UNIT 5:

GRAVITATION...

Q. what is meant by the force of gravitation?

Ans. The force of attraction between any two objects of the universe is called “force of gravitation”.

Q. Do you attract the Earth or the Earth attracts you? Which one is attracting with a larger force? You or the Earth.

Ans. Earth attracts the person towards its center and person also attracts the earth with the same force.

Q. What is a field force?

Ans. The force of attraction of earth acting on an object with in gravitational field is called field force.

Q. Why earlier scientists could not guess about the gravitational force?

Ans. Gravitational force is of very small value and can be detected only by a very sensitive instrument that was not invented in old ages. That is why earlier scientists could not guess about the gravitational force.

Q. How can you say that gravitational force is a field force?

Ans. A body cannot experience a force of attraction of earth or of any other object if it is out of field of earth or of other object. So it shows that gravitational force is a field force.

Q. Explain, what is meant by gravitational field strength?

Ans. The gravitational force experienced by a unit mass in the gravitational field is called “gravitational field strength”. Its value changes with the change of altitude.

Q. Why law of gravitation is important to us?

Ans. The law of gravitation is used to calculate the mass of earth. It is also used to calculate the force of attraction on between two masses. So this law is important to us.

Q. State the law of gravitation.

Ans. According to this law,

“the force of attraction between two masses is directly proportional to product of these masses and inversely proportional to the square to the distance between the centers of the masses.”

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Q. How the mass of Earth can be determined?

Ans. The mass of the earth can be calculated by rearranging the following formula.

 

Here,

By putting the values of g, R and G, the mass of earth can easily be calculated.

Q. Can you determine the mass of our moon? If yes, then what you need to know?

Ans. Yes, the mass of the moon can be calculated by using the law of gravitation. The values of g, R and G for moon should be known.

Q. Why does the value of g vary from place to place?

Ans. The value of “g” varies with altitude. The value of “g” and altitude are of inverse proportion. So it varies place to place.

Q. Explain how the value of g varies with altitude?

Ans. The value of “g” has inverse relation with altitude. With increase of altitude the value of “g ” decreases. It can be calculated by the following formula,

Q. What are artificial satellites?

Ans. The objects sent into the space revolving around the earth are called artificial satellites. These are used for communication and research purposes.

Q. How Newton’s law of gravitation helps in understanding the motion of satellites?

Ans. The gravitational force of earth supplies the necessary centripetal force to the satellite which keeps the satellite the in circular orbit.

Q. On what factors the orbital speed of a satellite depends?

Ans. The orbital speed of satellite depends upon the altitude of from the center of earh. It is given by,

Q. why communication satellites are stationed at geostationary orbit?

Ans. The communication satellites complete their one rotation as the same rate as that of earth. So these are stationary w.r.t earth and called geostationary satellites.