Ch 7Properties of Matter — Class 11 Physics, concept-first.

One of the oldest surviving dams in the world is the Kallanai, built across the river Kaveri near Tiruchirappalli to hold back and direct floodwater for irrigation.

Everything in the universe is made of atoms, yet the same substance can exist as a solid, a liquid, or a gas -- water as ice, liquid water, or steam is the standard example, even though all three form…

In a solid, interatomic forces of attraction and repulsion hold every pair of neighbouring atoms at a particular equilibrium separation -- their mean positions.

STRESS. When a deforming force is applied to a body, the shape or size (or both) can change because the relative positions of its constituent atoms or molecules shift.

HOOKE'S LAW states that, for a small deformation within the elastic limit, the strain produced in a body is directly proportional to the stress that produces it -- equivalently, as long as the elastic…

Within the elastic limit, since stress is proportional to strain, the ratio is a constant for a given material -- this constant is called the MODULUS OF ELASTICITY of that material.

When a wire is stretched, it does not simply get longer -- it also gets thinner: its length increases (an elongation, or longitudinal strain) while its diameter simultaneously decreases (a contraction…

When a wire is stretched, work is done against the internal restoring force, and this work is stored in the wire as ELASTIC POTENTIAL ENERGY (also simply called elastic energy).

The elastic behaviour of materials, and specifically how much a beam bends under a given load, is a major structural-engineering concern for the stability of buildings and bridges.

Fluids -- liquids and gases together -- are found everywhere: roughly two-thirds of the Earth's surface is covered by water, and the atmosphere of air envelops the whole planet.

PRESSURE OF A FLUID. A fluid is a substance that begins to flow when even a very small external force is applied to it -- it offers very little resistance to deformation.

The pressure a mountaineer feels DECREASE with altitude and the pressure a diver feels INCREASE with depth are both examples of HYDROSTATIC PRESSURE -- pressure due to a static fluid.

PASCAL'S LAW, discovered by the French scientist Blaise Pascal, states that a change in pressure applied at any point of an enclosed liquid at rest is transmitted UNDIMINISHED to every other point of…

When a body is partially or fully immersed in a fluid, it pushes aside (displaces) a certain volume of that fluid, and the displaced fluid in turn exerts an UPWARD force on the body, opposing its weig…

Sections 7.2 and 7.3 dealt with matter that is essentially static (a deformed solid returning to rest, a fluid sitting still in a container). This section turns to fluids that are actually MOVING.

Consider a liquid flowing steadily over a fixed horizontal layer, with the flow speed increasing uniformly the further a layer is from that fixed bottom layer.

The flow of a fluid can happen in several distinct ways -- steady (streamlined) or turbulent, compressible or incompressible, viscous or non-viscous.

When the speed of a moving fluid exceeds its critical speed , the motion becomes TURBULENT. In turbulent flow, the velocity of the fluid at a given location changes both in magnitude AND in direction…

Osborne Reynolds (1842-1912) worked out how to predict, in advance, whether the flow of a fluid through a cylindrical pipe will be streamlined or turbulent, by combining the relevant physical quantiti…

Consider a small metallic sphere released from rest and falling freely through a large column of a highly viscous fluid.

Stoke performed experiments on the motion of small spherical bodies through different fluids and found that the viscous force F acting on a spherical body of radius r depends directly on (i) the radiu…

Poiseuille analysed the steady flow of a liquid through a narrow capillary tube and worked out an expression for the volume of liquid flowing through it per second, under these conditions: the flow th…

Viscosity governs a wide range of practical, everyday choices and technologies. (1) A lubricant used for heavy machinery parts must have a HIGH coefficient of viscosity, and choosing the right lubrica…

Liquids, unlike solids, have no fixed shape of their own, but they DO have a fixed volume -- so whenever a liquid is poured into a container, it always presents a FREE SURFACE (the boundary between th…

The molecules of a liquid, unlike those of a solid, are not rigidly fixed in place -- they are free to move about relative to one another.

Surface tension is not a fixed, unchanging property of a liquid -- it varies with several factors. (1) CONTAMINATION: the presence of any contamination or impurity on a liquid's surface affects its su…

SURFACE ENERGY. Inside a liquid, a molecule is pulled equally in all directions by its neighbours; but near the surface, a molecule is pulled predominantly downward (only by molecules below it), so th…

When the free surface of a liquid meets a solid surface, the liquid surface becomes CURVED right at the point of contact, and the angle at which it meets the solid becomes an important physical quanti…

The free surface of a liquid becomes curved on contact with a solid, and the degree of curvature depends on the nature of the liquid-air or liquid-gas interface involved, through the interfacial surfa…

The word 'capilla' means hair in Latin, and a tube with a very fine, hair-thin bore is accordingly called a CAPILLARY TUBE.

SURFACE TENSION BY THE CAPILLARY RISE METHOD. The fundamental cause of a liquid rising up a narrow tube is the pressure difference across the curved liquid-air interface (the influence of gravity on t…

Surface tension has a wide range of practical applications and effects. Pouring a small amount of oil onto standing water breaks the water's elastic surface film by lowering its surface tension there;…

This final section of the unit turns to fluids in a genuinely dynamic situation -- a fluid actually flowing through a pipe -- and asks how mass, and then energy, are conserved as it does so.

To discuss the mass flow rate of a fluid through a pipe, the flow is first assumed to be STEADY: at any given point in the pipe, the velocity of every fluid particle passing through it remains constan…

As it flows steadily, a liquid can possess three distinct kinds of energy simultaneously: kinetic energy, potential energy, and pressure energy.

In 1738, the Swiss scientist Daniel Bernoulli worked out a relationship for the flow of a fluid through a pipe of varying cross section, based on the streamlined flow of a liquid and the law of conser…

SUMMARY. The interatomic force between the atoms of an element, and the intermolecular force between the molecules of a compound, are the microscopic forces underlying every macroscopic property cover…

The chapter closes with a graded four-part EVALUATION. Part I is fifteen Multiple Choice Questions, several explicitly drawn from NEET question banks (NEET model 2018, NEET 2014 model), covering stres…

Sample papers and previous-year board questions for this subject.