## What is Strain in Physics? | Definition, Formulas, Symbols, Types – Elasticity

Strain Definition in Physics:
1. The fractional change in configuration is called strain.

2. A strain is the response of a system to an applied stress. When a material is loaded with a force, it produces a stress, which then causes a material to deform.

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## What is Strain in Physics? | Definition, Formulas, Symbols, Types – Elasticity

Strain Formula:

Strain = $$\frac{\text { Change in configuration }}{\text { Original configuration }}$$

It has no unit and it is a dimensionless quantity.

Types of Strain in Physics:
According to the change in configuration, the strain is of three types:

• Longitudinal strain
• Volumetric strain
• Shearing strain

(i) Longitudinal strain Definition:
A longitudinal strain is defined as. Change in the length to the original length of an object. It is caused due to longitudinal stress and is denoted by the Greek letter epsilon ε.

Longitudinal strain Formula:

Longitudinal strain = $$\frac{\text { Change in length }}{\text { Original length }}$$
ε = $$\frac{ΔL}{L}$$

Where,
ε = Longitudinal strain
ΔL = Change in length
L = Original length

(ii) Volumetric strain Definition:
A Volumetric strain is defined as The volumetric strain is the unit change in volume, i.e. the change in volume divided by the original volume. volumetric strain is denoted by εvol.

Volumetric strain Formula:

Volumetric strain = $$\frac{\text { Change in volume }}{\text { Original volume }}$$
εvol = $$\frac{ΔV}{V}$$

Where,
εvol = Volumetric strain
ΔV = Change in volume
V = Original volume

(iii) Shear strain Definition:
1. Shearing strain is measured as a change in angle between lines that were originally perpendicular.

2. Shear strain is the ratio of displacement to an object’s original dimensions due to stress, and is the amount of deformation perpendicular to a given line rather than parallel to it.

Shearing strain = Angular displacement of the plane perpendicular to the fixed surface.

Shear Strain Symbol:
γ or ε

The Shear Strain Formula:

S = $$\frac{Δx}{X}$$

Where,
S = Shear Strain
Δx = change in dimension
X = original dimension

Elasticity:
Elasticity defines a property of an object that has the ability to regain its original shape after being stretched or compressed. Learn about the deforming force applied on an elastic object and how the stress and strain works on an object. What is a Hooke’s law and how it is applicable for the concept of elasticity.

## Critical Velocity | Definition, Formula, Units – Hydrodynamics

Critical Velocity Definition:
The critical velocity is the velocity of liquid flow, below which its flow is streamlined and above which it becomes turbulent.

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## Critical Velocity | Definition, Formula, Units – Hydrodynamics

Formula of Critical Velocity:

Critical velocity, vc = $$\frac{K \eta}{r \rho}$$

where,
K = Reynold’s number,
η = coefficient of viscosity of liquid,
r = radius of capillary tube and
ρ = density of the liquid.

Critical Velocity Dimensional Formula:

Vc = M0L1T-1

Unit of Critical Velocity:
SI unit of Critical Velocity is meter/sec

Hydrodynamics:
In physics, hydrodynamics of fluid dynamics explains the mechanism of fluid such as flow of liquids and gases. It has a wide range of applications such as evaluating forces and momentum on aircraft, prediction of weather, etc.

## State the Law of Floatation in Physics – Hydrostatics

Law of Floatation in Physics:
A body will float in a liquid, if the weight of the body is equal to the weight of the liquid displaced by the immersed part of the body.

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## State the Law of Floatation in Physics – Hydrostatics

The Three Laws of Floatation:
1. Density of the material of the body is less than or equal to the density of the liquid.
2. If density of material of body is equal to density of liquid, the body floats fully submerged in liquid in neutral equilibrium.
3. When body floats in neutral equilibrium, the weight of the body is equal to the weight of displaced liquid.

If W is the weight of the body and w is the buoyant force, then

1. If W > w, then body will sink to the bottom of the liquid.
2. If W < w, then body will float partially submerged in the liquid.
3. If W = w, then body will float in liquid if its whole volume is just immersed in the liquid.

The floating body will be in stable equilibrium, if meta-centre (centre of buoyancy) lies vertically above the centre of gravity of the body.

The floating body will be in unstable equilibrium, if meta-centre (centre of buoyancy) lies vertically below the centre of gravity of the body. The floating body will be in neutral equilibrium, if meta-centre (centre of buoyancy) coincides with the centre of gravity of the body.

