Fluids

Class 9 | Science — Physics | Unit 3

Class 9 Unit 3 Science

UNIT 3 FLUIDS

Learning Objectives

After completing this lesson, students will be able to

• define pressure in terms of weight.
• explain the variation of pressure with respect to depth in a fluid.
• learn the fact that liquid exerts an upward force on objects immersed in it.
• calculate the density of a liquid when pressure and altitude are given.
• learn the formula for finding the relative density of an object and apply the same.
• understand the behaviour of floating bodies.

Introduction

A small iron nail sinks in water, whereas a huge ship of heavy mass floats on sea water. Astronauts have to wear a special suit while travelling in space. All these have a common reason called 'pressure'. If the pressure increases in a solid, based on its inherent properties, it experiences tension and ultimately deforms or breaks. In the case of fluids it causes them to flow rather than to deform. Although liquids and gases share some common characteristics, they have many distinctive characteristics on their own. It is easy to compress a gas whereas liquids are incompressible. Learning of all these facts helps us to understand pressure better. In this lesson you will study about pressure in fluids, density of fluids and their application in practical life.

3.1 Thrust and Pressure

Pushing a pin into a board by its head is difficult. But pushing it by the pointed end is easy. Why? Have you ever wondered why a camel can run in a desert easily? Why a truck or a motorbus has wider tyre? Why cutting tools have sharp edges? In order to answer these questions and understand the phenomena involved, we need to learn about two interrelated physical concepts called thrust and pressure.

Activity 1

Stand on loose sand. Your feet go deep into the sand. Now, lie down on the sand. What happens? You will find that your body will not go that deep into the sand. Why?

In both the cases of the above activity, the force exerted on the sand is the weight of your body which is the same. This force acting perpendicular to the surface is called thrust. When you stand on loose sand, the force is acting on an area equal to the area of your feet. When you lie down, the same force acts on an area of your whole body, which is larger than the area of your feet. Therefore, the effect of thrust, depends on the area on which it acts. The effect of thrust on sand is larger while standing than while lying. The force per unit area acting on an object concerned is called pressure. Thus, we can say thrust on an unit area is pressure.

Pressure Formula

Pressure = thrust ÷ area of contact

For the same given force, if the area is large pressure is low and vice versa.

In SI units, the unit of thrust is newton (denoted as N). The unit of pressure is newton per square metre or newton metre⁻² (denoted as Nm⁻²). In the honour of the great French scientist, Blaise Pascal, 1 newton per square metre is called as, 1 pascal denoted as Pa.

1 Pa = 1 N m⁻²

Do You Know?

If a single nail pricks our body it is very painful. How is it possible for people to lie down on a bed of nails, still remain unhurt? It is because, area of contact is more.

Problem 1

A man whose mass is 90 kg stands on his feet on a floor. The total area of contact of his two feet with the floor is 0.036 m² (Take, g = 10 m s⁻²). How much is the pressure exerted by him on the floor?

Solution:

The weight of the man (thrust), F = mg = 90 kg × 10 m s⁻² = 900 N

Pressure, P = F ÷ A = 900 N ÷ 0.036 m² = 25000 Pa

3.2 Pressure in Fluids

All the flowing substances, both liquids and gases are called fluids. Like solids, fluids also have weight and therefore exert pressure. When filled in a container, the pressure of the fluid is exerted in all directions and at all points of the fluid. Since the molecules of a fluid are in constant, rapid motion, particles are likely to move equally in any direction. Therefore, the pressure exerted by the fluid acts on an object from all directions.

Fluid Pressure Formula

Fluid Pressure = total force exerted by the fluid ÷ area over which the force is exerted = F ÷ A

We shall first learn about the pressure exerted by liquids and then learn about the pressure exerted by gases.

3.2.1 Pressure due to liquids

The force exerted due to the pressure of a liquid on a body submerged in it and on the walls of the container is always perpendicular to the surface. When an air filled balloon is immersed inside the water in a vessel it immediately comes up and floats on water. This shows that water (or liquid) exerts pressure in the upward direction.

