PHYSICS : PROPERTIES OF MATTER
Matter: Matter is considered as any thing which has weight and occupy
It exist in three states: Solid, liquid and gas. In solid, molecules vibrate about fixed positions. In liquid, molecules also vibrate but simultaneously they move freely throughout the material. In gas, the molecules are much farther apart than in solids and liquids and move at high velocities.
Interatomic Forces: The electrostatic force of interaction acting between the two or more atoms is called interatomic forces. The range of interatomic forces is equal to the order of atomic size, i.e. m. A force which changes the configuration of a body, is called a deforming force.
Solid: It is that, state of matter which has definite shape and definite volume. In this state molecules are very closely packed.
Properties of Solids
Elasticity: The property of a body by virtue of which it regain its original configuration after the removal of deforming force, is called elasticity. Quartz and phosphor bronze are almost perfectly elastic bodies.
Plasticity: The property of a body by virtue of which it does not regain its original configuration after the removal of deforming force, is called plasticity.
Stress: The internal restoring force acting per unit area of
crosssection of a deformed body, is called stress.
Stress is of two types
- Normal stress
- Tangential stress
The maximum deforming force upto which a body retains its property of
elasticity is called the limit of elasticity of the material body.
The minimum stress required to break a wire is called breaking stress.
The torque required to produce a given twist in a hollow cylinder is greater than that required to produce the same twist in a solid cylinder. Therefore, hollow shaft is stronger than a solid shaft.
Springs are made of steel, not of copper as Young's modulus of elasticity of steel is more than that of copper.
Elastic Limit: It is the limit of stress and strain upto which a wire remains elastic.
Plastic Behaviour: If the wire is stretched beyond the elastic limit, the strain increases much more rapidly. If the stretching force is removed, the wire does not comes back to its natural length.
Fracture Point: If the deformation is increased further the plastic behaviour, the wire breaks at a point known as fracture point.
Ductile and Brittle Materials: If large deformation takes place between the elastic limit and the fracture point, the material is called ductile. If the wire breaks soon after the elastic limit is crossed, it is called brittle.
Elastic Fatigue: It is the property of an elastic body by virtue of which its behaviour becomes less elastic under the action of repeated alternating deforming force. Due to elastic fatigue, the bridges becomes less elastic after a use of long time and therefore are declared unsafe.
Atmospheric Pressure: The pressure exerted by the atmosphere, is called atmospheric pressure. Aneroid barometer is used to measure atmospheric pressure and height of a place. Other units of atmospheric pressure are torr and bar.
Pascal's Law: The pressure exerted anywhere at a point of confined fluid is transmitted equally and undiminished, in all directions throughout the liquid. Hydraulic lift, hydraulic press hydraulic brakes works on the basis of Pascal's law.
Buoyancy: When a body is partially or wholly immersed in a liquid, an upward force acts on it, which is called buoyant force or upthrust and this property of fluids is called buoyancy. Buoyant force is equal to the weight of the liquid displaced by the submerged part of the body.
The buoyant force acts at the centre of gravity of the quid displaced by the submerged part of the body, which is called 'centre of buoyancy'.
Archimedes Principle: When a body is partially or completely immersed in a quid, it loses some of its weight. The loss in weight is equal to the weight of the liquid displaced by the submerged part of the body.
Surface Tension: The property of a liquid by virtue of which it tries to minimise its free surface area is called surface tension. The minimum surface area of a given amount of liquid is for spherical shape. Therefore, rain drops are spherical.
Factors Affecting Surface Tension: Temperature The surface tension of
a liquid decreases withincrease in temperature.
Soluble Impurities: If the impurities are less soluble in liquid, then its surface tension decreases. If impurities are highly soluble in liquid, then its surface tension increases.
Applications of Surface Tension: Surface tension of a liquid becomes zero at critical temperature. When soap, detergent, dettol, phenyl etc., are mixed in water then its surface tension decreases. When salt is added in water, its surface tension increases. When oil spreads over the surface of water, its surface tension decreases.
