Above shown items are results of combination of different solids. Gems which are mainly used for jewelry purposes, silicon chip used in computers, coins made of gold, porcelain pots are the examples of solids which are encountered in daily life.
Diamond and its structure
Ever since humans started to take an interest in the world around them, they have studied the appearance and feel of objects and materials they encountered. Gradually they experimented with materials to discover how they could be used.
In this age of high technology, nobody can undermine the importance of understanding materials. New man–made materials, alloys have found immense applications in our daily lives. Who can forget the importance of steel, plastics, nylons, superconducting alloys, semiconductors and other new materials?
The properties of solids depend on electronic configurations of its constituent elements. It is the electrons that take part in chemical reactions and therefore their interactions are the main factors that determine the outcome of the behavior of a solid.
We can have a good feel for a solid if we know about their few basic properties:
- Density of a solid
- Pressure exerted by a solid
- Elastic properties of a solid
Sodium chloride crystal
Regular arrangement of Na+ and Cl- ions result in a crystal with definite geometry. As a result NaCl is crystalline in nature
As the density and volume are in inverse relation with each other, when the volume is decreased, the density increases. Here when the volume of bread is decreased then automatically density increases.
Density of solid:
It's a measure of the compactness of matter, of how much mass occupies a given space; it is the amount of mass per unit volume.
Density is usually expressed with metric units, generally kilograms per cubic meter, kilograms per liter, or grams per cubic centimeter.
Relative density can be easily understood by observing the above diagram. A wood block floats on water as its density is less than that of water. While piece of iron sinks to bottom of container containing water as the density of iron is greater than that of water.
Hitting the nail on its head with hammer is the everyday example of pressure that we encounter in our daily life. We hit the nail on its head perpendicularly so that maximum force acts on head which is then magnified at the sharp end of nail. The explanation for this phenomenon is that force would be same on the nail, but pressure varies at two ends due to variations in area at both ends. Pointed end exerts more pressure as its area is very much smaller than area at head of nail. Thus pointed end forces the nail into wall with magnified amounts of pressure.
Effect of temperature on density:
Most of the substances expand on heating and contract on cooling, but the mass remains unchanged. Therefore, the density of such substances decreases with the increase in temperature and increases with the decrease in temperature.
The relative density of a substance is the ratio of the weight of any volume of the substance to the weight of an equal volume of water.
Pressure exerted by a solid:
Keep a book on the palm of your hand. As we know, the weight of an object is the force with which it is pulled vertically towards the earth. Thus, a force equal to the weight of the book acts downwards on the palm, in a direction perpendicular to the palm. An equal and opposite force is exerted on the book by the palm, which keeps the book stationary. In the above example, a force acts perpendicular to the surface, and this force is called thrust. Its SI unit is Newton (N).
The effect of the thrust depends on:
- The magnitude of the force
- The area on which the force is acting.
Pressure is defined as the thrust per unit area.
The unit of pressure is Pascal (Pa), which is equal to a force of 1 N over an area of 1 sq. m.
Stretching of a spring on applying force.
Springs possess a characteristic property of compression and elongation. When the weight suspended to the spring is increased, the spring results in elongation up to certain limit of weight and when the weight suspended is removed it regains its original shape.
Elastic properties:
Solids have definite shapes in addition to sizes and hence they can have deformations of shapes as well as of sizes. If a deformed body regains its shape or size when the deforming forces are removed, we say the body is elastic. Thus a spring, a rubber band or a gas filled in a balloon are elastic, to some extent.
We can visualize an elastic solid as an array of particles joined together by springs. When deforming forces are applied, the springs get elongated or compressed. In trying to regain their original shape, they exert restoring forces on the particles. When the deforming forces are removed, the restoring forces bring the solid back to its original shape and size. The property possessed by a material body, due to which it regains its original dimensions, as soon as any deforming forces acting on it are removed, is called elasticity.
Stress & strain:
- Stress is the internal restoring force per unit area, generated within a body when it is deformed under an external force.
- Stress = F/A
- The unit of stress is Pascal or N/m2.
- The ratio of change in length to original length is called tensile strain ( l/L ).
- The ratio of stress to strain is called modulus of elasticity.
- Modulus of elasticity is measured by various parameters such as
Hooke's law:
A British physicist Robert Hooke noted the relationship between external applied force and elasticity in the mid–seventeenth century. The relationship is known as the Hooke's law. The amount of stretch or compression (change in length), dx, is directly proportional to the applied force F.
In shorthand notation, F ∼ dx
The principle that when a body is deformed, within its elastic limit, the strain produced is directly proportional to the stress, and this is known as the Hooke's law.
Elastic fatigue:
The elastic fatigue is defined as the loss of strength of the material by subjecting it to repeated or alternating strain. To avoid elastic fatigue, some precautions are always taken.
Gaps between the bridges are left due to the fact that solids expand on heating. Gaps allow the materials of the bridge to expand and contract. This means that if it gets heated up it expands. Hence, it needs a gap so it can expand and not break the road.
Thermal expansion:
Thermal expansion means "increase in size on heating". Various substances expand (increase in size) when their temperature is raised and contract (decrease in size) when their temperature is lowered.
Expansion of solids:
Whenever a solid in the form of a metal block is heated, it generally expands in length, breadth and height, so there will be expansion in volume. This kind of expansion of solid is called cubical expansion or volume expansion. However, if we heat a solid, which is in the form of a sheet (its thickness can be neglected as compared to its surface area), then the increase in area is called superficial expansion. Similarly, if we heat a solid, which is in the form of a wire (its cross–section area is too small compared to its length and hence can be neglected), then the increase in length is called linear expansion.