Similarly, liquid pressure acts in lateral sides also. When a bottle having water is pierced on the sides we can see water coming out with a speed. This is because liquid exerts lateral pressure on the walls the container.

Activity 2

Take a transparent plastic pipe. Also take a balloon and tie it tightly over one end of the plastic pipe. Pour some water in the pipe from the top. What happens? The balloon tied at the bottom stretches and bulges out. It shows that the water poured in the pipe exerts a pressure on the bottom of its container.

3.2.2 Factors determining liquid Pressure in liquids

Pressure exerted by a liquid at a point is determined by,

1. depth of the liquid (h)
2. density of the liquid (ρ)
3. acceleration due to gravity (g)

Activity 3

Take a large plastic can. Punch holes with a nail in a vertical line on the side of the can as shown in figure. Then fill the can with water. The water may just dribble out from the top hole, but with increased speed at the bottom holes as depth causes the water to squirt out with more pressure.

From this activity we can infer that pressure varies as depth increases. But, it is same at a particular depth independent of the direction.

Activity 4

Take two liquids of different densities say water and oil to a same level in two plastic containers. Make holes in the two containers at the same level. What do you see? It can be seen that water is squirting out with more pressure than oil. This indicates that pressure depends on density of the liquid.

3.2.3 Pressure due to a liquid column

A tall beaker is filled with liquid so that it forms a liquid column. The area of cross section at the bottom is A. The density of the liquid is ρ. The height of the liquid column is h. In other words the depth of the water from the top level surface is 'h'.

We know that, thrust at the bottom of the column (F) = weight of the liquid.

Therefore, F = mg ... equation (1)

We can get the mass of the liquid by multiplying the volume of the liquid and its density.

Mass, m = ρV ... equation (2)

Volume of the liquid column, V = Area of cross section (A) × Height (h) = Ah ... equation (3)

Substituting (3) in (2)

Mass m = ρAh ... equation (4)

Substituting (4) in (1)

Force = mg = ρAhg

Pressure, P = thrust (F) ÷ Area (A) = mg ÷ A = ρ(Ah)g ÷ A = ρhg

Pressure due to a liquid column

P = hρg

This expression shows that pressure in a liquid column is determined by depth, density of the liquid and the acceleration due to gravity. Interestingly, the final expression for pressure does not have the term area A in it. Thus, pressure in liquid depends on depth only.

Problem 2

Calculate the pressure exerted by a column of water of height 0.85 m (density of water, ρw = 1000 kg m⁻³) and kerosene of same height (density of kerosene, ρk = 800 kg m⁻³)

Solution:

Pressure due to water = hρwg = 0.85 m × 1000 kg m⁻³ × 10 m s⁻² = 8500 Pa

Pressure due to kerosene = hρkg = 0.85 m × 800 kg m⁻³ × 10 m s⁻² = 6800 Pa

3.3 Atmospheric pressure

Earth is surrounded by a layer of air up to certain height (nearly 300 km) and this layer of air around the earth is called atmosphere of the earth. Since air occupies space and has weight, it also exerts pressure. This pressure is called atmospheric pressure. The atmospheric pressure we normally refer is the air pressure at sea level. Air gets 'thinner' with increasing altitude. Hence, the atmospheric pressure decreases as we go up in mountains. On the other hand air gets heavier as we go down below sea level like mines.

Do You Know?

Human lung is well adapted to breathe at a pressure of sea level (101.3 kPa). As the pressure falls at greater altitudes, mountain climbers need special breathing equipments with oxygen cylinders. Similar special equipments are used by people who work in mines where the pressure is greater than that of sea level.

3.3.1 Measurement of atmospheric pressure

The instrument used to measure atmospheric pressure is called barometer. A mercury barometer, first designed by an Italian Physicist Torricelli, consists of a long glass tube (closed at one end, open at the other) filled with mercury and turned upside down into a container of mercury. This is done by closing the open end of the mercury filled tube with the and then opening it after immersing it in to a trough of mercury.

