ABSTRACT
This chapter considers the forces necessary to produce motion and the behaviour of bodies when forces are applied to them. The relationship between force and motion was formulated by Sir Isaac Newton. The acceleration vector always is in the same direction as the resultant force vector. A system of units in which the product of any two unit quantities is the unit of the resultant quantity is called a coherent system of units. Laws 1 and 2 apply only to motion relative to frames of reference which are either stationary or translating with constant velocity. Such frames are called inertial frames of reference and the acceleration measured in such a frame is always the absolute acceleration of the particle. The First Law is a special case of the Second Law; it represents the condition when the acceleration of the particle is zero.
