Notes- Gravitation class 9


Gravitation

 Gravitational force

Gravitation falling of apple
Every object present in the universe attract each other if any object is thrown upward it falls downwards towards the earth with gravitational force. Every object present on Earth is attracted by another object on earth or with the force that force is known as gravitational force.

The universal law of gravitation or Newton's law of gravitation.


Consider two objects of mass M and m are separated by a distance d. According to universal law of gravitation, the force between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
derivation of newton's Gravitation law
Importance of gravitation or the gravitational force
1. The gravitational force is responsible to bind the atmosphere.
importance of gravitation law

importance of gravitation law2. It is also responsible for the rainfall and the snowfall.
3. It is also responsible for the solar and lunar eclipse.
4. It is also responsible for falling off all the object towards the earth.
5. It is also responsible for generating Tides in the oceans.
6. It is also responsible for the revolution of the moon around the earth or revolution of the earth around the sun.
importance of gravitation law


Kepler's  Laws of planetary motion


gravitation kepler's first lawKepler had given three laws of planetary motion:-

1. Kepler's first law
According to Kepler's first law, All planet move around the sun in an elliptical Orbit and son is present at any one of the foci of this ellipse.



2. Kepler's second law
According to Kepler's second law of every planet sweeps equal area in equal interval of time.
gravitation-kepler's2nd law
 3.Kepler's third law
According to Kepler's third law, the square of the time period of a planet is directly proportional to the cube of the semi-major axis of that planet.

gravitation-kepler's 3rd law

How Newton guess Inverse Square Law
How Newton guess Inverse Square Law-gavitation

 Freefall

 It is defined as when an object come towards Earth under the action of gravity. This condition is called free fall.

Difference between mass and weight
Mass
Weight
1.     It is defined as the amount of the matter contained in a body.
2.     It is scalar quantity.
3.     It is constant quantity.
4.     Mass can never be zero.
5.     Unit of mass is kilogram or gram.
6.     Mass can be measured with beam balance.
1.     It is defined as the force with which an object that attracted towards the earth.
2.     It is a vector quantity.
3.     It is a variable quantity. It varies with Gravity.
4.     Weight can be zero at the centre of the earth.
5.     The unit of weight is Newton.
6.     Weight can be measured with spring balance.


Weight of an object on the moon is 1/6 weight of the object on the earth.
Let m→ mass of an object
Me →  mass of earth                 Mm→  mass of  moon
Re →  Radius of an earth                Rm→  Radius of the moon
We →  weight of an object on  earth
 Wm →  weight of an object on the moon
   
Weight of an object on the moon is 1/6 weight of the object on the earth-gravitation

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