The barometer works by balancing the mercury in the glass tube against the outside air pressure. If the air pressure increases, it pushes more of the mercury up into the tub and if the air pressure decreases, more of the mercury drains from the tube. As there is no air trapped in the space between mercury and the closed end, there is vacuum in that space. Vacuum cannot exert any pressure. So the level of mercury in the tube provides a precise measure of air pressure which is called atmospheric pressure. This type of instrument can be used in a lab or weather station.

On a typical day at sea level, the height of the mercury column is 760 mm. Let us calculate the pressure due to the mercury column of 760 mm which is equal to the atmospheric pressure. The density of mercury is 13600 kg m⁻³.

Pressure, P = hρg = (760 × 10⁻³ m) × (13600 kg m⁻³) × (9.8 m s⁻²) = 1.013 × 10⁵ Pa

This pressure is called one atmospheric pressure (atm). There is also another unit called (bar) that is also used to express such high values of pressure.

1 atm = 1.013 × 10⁵ Pa

1 bar = 1 × 10⁵ Pa

Hence, 1 atm = 1.013 bar.

Expressing the value in kilopascal gives 101.3 kPa. This means that, on each 1 m² of surface, the force acting is 1.013 kN.

Problem 3

A mercury barometer in a physics laboratory shows a 732 mm vertical column of mercury. Calculate the atmospheric pressure in pascal. (Given density of mercury ρ = 1.36 × 10⁴ kg m⁻³ g = 9.8 m s⁻²)

Solution:

Atmospheric pressure in the laboratory, P = hρg = 732 × 10⁻³ × 1.36 × 10⁴ × 9.8 = 9.76 × 10⁴ Pa (or) 0.976 × 10⁵ Pa

3.3.2 Gauge pressure and absolute pressure

Our daily activities are happening in the atmospheric pressure. We are so used to it that we do not even realise. When tyre pressure and blood pressure are measured using instruments (gauges) they show the pressure over the atmospheric pressure. Hence, absolute pressure is zero-referenced against a perfect vacuum and gauge pressure is zero-referenced against atmospheric pressure.

For pressures higher than atmospheric pressure, absolute pressure = atmospheric pressure + gauge pressure

For pressures lower than atmospheric pressure absolute pressure = atmospheric pressure - gauge pressure

We have seen that liquid column exerts pressure. So the pressure inside the sea will be more. This is more than twice the atmospheric pressure. Parts of our body, especially blood vessels and soft tissues cannot withstand such high pressure. Hence, scuba divers always wear special suits and equipment to protect them.

Do You Know?

In petrol bunks, the tyre pressure of vehicles is measured in a unit called p.s.i. It stands for pascal per inch, an old system of unit for measuring pressure.

3.4 Pascal's Law

Pascal's principle is named after Blaise Pascal (1623 - 1662) a French mathematician and physicist. The law states that the external pressure applied on an incompressible liquid is transmitted uniformly throughout the liquid. Pascal's law can be demonstrated with the help of a glass vessel having holes all over its surface. Fill it with water. Push the piston. The water rushes out of the holes in the vessel with the same pressure. The force applied on the piston exerts pressure on water. This pressure is transmitted equally throughout the liquid in all directions. This principle is applied in various machines used in our daily life.

3.4.1 Hydraulic press

Pascal's law became the basis for one of the important machines ever developed, the hydraulic press. It consists of two cylinders of different cross-sectional areas. They are fitted with pistons of cross-sectional areas "a" and 'A'. The object to be lifted is placed over the piston of large cross-sectional area A. The force F₁ is applied on the piston of small cross-sectional area 'a'. The pressure P produced by small piston is transmitted equally to large piston and a force F₂ acts on A which is much larger than F₁.

Pressure on piston of small area 'a' is given by, P = F₁ ÷ A₁ ... equation (1)

Applying Pascal's law, the pressure on large piston of area A will be the same as that on small piston.

Therefore, P = F₂ ÷ A₂ ... (2)

Comparing equations (1) and (2) we get F₁ ÷ A₁ = F₂ ÷ A₂

or F₂ = F₁ × A₂ ÷ A₁

Since, the ratio A₂ ÷ A₁ is greater than 1, the force F₂ that acts on the larger piston is greater than the force F₁ acting on the smaller piston. Hydraulic systems working in this way are known as force multipliers.

