Consult your doctor if: 1  Your headache symptoms occur more than 15 days a month or require frequent over-the-counter pain medicine. 2  You have a severe headache, and over-the-counter pain medicine doesn't help. 3  You miss school or work because of frequent headaches or the headaches interfere with your daily life. 4  Definition. Causes.
Newton's law of gravitation. (nt'nz) The principle that expresses the force of gravitational attraction between two bodies as a function of their mass and their distance.
Gravity, or gravitation, is one of the fundamental forces of the universe. In everyday use, it describes the force which causes objects to fall onto the ground. Newton's laws discusses how gravity keeps the Solar System together and Einstein's theory of general relativity is about the role of gravity in the universe.