced by it increases and hence can be detected i.e. Gravity can be detected


(c). As we know Gravitational force is inversely proportional to the square of the distance



Where FG is gravitational force and r is the distance



Where G is universal gravitational Constant


m1 is mass of first body which in this case is moon


m2 is the mass of second body which is Earth or moon


and r is distance between earth and spaceship


so as the distance increases Gravitational force between bodies decreases and sun is at a far more distance than moon but mass of earth is so much greater than moon that despite of moon being closer to earth force due to sun is greater


But in case of Tidal Pull it is observed that it is inversely proportional to cube of distance i.e.



Where FT is tidal force or Tidal pull and r is the distance


So here as the distance increases tidal pull decreases by a huge amount and hence since sun is very far away as compared to moon tidal effect of moon’s Pull is greater.


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