Problem 4

A hydraulic system is used to lift a 2000 kg vehicle in an auto garage. If the vehicle sits on a piston of area 0.5 m², and a force is applied to a piston of area 0.03 m², what is the minimum force that must be applied to lift the vehicle?

Given: Area covered by the vehicle on the piston A₁ = 0.5 m², Weight of the vehicle, F₁ = 2000 kg × 9.8 m s⁻², Area on which force F₂ is applied, A₂ = 0.03 m²

Solution:

P₁ = P₂; F₁ ÷ A₁ = F₂ ÷ A₂ and F₂ = F₁ ÷ A₁ × A₂

F₂ = (2000 × 9.8) × 0.03 ÷ 0.5 = 1176 N

3.5 Density

Activity 5

Take two identical flasks and fill one flask with water to 250 cubic centimeter mark and the other with kerosene to the same 250 cubic cm mark. Measure them in a balance. The flask filled with water will be heavier than the one filled with kerosene. Why? The answer is in finding the mass per unit volume of kerosene and water in respective flasks.

To understand density better, let us assume that the mass of the flask be 80 g. So, the mass of the flask filled with water is 330 g and the mass of flask filled with kerosene is 280 g. Mass of water only is 250 g and kerosene only is 200 g.

Mass per unit volume of water is 250 ÷ 250 cubic cm. This is 1 g per cubic cm.

Mass per unit volume of kerosene is 200 g ÷ 250 cubic cm. This is 0.8 g per cubic cm.

The result 1 g per cubic cm and 0.8 g cubic cm are the densities of water and kerosene respectively. Therefore, the density of a substance is the mass per unit volume of a given substance. The SI unit of density is kilogram per meter cubic (kg per cubic m) also gram per cubic centimeter (g per cubic cm). The symbol for density is ρ.

3.5.1 Relative Density

We can compare the densities of two substances by finding their masses. But, generally density of a substance is compared with the density of water at 4°C because density of water at that temperature is 1 g per cubic cm. Density of any other substance with respect to the density of water at 4°C is called the relative density.

Relative Density Formula

Relative density (R.D.) = density of the substance ÷ density of water at 4°C

We know that, Density = mass ÷ volume

Therefore Relative density = (mass of the substance ÷ volume of the substance) ÷ (mass of water ÷ volume of water)

Since the volume of the substance is equal to the volume of water,

Relative density = mass of certain volume of the substance ÷ mass of equal volume of water at 4°C

3.5.2 Measurement of relative density

Relative density can be measured using Pycnometer also called density bottle. It consists of ground glass stopper with a fine hole through it. The function of the hole in a stopper is that, when the bottle is filled and the stopper is inserted, the excess liquid rises through the hole and runs down outside the bottle. By this way the bottle will always contain the same volume of whatever the liquid is filled in, provided the temperature remains constant. Thus, the density of a given volume of a substance to the density of equal volume of referenced substance is called relative density or specific gravity of the given substance. If the referenced substance is water then the term specific gravity is used.

3.5.3 Floating and sinking

Whether an object will sink or float in a liquid is determined by the density of the object compared to the density of the liquid. If the density of a substance is less than the density of the liquid it will float. For example a piece of wood which is less dense than water will float on it. Any substance having more density than water (for example, a stone), will sink into it.

Problem 5

You have a block of a mystery material, 12 cm long, 11 cm wide and 3.5 cm thick. Its mass is 1155 grams. (a) What is its density? (b) Will it float in a tank of water, or sink?

Solution:

(a) Density = mass ÷ volume = 1155 g ÷ (12 cm × 11 cm × 3.5 cm) = 1155 g ÷ 462 cubic cm = 2.5 g cm⁻³

(b) The mystery material is denser than the water. So it sinks.

3.5.4 Application of principle of flotation

Hydrometer

A direct-reading instrument used for measuring the density or relative density of the liquid is called hydrometer. Hydrometer is based on the principle of flotation, That is the weight of the liquid displaced by the immersed portion of the hydrometer is equal to the weight of the hydrometer. Hydrometer consists of a cylindrical stem having a spherical bulb at its lower end and a narrow tube at its upper end. The lower spherical bulb is partially filled with lead shots or mercury. This helps hydrometer to float or stand vertically in liquids. The narrow tube has markings so that relative density of a liquid can be read directly. The liquid to be tested is poured into the glass jar. The hydrometer is gently lowered in to the liquid until it floats freely. The reading against the level of liquid touching the tube gives the relative density of the liquid.

