Question

universal law of gravitation and its derivation for 9th class.

Answer 1

Universal law of gravitation state that every particle in the universe attract every other particle with the force which is directly proportional to the product of masses of the two particles and inversely proportional to the square of the distance between them and apps along the line and joining the two particles.
then according to the gravitational law
I) F is directly proportional to the m1m2. and
2) f is directly proportional to 1/d^2.
combining this two laws we get
F is directly proportional to m1m2/d^2.
F=G m1m2/d^2
G is constant of proportionality.
Hope this will help u
:-)

Answer 2

ANSWER:
Universal Law of Gravitation

1.Universal Law of gravitation was formulated by Sit Issac Newton.

2.It states that:
Every body in universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of distance between them. The force acts along the line joining the two bodies.

3.Derivation:
==>Now according to the universal law of gravitation as stated earlier , the force F is proportional to the product of masses of objects P and Q that is
==>F∝M×m (1)
and the force is inversely proportional to the square of distance between these two objects that is
F∝1/r^2 (2)
Combining both equations (1) and (2) we get
F∝Mm/r^2 (3)
or
F=GMm/r^2 (4)
==>Here G is the constant known as Universal Gravitational constant.
SI unit of gravitational constant G is Nm^2Kg^−2.

4.Value of G was first found by Henry Cavendish (1731-1810) and it is
G=6.673×10−11 Nm^2Kg^−2.