Motion (physics) Isaac Newton in his work "Philosophiæ Naturalis Principia Mathematica", first published on July 5, 1687. Newton's three laws are: Newton's three laws of motion were the first to accurately provide a mathematical model for understanding orbiting bodies in outer space. This explanation unified the motion of celestial bodies and motion of objects on earth. Classical mechanics was further enhanced by Albert Einstein's special relativity and general relativity. Special relativity is concerned with the motion of objects with a high velocity, approaching the speed of light; general relativity is employed to handle gravitational motion at a deeper level. Uniform Motion: When
Gravity knife Gravity knife A gravity knife is a knife with a blade contained in its handle, and which opens its blade by the force of inertia ("centrifugal" force) or gravity. As the gravity knife requires gravity or spinning motion to propel the blade out of the handle, it differs fundamentally from the switchblade, which opens its spring-propelled blade automatically upon the push of a button, switch, or fulcrum lever. The main purpose of this opening method is that it allows opening and closing to be done "one handed", in situations where the other hand is occupied. A major historical use has