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

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Solution

(a) No, gravitational force is a long range force and we cannot escape from it.

(b) Due to the small space ship, the force of attraction between the earth and the ship is too less, the astronaut cannot detect gravity. If the size of the space station is very large, the magnitude of the gravity will also become appreciable and hence he can hope to detect it.
(c) Generally, the gravitational force of attraction between two bodies is directly proportional to their masses and inversely proportional to the square of the distance between them. The gravitational force between the sun and the earth or between the moon and the earth varies inversely to the square of the distance. But due to the very large mass of the sun, the gravitational force on the earth due to the sun is about 7x10 times the force due to the moon on it.
The tidal effect varies inversely as the cube of the distance. Therefore, though the mass of the moon is quite small as compared to the mass of the sun, yet the tidal effect of moon's pull is very large (as compared to that due to the sun) due to small distance between moon and earth.

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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?

Compare the gravitational forces exerted by the Sun and the moon on the Earth. Which one exerts a greater force on the Earth? (Given: mass of the Sun, $M_{s} = 4 \times 10^{31} k g$ , mass of moon, $M_{m} = 6.3 \times 10^{22} k g$ , distance between the Sun and the Earth, $r_{s e} = 1.3 \times 10^{12} m$ and the distance between moon and the Earth, $r_{m e} = 4.5 \times 10^{8} m$ .

Q. Inspite of being much smaller than the Sun, why is the gravitational pull of the Moon greater than that of the Sun on the surface of the Earth?

Q. When the sun, moon and the earth line up in a straight line, the gravitational forces of the moon and the sun combine to pull the water on the earth much more than just the moon pulling the water alone. This kind of a tide is called a _____ tide.

Approximate the gravitational force exerted on the moon by the earth and the sun. A) during a solar eclipse and B) during a lunar eclipse. Given the mass of sun = 2 x 10³⁰ kg mass of earth 6 x 10²⁴ kg mass of the moon 7.4 x 10²² kg radius of earth's orbit around the sun 1.5 x 10¹¹m and radius of moon's orbit around the earth 3.8 x 10⁸ m.

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