Gravitation chapter detailed notes for class 9 by satyam raj

                    GRAVITATION 

● Every object in the universe attracts every other        object with a force called "GRAVITATIONAL FORCE".

■ Universal law of gravitation 

> According to Newtons universal law of gravitation,  force acting on two bodies of masses m1 and m2 kept at a distance of 'r' is __

(i) directly proportional to the product of their masses

                F ∝ m1×m2    ------------------ (i)

(ii) and inversely proportional to the square of distance between them. 

               F ∝ 1/r²          ----------------------- (ii)

On combining equation (i)and(ii) we get ------

          F ∝ m1×m 2 / r²

> F = (Gm1m2)÷r²

Where G is a constant called universal gravitational constant and it does not depend on 

●mass of bodies 

●distance between them or 

●the medium in which bodies are kept.

● The SI unit of universal gravitational constant G is Nm²/kg² .

~ F =Gm1m2/r²

Let m1 = 1kg, m2 = 1kg ,  r = 1m

Then we get [ F = G ].

>> Universal gravitational constant G is numerically equal to the force of gravitation b/w two bodies each of unit mass kept at unit distance from each other.

>> Application of Newtons law of gravitation or Universal gravitational constant "G". <<

Newtons law of gravitation help to __

1. Explain the motion of planets moving around the sun.
2. Explain the motion of satellites 🛰  around the planets.
3. Explain the formation of Tides in the sea.
4. Measure the masses of sun , earth and moon accurately.
5. Discover new planets and stars.    

>>KEPLERS LAW OF PLANETARY MOTION <<

• In 16th century keplers gave three laws regarding motion of planets around the 🌞 SUN.

[1] ........FIRST LAW.........

• Every planets moves around the sun in and elliptical orbit with the sun present at one of the two focus.

[2]..........SECOND LAW............

• Keplers 2nd law states that the line joining from planet to the sun sweeps over equal areas in equal interval of time.

      •~   [ A1 = A2]

NOTE:

●This law also given the following information __

•when the planet is far from the sun it moves with slow speed.

•when the planet is near to the sun it moves with greater speed 🌎. 

>>[Nearest position of planet from the sun called PERINELION.]

>>[ Farther position of planet from the sun 🌞  called APHELION].

[3].........THIRD LOW..........

The ratio of cube of mean distance from the planet to the sun and the square of time period which a planet takes to revolve around the sun is always CONSTANT.

That is _______

>     (Mean distance)³ ∝ ( Time period )²

>      r³ ∝ t²

>      r³ = constant × T²

<      r³/t² = constant.

Thanks for reading my notes 📝 📋 

                           

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Made by satyam raj.