Matric Part-1 Grade 9 Physic Notes Chapter 5 Gravitation Important board questions, Short questions, Long questions, Numerical Problems, and Mcqs download the PDF or view it online for FREE.

## Gravitation Physics Notes Class 9th

Table of Contents

**Q.1** **state and explain Newton’s law of gravitation?**

**Ans. Newton’s universal gravitation:- **

__this law states that in this universe Avery two bodies attract each other with a force which is directly proportional to the product of their masses and inversely proportional__to the square of the distance b/w them.

** Explanation**:- consider two bodies a and b as shown in the figure let their masses are m

_{1}and m

_{2}respectively and the distance b/w they is “r” then according to Newton’s law of gravitation the force of attraction :f: is given as:-

F m_{1}m_{2 ……………………………} (i)

F 1/r_{2 ……………..(ii)}

_{ }Combining eq (i) and eq (ii) we get.

F m_{1}m_{2 1/}r_{2}

F m_{1}m_{2 1/}r_{2…………….}(iii)

Eq (iii) is the mathematical form of Newton’s law of gravitation. Where “G” is gravitational constant and its value is equal to 6.673 x 10^{-11=} N.m^{2} /kg^{2}

### using the law of universal gravitation find the mass of the earth?

**Ans. **we can find the mass of earth “Me” by using universal gravitation by following the method suppose we have a body of mass “m” laying on the surface m of the earth as shown in the figure.

Let “m” is the mass of the body “Me” by the mass of the earth “Re” is the radius of the earth which is the distance b/w the centres of the body and the earth. Now according to the law of universal gravitation, the force b/w earth and object is given by:-