State the universal law of gravitation and derive its expression.
The universal law of gravitation states that the force of attraction between two masses m1 and m2 separated by a distance r is directly proportional to the product of the masses and inversely proportional to the square of the distance between the masses.
F α m1m2
F α 1/r2
Or, F = Gm1m2/r2
Where, G is a constant called the universal gravitational constant and is equal to 6.67 × 10-11 Nm2/kg2