In what kind of gravitational field are Newton’s laws valid?
The newton’s law of universal gravitation states that a particle attracts every other particle in universe using a force that is directly proportional to product of their mass and inversely proportional to square of distance between them. F = G(m m /r ) 2 1 2 Universal gravitational constant G = 6.693 × 10 11cubic meters per kilogram second squared. Newton law of gravitation also similar to coulomb laws of electrical forces,which is used calculate magnitude of electrical force arises between two charged bodies.both are inverse square law but only difference is coulomb's law have product of two charges in place of product of masses. Here gravitational field is the influence that a massive extend into space around itself,producing a force on another massive body. The principle of equivalence implies that the known physical laws,valid in an inertial frame. All theory of relativity can be translated to the corresponding laws in a gravitational field. Example: the equation of motion of a particle in an arbitrary gravitational field follow from the law of inertia,which is valid in an inertial frame. Or Newton's laws are inappropriate in very strong gravitational field.in presence of very strong gravitational field the curvature of spacetime is large. If curvature is large the distance and time over the spacetime is approximately very small.then the distance and time over which it makes inertial frame becomes very small.because of that newton’s laws true only on very small scales.