This unit deals with how the physical quantities such as displacement, velocity, acceleration and time are related each other quantitatively. Formulas are employed in all uniform and accelerated motions. However, graphical methods are applied for uniform motion only. It was believed by Philosophers of antiquity that an unbalanced force requires to set an object in accelerated or uniform motion. Later Sir Isaac Newton clarified which types of motions require unbalanced force and which ones can be done without any intervention of net force. The other important observation of Newton was that forces always exist in pairs. Newton described all these phenomena in his three laws which are the concern of this unit. According to Newton’s laws, in the absence of unbalanced force an object can move with constant velocity but it requires net force to accelerate. So why do other objects accelerate towards earth’s center when they are released freely? This question is again answered by another universal law known as Newton’s law of universal gravitation, which was again an outstanding finding of Sir Isaac Newton. This law is treated around the end of the unit.