Mass is (among other properties) an inertial property; that is, the tendency of an object to remain at constant velocity unless acted upon by an outside force. Under Sir Isaac Newton's 337-year-old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram accelerates, a, at one meter per second per second (about one-tenth the acceleration due to Earth's gravity) when acted upon by a force, F, of one newton.