State Newton's Universal Law of Gravitation. Explain how the value of the Gravitational constant can be determined by Cavendish method.

State Newton's Universal Law of Gravitation. Explain how the value of

1.	State Newton's Universal Law of Gravitation. Explain how the value of the Gravitational constant can be determined by Cavendish method.
Answer» Solution :Newton's law of GRAVITATION : Every BODY in the universe attracts every other body with a force which is directly proprotinal to the product of their masses and inversely proportional to the square of the distance between them. `F prop m_1M-2" and " F prop (1)/(d^2)" or "F prop (m_1m_2)/(d^2)` or `F=(Gm_1m_2)/(d^2)` This is always a force of attraction and acts along the line joining the two bodies. Canvendish experiment to find gravitationl constant 'G' : Cavedish experiment consists of a long METALIC rod AB to which two small lead spheres of mass 'm' are attached. This rod is suspended from a rigid support with the help of a thin WIRE. Two heavy spheres of mass M are brought near tothese small spheres in opposite direction. Then gravitational force will act between the spheres. Force between the spheres, `F=(GMm)/(d^2)` Two equal and opposite forces acting at the ends of the rod AB will develop force couple and the rod will ROTATE through an angle `'theta'`. Torque on the rod `FxxL=(GMm)/(d^2)L to (1)` Restoring force couple= `tautheta to(2)` Where `tau` =Restoring couple per unit twist `:. tau theta=(GMm)/(d^2)L" or " G=(tautheta d^2)/(MmL)` By measuring `theta` we can calculate 'G' value when other parameters are known. Practical value of G is `6.67xx10^(-11) Nm^2`/`kg^2`.