Fraction of volume of a floating body outside the liquid

$$\left(\frac{V_{\text {out }}}{V}\right)=\left[1-\frac{\rho}{\sigma}\right]$$

where,
ρ = density of body
σ = density of liquid

If two different bodies A and B are floating in the same liquid, then

$$\frac{\rho_{A}}{\rho_{B}}=\frac{\left(v_{\text {in }}\right)_{A}}{\left(v_{\text {in }}\right)_{B}}$$

If the same body is made to float in different liquids of densities σA and σB respectively, then

$$\frac{\sigma_{A}}{\sigma_{B}}=\frac{\left(V_{\text {in }}\right)_{B}}{\left(V_{\text {in }}\right)_{A}}$$

Hydrostatics:
Hydrostatics is a property of liquid or fluid in mechanics. A fluid is a material which flows at room temperature, because its upper molecule overlaps the inner molecule, which tends to flow the liquid in forward direction. In hydrostatics, we will learn about the condition of fluids when it is in rest or exerted by an external force. Here we will study the fluids in motion.

## Angle of Contact in Surface Tension Definition, Formula and Examples – Physics

Define Angle of Contact:
The angle subtended between the tangents drawn at liquid surface and at the solid surface inside the liquid at the point of contact is called angle of contact (θ).

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## Angle of Contact in Physics | Definition – Surface Tension

If liquid molecules is in contact with solid (i.e. wall of capillary tube), then forces acting on liquid molecules are
(i) Force of cohesion Fc (acts at an angle 45° to the vertical)
(ii) Force of adhesion Fa (acts outwards at right angle to the wall of the tube)

Angle of contact depends upon the nature of the liquid and solid in contact and the medium which exists above the free surface of the liquid.

When wax is coated on a glass capillary tube, it becomes water-proof. The angle of contact increases and becomes obtuse. Water does not rise in it. Rather it falls in the tube by virtue of obtuse angle of contact.

• If θ is acute angle, i.e. θ<9o°, then liquid meniscus will be concave upwards.
• If θ is 90°, then liquid meniscus will be plane.
• If θ is obtuse, i.e. θ>9o°, then liquid meniscus will be convex upwards.
• If angle of contact is acute angle, i.e. θ<9o°, then liquid will wet the solid surface.
• If angle of contact is obtuse angle, i.e. θ>90°, then liquid will not wet the solid surface.

Angle of contact increases with increase in temperature of liquid. Angle of contact decreases on adding soluble impurity to a liquid.

• Angle of contact for pure water and glass is zero.
• For ordinary water and glass, it is 8°.
• For mercury and glass, it is 138°.
• For pure water and silver, it is 90°.
• For alcohol and clean glass θ = 0°.

Angle of Contact, Meniscus, and Shape of liquid surface

Surface Tension:
In Physics, the tension of the surface film of a liquid because of the attraction of the surface particles by the bulk of the liquid, which tries to minimize surface area is called surface tension. When the surface of the liquid is strong enough, then surface tension is applicable. It is strong enough to hold weight.

## Kinetic Theory of Ideal gases | Properties – Kinetic Theory of Gases

Kinetic Theory of Ideal Gases:
Kinetic theory of gases explains the behavior of gases, it correlates the macroscopic properties of gases e.g., Pressure, temperature etc., to the microscopic properties like speed, momentum, kinetic energy etc.

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## Kinetic Theory of Ideal gases | Properties – Kinetic Theory of Gases

Kinetic theory of gases, a theory based on a simplified molecular or particle description of a gas, from which many gross properties of the gas can be derived.

Microscopic and Macroscopic Properties in Thermodynamics:

Macroscopic Properties of Gases:

• Volume,
• Pressure, and
• Temperature

Microscopic Properties of Gases:

• speed,
• momentum,
• kinetic energy, etc.

Kinetic Theory of Gases:
In this concept, it is assumed that the molecules of gas are very minute with respect to their distances from each other. The molecules in gases are in constant, random motion and frequently collide with each other and with the walls of any container.

In this portion, you will learn about the properties of gases, based on density, pressure, temperature and energy. Continue reading here to learn more.

## Critical Temperature, Pressure and Volume – Kinetic Theory of Gases

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Critical Temperature, Pressure and Volume
Gases can’t be liquified above a temperature called critical temperature (TC) however large the pressure may be.

The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.

Critical Pressure Definition:
The pressure required to liquify the gas at critical temperature is called critical pressure (pC)
The critical pressure is the vapor pressure of a fluid at the critical temperature above which distinct liquid and gas phases do not exist.

Critical Volume Physics Definition:
The volume of the gas at critical temperature and pressure is called critical volume (VC).
The volume occupied by a certain mass, usually one gram molecule of a liquid or gaseous substance at its critical point: The numerical value of the critical volume depends upon the amount of gas under experiment.

Value of critical constants in terms of van der Waals’ constants a and b are as under

VC = 3b, pC = $$\frac{a}{27 b^{2}}$$ and TC = $$\frac{8 a}{27 R b}$$

Further, $$\frac{R T_{C}}{p_{C} V_{C}}=\frac{8}{3}$$ is called critical coefficient and is same for all gases.

Kinetic Theory of Gases:
In this concept, it is assumed that the molecules of gas are very minute with respect to their distances from each other. The molecules in gases are in constant, random motion and frequently collide with each other and with the walls of any container.

