NEET Study Notes on Properties of Bulk Matter: Stress is defined as the internal restoring force that acts per unit area on a deformed body. Strain is the ratio of change in size and shape of the body with respect to the original shape and size of the body. In 1679, Robert Hooke gave Hooke’s law which states that within elastic limit or stress is directly proportional to strain.
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Topics | Sub-Topics |
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Properties of Bulk Matter |
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Elasticity
Stress
where S.I. unit is Nm-2
Strain
The amount of change in shape and size in the original with respect to the original size and shape is called strain.
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In 1679, Robert Hooke has given the Hooke’s Law, which states that stress is directly proportional to the strain
i.e. Stress ∝ strain
Where this constant proportionality is called modulus of electricity or coefficient of electricity
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Consider a long bar of cross-sectional area A with length l0 which is tied at one end. When external force Fl is applied longitudinally along the bar internal forces in the bar resist distortion, the bar then attains equilibrium in which length is greater than and external force is balanced by internal forces. The bar is stressed in this position.
Young’s Modulus measures the resistance of a solid to elongation where Y is defined as the
where ΔI is change in length of the bar when Fl is applied
Shear Modulus or the modulus of rigidity which is represented by η measures the resistance to motion of the plane of a sliding solid part
There is no change in volume. However, there is a change in shape
Poisson’s Ratio is Lateral strain/longitudinal strain
Theoretical value of Poissons’s ratio ranges between -1 and 0.5 whereas the practical value of Poisson’s ratio lies between 0 and 0.5
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Viscosity- Internal Friction of Fluid that opposes relative motion between different layers of fluid is called viscosity.
The viscous force between layers of fluid with gradient velocity ()
Is
where η is the coefficient of viscosity
Reynold’s Number is represented by N which is the pure number that determines the nature of liquid flow through a pipe.
The sum of pressure, kinetic energy, and potential energy per unit volume remain constant in the nonviscous, streamlined flow of liquids.
i.e., + gh +v2 = constant
Where p- density of fluid
h-0
then
The flow of liquids can be of four types- streamline motion, steady-state motion, laminar motion, and turbulent motion
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The motion of a solid is opposed by viscous force depending on velocity, shape, and size of the body. To overcome this vicious force, the energy of the body constantly decreases.
where r is the radius of the spherical body
v is the velocity
Η is the viscosity
Surface Tension is defined as the force per unit length that acts at right angles of an imaginary line’s either side that is drawn on the free surface of the liquid.
Angle between the tangent to the liquid surface and the tangent to the solid surface is at the point of contact is called the Angle of contact. The value of angle of contact of some solids and liquids are tabulated below:
Surface Pair | Angle of Contact |
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Pure Water and Glass | 0° |
Silver and Glass | 90° |
Alcohol and glass | 138° |
Normal water and glass | 8° |
Mercury and glass | 135° |
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The physical quantity that indicates the hotness or coldness of a body is called temperature. When the heat does not flow from one body to another the bodies are said to be at the same temperature or in a position of thermal equilibrium.
Linear Expansion is the increase in length with an increase in temperature.
where l0 is the initial length
L is the final length
ΔT is the change in temperature
α is the coefficient of linear expansion
Water has a negative coefficient of expansion in volume within the temperature ranging from 0 to 4 Celsius. As a result water contracts when the temperature increases from 0 Celsius to 4 celsius. At 4 Celsius, the density of water is 1000 kg m–3. This is known as anomalous behavior of water.
The amount of heat that is required to raise the temperature of the substance by 1 degree. It is represented by
The value of specific heat of gas may be positive or negative and may vary between zero to infinity.
As per Mayer’s Relation CP – CV = R, where R is a gas constant
Gas being heated at constant pressure leads to expansion of gas due to work done as well as an increase in temperature. Hence CP > CV
There are three modes of heat transfer:
The rate of heat flow is given by
where
K is the thermal conductivity (proportionality constant) which helps in measuring how heat energy is quickly conducted through the substance.
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The process of heat transfer through the movement of particles from one medium to another is known as convection. This happens due to the difference in density.
The process by which heat is transferred without any medium from one place to another is called Radiation. Light Radiation from the sun to earth reaches through Radiation Process.
According to Stefan Boltzmann, the power radiated from a black body for overall wavelength is proportional to the thermodynamic temperature of fourth power T.
for a perfectly black body
where E is the energy transmitted per second from the unit surface area of a black body
T is the temperature
σ is Stefan’s Constant
σ- 5.67×10–8 Wm–2 K–4.
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According to Newton’s Law of Cooling, the rate at which heat of a body is lost is directly proportional to the difference in temperature between the body and its surroundings.
where T is the temperature of the body
T0 Is the temperature of the surroundings
and
Where e is the emissivity of the body
A is the area of the surface of the body
σ is Stefan’s Constant
m is the mass of the body
c is the specific heat of the body
This relationship is possible when there is not much difference between the temperature of the body and temperature of the surroundings.
Question: What does the stress vs strain curve depend on?
Answer: Relationship between stress and strain
Question: On the application of force on the body, due to deformation, a restoring force develops on the body. What is this restoring force per unit area called?
Answer: Stress
Question: What does the modulus of elasticity depend upon?
Answer: None of the above
Question: What is the total modulus of elasticity?
Answer: Three
Question: What does Hooke’s Law define?
Answer: Modulus of Elasticity
Question: What is k in the relation stress= k×strain?
Answer: modulus of elasticity
Question: Why are raindrops spherical?
Answer: Surface tension forces
Question: What is the property of a liquid that opposes relative motion between different layers?
Answer: Viscosity
Question: What is specific volume a reciprocal of?
Answer: mass density
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