### PHYSICS (FLUID: WITH INTERESTING KNOWLEDGE)

A substance which begins to flow under an external force is called a fluid. Liquids and gases are fluids.

### FLUIDDENSITY

The ratio of mass to the volume of a body is called its density. (i.e. mass present in its unit volume). It is a scalar quantity having SI unit kg/m3.
EXAMPLE: The density of water is 1000 kg/m3. The density of water is maximum at 4°C.

### HYDROMETER

It is an instrument used to measure the density or relative density of a liquid. Its working is based on the law of floatation.

### FLUID PRESSURE

Thrust (the normal force) exerted by a liquid per unit area of the surface in contact at rest, it is called fluid pressure.
Fluid pressure (p) = F/A
Its unit is N/m2 or Pascal (Pa).

### ATMOSPHERIC PRESSURE

The pressure exerted by the atmosphere is called atmospheric pressure. An aneroid    barometer is used to measure the 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 the 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. The buoyant force is equal to the weight of the liquid displaced by the submerged part of the body.

### 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.

### LAW OF FLOATATION

A body will float in a liquid if the weight of the body is equal weight of the liquid displaced by the immersed part of the body. In floating condition, the center of gravity (g) and the center of buoyancy (B) of the floating body must lie on the same straight line. Ice and large icebergs float on water surface as its density (0.92 g/cm3) is lesser than the density of water.

It is easier to swim in sea water than in a river as density of sea water is greater than the density of river water. In sea water, buoyant force is greater than that in river water. The density of human body is less than the density of water but the density of human head is greater than the density of water. Therefore, during swimming a person displaces the liquid with hands and legs and total weight of displaced liquid becomes equal to the weight of the body.

### SURFACE TENSION

The property of a liquid by virtue of which it tries to minimize 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 with increase 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.

#### Temperature

The surface tension of a liquid decreases with increase in temperature.

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, it's surface tension increases.
• When oil spreads over the surface of water, it's surface tension decreases.
• When kerosene oil is sprinkled on water, it's 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 it's 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.

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 the capillary action of threads in the wick.
3. The root hairs of plants draw 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, the water rises up to other end of tube because of its zero apparent weight, how long the tube may be.
6. The action of a towel in soaking up water from the body is due to the capillary action of cotton in the towel.
7. Melted wax, in a candle, rises up to wick by capillary action.

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 the cohesive force between its molecules.
• The viscosity of a gas is due to diffusion of its molecules from one layer to another layer.
• Viscosity of gases is much less than that of liquids.
• There is no viscosity in solids.
• The viscosity of an ideal fluid is zero.
• With the rise in temperature, the 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 Î·.

### 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 raindrops is very small therefore their terminal velocity is also small, with which they strike the earth’s surface. When a liquid flows through a pipe, its speed is maximum near axis and minimum near the walls of the pipe.

### EQUATION OF CONTINUITY

When non-viscous liquid flow through a pipe of non-uniform 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 the 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 a 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 liquid 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 starts to fly off.

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### HISTORY (MUGHAL EMPIRE)

BABUR Descendent of Timur (from his father side) and Genghis khan (from his mother side) It is said that he was invited in India by Daulat Khan Lodi and Alam kha lodi He laid the foundation of the Mughal empire by defeating Ibrahim Lodi in the first battle of Panipat on 21, April 1526. In 1527, he defeated Rana Sanga of Mewar at Khanwa. In 1528, he defeated Medini Rai of Chaneri at Chanderi. In 1529, he defeated Muhammad Lodhi (uncle of Ibrahim Lodhi) at Ghaghra. In 1530, he died at Agra. His tomb is at Lahore. The tomb of only two Mughal emperors are outside India i.e. Babur & Bahadur Shah Zafar He was the first to use gunpowder & artillery in India. Two gun masters Mustafa & Ustad Ali were in his army He wrote his autobiography Tuzuk-i-Baburi in Turki. Tuzuk-i-Baburi was translated in Persian (named Baburnama) by Abdur Rahim Khan-e-khana & in English by Madan Bebridge. He compiled two anthologies of poems, Diwan (in Tu

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Think like a proton and stay positive Sound waves are mechanical longitudinal waves and require a medium for their propagation. Sound cannot propagate through vacuum. When it propagates, speed and wavelength changes but the frequency remain constant. It is of three types Infrasonic waves – (0 to 20 Hz) Audible waves – (20 to 20,000 Hz) Ultrasonic waves – (>20,000 Hz) Properties of Sound Wave Reflection The bouncing back of sound when it strikes a hard surface, is called reflection of sound. The laws of reflection of light are also obeyed during reflection of sound. The working of megaphone, soundboards, and ear trumpets are based on the reflection of sound. The repetition of sound due to reflection of sound waves, is called an echo. The minimum distance from a sound-reflecting surface to hear an echo is nearly 17 m. The persistence of hearing on the human ear is 1/10th of a second. Soundproof rooms are made of

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The only way to learn  MATHEMATICS  is to do  MATHEMATICS Trigonometry , the branch of  mathematics  concerned with specific functions of  angles  and their application to calculations. There are six functions of an angle commonly used in trigonometry. Their names and abbreviations    sine  (sin),  cosine  (cos),  tangent  (tan),  cotangent  (cot),  secant  (sec), and  cosecant  (csc). The word  trigonometry  comes from the Greek words  trigonon  (“triangle”) and  metron (“tomeasure”). The first use of the idea of ‘sine’ in the way we use  it today was in the work Aryabhatiyam by Aryabhata,  in A.D. 500. Aryabhata used the word ardha-jya  for the half-chord, which was shortened to jya or  jiva in due course. When the Aryabhatiyam was  translated into Arabic, the word jiva was retained as  it is. The word jiva was translated into sinus, which  means curve, when the Arabic version was translated  into Latin. Soon the word sinus , also used as sine ,  became comm

### MATH MENSURATION 2-D

The only way to learn MATHEMATICS is to do MATHEMATICS IF YOU HAVE KNOWLEDGE LET OTHERS  CANDLE LIGHT  IN IT https://www.correcteducate.com/2019/08/chemistry-base-and-salts.html https :// www . correcteducate . com / 2019 / 07 / root - word . html https :// www . correcteducate . com / 2019 / 07 / properties - of - quadrilaterals . html https :// www . correcteducate . com / 2019 / 07 / geography - universe . html https://www.correcteducate.com/2019/07/general-knowledge.html https://www.correcteducate.com/2019/07/vocabulary-series_29.html

### HISTORY (ONE LINER INCIDENTS OF 20th CENTURY)

One-liner knowledgeable modern Indian history incidents, that rapidly boost your memory 1905 --> Partition of Bengal by Lord Curzon, swadeshi movement, Rakhi diwas                  (by Rabindranath Tagore) 1906 --> Muslim league was founded by Aga Khan, Salim Ullah in Dhaka 1907 --> Congress split, Tata steel established 1908 --> Swadeshi stopped, first-time Gandhiji went to jail 1909 --> Morley-Minto reforms 1911 --> Delhi darbar, Bengal partition revoked 1912 --> 23 December, Delhi became capital of British empire in India 1913 --> Gadar party, Rabindranath Tagore won Nobel prize 1914 --> World war I started 1915 --> 9, January 1915 Gandhiji Returned to India, NRI Day is celebrated on this   day every year 1916 --> Lucknow pact, Home rule league, Gandhiji established Sabarmati Ashram 1917 --> Champaran satyagraha 1918 --> Ahmedabad Mill Strike, Kheda Satyagragh, Montague Chelmsford refor