Since a central force F acts only along the radius, only the radial component of the acceleration is nonzero. By Newton's second law of motion, the magnitude of F equals the mass m of the particle times the magnitude of its radial acceleration F ( r ) = m r ¨ ¨ − − m r ω ω 2 = m d 2 r d t 2 − − m h 2 r 3