2 CHAPTER 1. PROPERTIES OF MATTER
recreation, food production, medicine & health care, etc. History of civilisation can be
termed as the history of howhomo sapienslearned to use various materials and gained
ability to alter material properties to suit various requirements. This can be seen from
the manner in which early epochs of human civilisation are named stone age, bronze age,
and iron age on the basis of the prominent materials used for tool making during the
respective periods.
When subjected to external influences (or stimuli), materials give rise to specific re-
sponses. For example, when subjected to a su ciently large external force, a material
will undergo changes in shape and size, when heated a material may undergo a struc-
ture change or change of state, when placed in contact with certain other substances a
material can undergo chemical reaction, etc.Property is a material trait in terms of the
kind and magnitude of response to a specific imposed stimulus. Generally, definitions of
properties are made independent of material shape and size. During engineering applica-
tions, materials undergo di erent kinds of external stimuli and therefore it is important to
have in-depth knowledge of material response, i.e., material properties, for designing and
devising better engineering systems. All important properties of solid materials may be
grouped into six di erent categories: mechanical, electrical, thermal, magnetic, optical,
and deteriorative. For each, there is a characteristic type of stimulus capable of provoking
di erent responses. Mechanical properties relate material deformation to an applied load
or force; examples include strength, hardness, ductility, and sti ness. Many materials,
when in service, are subjected to forces or loads; for instance, the aluminium alloy from
which an airplane wing is constructed or the steel in an automobile axle. In such situations
it is necessary to know the characteristics of the material so that any deformation that
may occur during service will not be excessive and fracture will not occur. It is incumbent
Figure 1.1: The Akashi Kaikyo suspension bridge in Japan has the world’s longest
mainspan.Source: Wikipedia