GRAVITATION.

GRAVITATION

1. State heliocentric and geocentric theory.

- Heliocentric theory states that “ the sun is at the center of the universe and all other planets and satellites revolve around the sun in their own axis” and geocentric theory states that “the earth is at the centre of the universe and all the heavenly bodies like the sun, the moon etc. revolve around the earth”.

2. Define gravitation.

- The force of attraction between any two objects of the universe due to their masses is called gravitation.

3. When the apple falls, does it attract the earth?

- Yes when the apple falls it attracts the earth. However, due to less mass the apple cannot create the noticeable acceleration like earth does to the apple. Hence, we see apple moving towards earth but not vice versa.

4. Define Newton’s universal law of gravitation.

- It states that “the gravitational force acting on any objects in the universe is directly proportional to their masses and inversely proportional to the square of the distance between their centers.”

4. Define G and illustrate it’s properties.

- Newtons universal gravitational constant (G) is defined as the gravitational force between any two  objects having unit masses and separated by unit distance. Its properties are:

   1. The value of G is not affected by  temperature, pressure and time.

   2. It is independent of direction of gravitational force.

   3. It is independent to the nature of the masses.

Therefore, it is constant.

5. What are the consequences of gravitational force.

- The consequences of the gravitational force are:

   1. Earth holds the atmosphere.

   2. Due to mutual gravitational forces between the sun, the moon and the earth, the tides are formed on the oceans.       

   3. It is responsible for rainfall, snowfall etc.

   4. The object thrown upward falls down.

6. Define gravity or weight with it's S.I unit.
- The force of attraction exerted by the earth on a body is called gravity or weight. It's S.I unit is Newton. Mathematically,     W=m x g

7. Define Mass.
- The total amount of matter contained in a body is called mass. It's S.I unit is kg.

8. Define acceleration due to gravity with it's unit. Derive an expression for it.
- The acceleration produced in a freely falling body due to earths gravity is called acceleration due to gravity. Let F be the gravitational force, M be the mass of the earth and R be it's radius.

9. Write the factors on which acceleration due to gravity depends.

- Acceleration due to gravity depends upon following factors:

1. Directly proportional to the mass of the earth.

2. Inversely proportional to the square of the radius of the earth.

NOTE- It is independent to the mass of the object lying on the earth's surface.

10. What are the effects of gravity?
-  The effects of gravity are:
1. River flows due to gravity.
2. Acceleration is produced in falling object.
3. The earth is covered by atmosphere.
4. Objects thrown upward return to the earth's surface.

11.  Why is it difficult to lift larger stone?
- Since,  weight= mass x acceleration due to gravity, we know larger stone has more mass which means it has more weight. Hence, it is difficult to lift larger stone.

12.  Explain Guinea and Feather experiment.
- A Guinea and feather are placed in a long and wide glass tube, when they are at bottom the tube is inverted. In this case the coin falls faster than feather but when a vacuum is created in a glass tube and is inverted, the coin and feather falls simultaneously.
Conclusion- The acceleration due to gravity is independent of masses in absence of air resistance.                           
                                                   

13. What is the value of g at poles and equator of the earth?

- The value of g at poles and equator are 9.83 m/s/s and 9.78 m/s/s respectively. (m/s/s=meter per second square)

14.  The value of g is more at pole than in equator, why?

- We know, g=GM/R^2

As earth is bulged out at the equator and flat at poles, radius of equator is greater than radius of pole and from above formula it is clear that more the value of radius less will be the value of g. Hence, g is more at pole than in equator.

15. Define gravitational field and gravitational field intensity.

- Gravitational field is defined as the area around the heavenly body up to which its gravitational force can be felt.

- Gravitational field intensity is defined as the force experienced by a unit mass kept at any point in gravitational field. It's S.I unit is N/Kg.

16. Define free fall and weightlessness.

- If an object falls freely only under the effect of gravity neglecting air resistance, the body is said to be in a free fall. For example, object falling on the surface of the moon.

- Weightlessness is defined as the condition in which effective weight of a body becomes zero.For example, When a person falls freely in a lift.

17. What are the condition for weightlessness.

-  The conditions for weightlessness are:

a. In free fall.

b. At the center of the earth.

c. At null point outside Gravitational field.

d. In satellite orbiting round the heavenly body.

18.  The weight of the body is more in the terai than in the Himalayan region, why?

-  We know, weight= mass x g  

and,                                                    

Clearly the g is inversely proportional to the square of the  distance from the center of the earth, as terai has less distance from the center of the earth , g is more at terai and hence weight of the body is more in the terai than in Himalayan region.

19. The value of 'g' is zero at the center of the earth, why?

- We know, acceleration due to gravity at the center of the earth is given by g=(1-d/R).g and the value of d=R at the center of the earth so the value of g becomes zero.

20.  What is the difference between the falling of parachute on the earth and the moon?

- In earth, due to the presence of air resistance the parachute falls slowly with constant velocity called  terminal velocity (WHICH MEANS g=0 m/s/s) but due to absence of air resistance on the moon the falling of parachute is a free fall.

21. Can masslessness be called weightlessness, why?

- No, because mass is constant quantity where as weight varies from place to place and the body experience weightlessness only due to zero reactional force which may be due to zero gravity or free fall.

22. Moon doesn't have atmosphere, why?

- Due to it's insufficient gravity which produces acceleration of only 1.67 m/s/s, the moon cannot retain the atmosphere and hence, it is atmosphere less.