# Introduction

The study of kinematics involves, description of motion of point objects in one, two and three dimensions. The motion of point objects is explained and equations of their motion are derived using their position co- ordinates and other relevant parameters.

Newton's Laws of motion are applicable to the motion of both finite or extended objects. But are not applicable to atoms and molecules. Laws of quantum mechanics are applicable in describing their motion.

The key concept involved in the study of motion of extended objects is the concept of centre of mass of a system of point objects which constitute the extended object.

In earlier chapters, we worked with ideal point particles, even though we applied the results to objects of finite size. As every body consists of many parts, is it correct to treat the body as a point object?

Only some parts of a body feel the external forces, so what are the forces, which the different parts of a body exert on each other?

When concepts like position, velocity, and acceleration are used, these could be different for different parts of the same body.