- When kerosene oil is sprinkled on water, its surface tension decreases. As a result the larva of mosquitoes floating on the surface of water die due to sinking.
- Warm soup is tasty because at high temperature its surface tension is low and consequently the soup spreads on all parts of the tongue.
- Antiseptics like dettol have low surface tension and therefore it reaches in the tiny cracks of the wound and cleans the germs and bacteria.
- The surface tension of soap solution in water is less than the surface tension of pure water. Therefore, soap solution cleans greasy strains of clothes better than pure water.
Capillarity: The phenomenon of rising or falling of liquid column in a capillary tube (glass tube of very fine bore) is called capillarity.
Illustrations of capillarity
1. A piece of blotting paper soaks ink because the pores of the blotting paper serve as capillary tubes.
2. The oil in the wick of a lamp rises due to capillary action of threads in the wick.
3. The root hairs of plants draws water from the soil through capillary action.
4. To prevent loss of water due to capillary action, the soil is loosened and split into pieces by the farmers.
5. If a capillary tube is dipped in water in an artificial satellite, water rises up to other end of tube because of its zero apparent weight, how long the tube may be.
6. Action of towel in soaking up water from the body is due to capillary action of cotton in the towel.
7. Melted wax, in a candle rises up to wick by capillary action.
Cohesive and Adhesive Forces: The intermolecular force of attraction acting between the molecules of same substance is called cohesive force. e.g., Intermolecular force of attraction acting between the molecules of water, mercury etc. The intermolecular force of attraction acting between the molecules of different substance is called adhesive force. e.g., Intermolecular force of attraction acting between the molecules of paper and gum, paper and ink, etc.
Viscous force: The force which opposes the relative motion between
different layers of liquid or gases is called viscous force.
Viscosity: Viscosity is the property of a liquid by virtue of which it opposes the relative motion between its different layers.
Viscosity is the property of liquids and gases both.
The viscosity of a liquid is due to cohesive force between its molecules.
The viscosity of a gas is due to diffusion of its molecules from one layer to other layer.
Viscosity of gases is much less than that of liquids. There is no viscosity in solids.
Viscosity of an ideal fluid is zero.
With rise in temperature, viscosity of liquids decreases and that for gases increases.
Viscosity of a fluid is measured by its coefficient of viscosity. Its SI unit is decapoise (kg/ms) or pascal second. It is generally denoted by η.
Stoke's Law: According to this law, the viscous force depends upon the coefficient of viscosity, velocity of the moving object and its size.
Terminal Velocity: When a small spherical body falls through a long liquid column its velocity increases gradually but later on it becomes constant, called terminal velocity. The radius of spherical rain drops is very small therefore their terminal velocity is also small, with which they strike the earth’s surface. When a liquid flow through a pipe, its speed i maximum near axis and minimum near the walls of the pipe.
Equation of Continuity: When a non-viscous liquid flows through a pipe of nonuniform cross-sectional area in stream-lined flow, (i.e. velocity at every point in the fluid remains constant) then at each section of the tube, the product of area of cross-section of the pipe and velocity of liquid remains constant, i.e. A × v = constant.
Therefore speed (v) of fluid flow becomes faster in narrower pipe.
Bernoulli's Theorem: If a non-viscous and incompressible liquid is flowing in stream-lined flow then total energy, i.e., sum of pressure energy, kinetic energy and potential energy, per unit volume of the liquid remains constant. Venturi tube and aspirator pump works on Bernoulli’s theorem. According to Bernoulli's theorem, with increase in velocity of quid its pressure decreases and vice-versa. During storms or cyclones, the roofs of the huts or tinned roofs blown off because wind blows with very high speed over the top of the roof and therefore pressure of air decreases. Due to the pressure difference of air above and below the roof, a lifting force acts on the roof. If it is sufficient to balance the weight of the roof it start to fly off.
Magnus Effect : Motion of a Spinning Ball When swing bowlers deliver the ball, the ball changes its plane of motion in air.