In this portion, you will learn about the properties of gases, based on density, pressure, temperature and energy. Continue reading here to learn more.

## What is the Ideal Gas Law? | Definition, Formula, Units – Kinetic Theory of Gases

Ideal or Perfect Gas Equation:
Perfect gas also called an ideal gas. Gases which obey all gas laws in all conditions of pressure and temperature are called perfect gases.

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## What is the Ideal Gas Law? | Definition, Formula, Units – Kinetic Theory of Gases

In most usual conditions (for instance at standard temperature and pressure), most real gases behave qualitatively like an ideal gas. Many gases such as nitrogen, oxygen, hydrogen, noble gases.

Ideal Gas Law Formula:
Ideal Gas Law or Equation of perfect gas

PV = nRT

where,
P = pressure,
V = volume,
T = absolute temperature,
R = universal gas constant and
n = number of moles of a gas.
Universal gas constant, R = 8.31 J mol-1K-1.

Ideal Gas Equation Units:
In SI units, p is measured in pa or N/m²
V is measured in cubic metres, (m³)
n is measured in moles, and
T in kelvins

Kinetic Theory of Gases:
In this concept, it is assumed that the molecules of gas are very minute with respect to their distances from each other. The molecules in gases are in constant, random motion and frequently collide with each other and with the walls of any container.

In this portion, you will learn about the properties of gases, based on density, pressure, temperature and energy. Continue reading here to learn more.

## Kinetic Theory of Gases Assumptions – Kinetic Theory of Gases

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Assumptions of Kinetic Theory of Gases:
1. Every gas consists of extremely small particles known as molecules. The molecules of a given gas are all identical but are different from those of another gas.

2. The molecules of a gas are identical spherical, rigid and perfectly elastic point masses.

3. Their molecular size is negligible in comparison to intermolecular distance (10-9m).

4. The speed of gas molecules lies between zero and infinity (very high speed).

5. The distance covered by the molecules between two successive collisions is known as free path and mean of all free path is known as mean free path.

6. The number of collisions per unit volume in a gas remains constant.

7. No attractive or repulsive force acts between gas molecules.

8. Gravitational attraction among the molecules is ineffective due to extremely small masses and very high speed of molecules.

9. The density of gas is constant at all points of the vessel.

10. The molecules of a gas keep on moving randomly in all possible directions with all possible velocities.

Kinetic Theory of Gases:
In this concept, it is assumed that the molecules of gas are very minute with respect to their distances from each other. The molecules in gases are in constant, random motion and frequently collide with each other and with the walls of any container.

In this portion, you will learn about the properties of gases, based on density, pressure, temperature and energy. Continue reading here to learn more.

## What is Brownian Motion in Physics? | Definition, Examples – Kinetic Theory of Gases

Brownian Motion Simple Definition:
The continuous random motion of the particles of microscopic size suspended in air or any liquid is called Brownian motion.

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## What is Brownian Motion in Physics? | Definition, Examples – Kinetic Theory of Gases

Brownian motion is observed with many kind of small particles suspended in both liquids and gases.

Brownian motion is due to the unequal bombardment of the suspended particles by the molecules of the surrounding medium.

Brownian Motion Examples

• The motion of pollen grains on still water.
• Movement of dust motes in a room (although largely affected by air currents)
• Diffusion of pollutants in the air.
• Diffusion of calcium through bones.

Kinetic Theory of Gases:
In this concept, it is assumed that the molecules of gas are very minute with respect to their distances from each other. The molecules in gases are in constant, random motion and frequently collide with each other and with the walls of any container.

In this portion, you will learn about the properties of gases, based on density, pressure, temperature and energy. Continue reading here to learn more.

## Mean Free Path Physics | Definition, Formula – Kinetic Theory of Gases

Mean Free Path Definition Physics:
The average distance travelled by a molecule between two successive collisions is called mean free path (λ).

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## Mean Free Path Physics | Definition, Formula – Kinetic Theory of Gases

Mean Free Path Formula Physics:
Mean free path is given by

λ = $$\frac{k T}{\sqrt{2} \pi \sigma^{2} p}$$

where,
σ = diameter of the molecule,
p = pressure of the gas,
T = temperature and
k = Boltzmann’s constant.

Mean free path, λ ∝ T and

Mean Free Path is Inversely Proportional to,

λ ∝ $$\frac{1}{p}$$

### Mean Free Path in Kinetic Theory of Gases

On the basis of kinetic theory of gases, it is assumed that the molecules of a gas are continuously colliding against each other. Mean Free Path is the average distance traversed by molecule between two successive collisions.

Kinetic Theory of Gases:
In this concept, it is assumed that the molecules of gas are very minute with respect to their distances from each other. The molecules in gases are in constant, random motion and frequently collide with each other and with the walls of any container.

In this portion, you will learn about the properties of gases, based on density, pressure, temperature and energy. Continue reading here to learn more.