ELASTICITY

      

INTRODUCTION

Every thing around us, with us and without us is matter. Everything in the materials world consists of matter. Atmosphere, air, water, trees, rocks, flesh, blood, bones, etc are the examples. Matter is every where in nature. It occupies the space and knowledge about it can be obtained using our organs of sense and instrument. It has mass and/or possesses energy. It is not spirit.

Matter is composed of particles called molecules and atoms. The size of the typical molecules is about 3×10ˉ10 m. Mechanical properties of matter are the topics our study in this and in the following two chapters.

The quantity of matter is a given substance is called it mass. Mass remain same even when its volume, shape or size change due to the external force, provided we don’t loose matter in the process. For example, substance like wool, cotton, rubber etc. can be compressed or stretched by Applying external force. But their masses do not change. Liquid and gases also flow, but their mass remains constant.

Constituents if matter

Matter is made up of a very large number of molecules. Each kind of matter has its own distinctive molecules. A molecule, in general, is composed of smaller particles called atoms. Atoms of elements were supposed to be invisible and were regarded as elementary particles with which all matter was assumed to be building up. In the beginning of the last century researches established the existence of more elementary particles, e.g. electrons, protons and neutrons. In the modern theory of matter an atom is made of a nucleus and electrons revolve around it. The nucleus is made of protons and neutrons.