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.
Dynamics (mechanics) - Newton's laws. 1  Newton described force as the ability to cause a mass to accelerate. 2  First law: If there is no net force on an object, then its velocity is constant. 3  Second law: The rate of change of linear momentum P of an object is equal to the net force Fnet, i.e., dP/dt = Fnet.