Hydrometers may be calibrated for different uses such as lactometers for measuring the density (creaminess) of milk, saccharometer for measuring the density of sugar in a liquid and alcoholometer for measuring higher levels of alcohol in spirits.

Lactometer

One form of hydrometer is a lactometer, an instrument used to check the purity of milk. The lactometer works on the principle of gravity of milk. The lactometer consists of a long graduated test tube with a cylindrical bulb with the graduation ranging from 15 at the top to 45 at the bottom. The test tube is filled with air. This air chamber causes the instrument to float. The spherical bulb is filled with mercury to cause the lactometer to sink up to the proper level and to float in an upright position in the milk. Inside the lactometer there may be a thermometer extending from the bulb up into the upper part of the test tube where the scale is located. The correct lactometer reading is obtained only at the temperature of 60 °F. A lactometer measures the cream content of milk. More the cream, lower the lactometer floats in the milk. The average reading of normal milk is 32. Lactometers are used at milk processing units and dairies.

3.6 Buoyancy

We already saw that a body experiences an upward force due to the fluid surrounding, when it is partially or fully immersed in to it. We also know that pressure is more at the bottom and less at the top of the liquid. This pressure difference causes a force on the object and pushes it upward. This force is called buoyant force and the phenomenon is called buoyancy.

Most buoyant objects are those with a relatively high volume and low density. If the object weighs less than the amount of water it has displaced (density is less), buoyant force will be more and it will float (such object is known as positively buoyant). But if the object weighs more than the amount of water it has displaced (density is more), buoyant force is less and the object will sink (such object is known as negatively buoyant).

Do You Know?

Salt water provides more buoyant force than fresh water, because, buoyant force depends as much on the density of fluids as on the volume displaced.

3.6.1 Cartesian diver

Cartesian diver is an experiment that demonstrates the principle of buoyancy. It is a pen cap with clay. The Cartesian diver contains just enough liquid that it barely floats in a bath of the liquid; its remaining volume is filled with air. When pressing the bath, the additional water enters the diver, thus increasing the average density of the diver, and thus it sinks.

3.7 Archimedes' Principle

Archimedes principle is the consequence of Pascal's law. According to legend, Archimedes devised the principle of the 'hydrostatic balance' after he noticed his own apparent loss in weight while sitting in his bath. The story goes that he was so enthused with his discovery that he jumped out of his bath and ran through the town, shouting 'eureka'.

Archimedes' Principle

Archimedes principle states that 'a body immersed in a fluid experiences a vertical upward buoyant force equal to the weight of the fluid it displaces'

When a body is partially or completely immersed in a fluid at rest, it experiences an upthrust which is equal to the weight of the fluid displaced by it. Due to the upthrust acting on the body, it apparently loses a part of its weight and the apparent loss of weight is equal to the upthrust.

Thus, for a body either partially or completely immersed in a fluid,

Upthrust = Weight of the fluid displaced = Apparent loss of weight of the body

Apparent weight of an object = True weight of an object in air - Up thrust (weight of water displaced)

3.8 Laws of flotation

Laws of flotation are

1. The weight of a floating body in a fluid is equal to the weight of the fluid displaced by the body.
2. The centre of gravity of the floating body and the centre of buoyancy are in the same vertical line.

The point through which the force of buoyancy is supposed to act is known as centre of buoyancy.

Do You Know?

Flotation therapy uses water that contains Epsom salts rich in magnesium. As a floater relaxes, he or she is absorbing this magnesium through the skin. Magnesium helps the body to process insulin, which lowers a person's risk of developing Type 2 Diabetes.

Points to Remember

• The force which produces compression is called thrust. Its S.I. unit is newton.
• Thrust acting normally to a unit area of a surface is called pressure. Its S.I. unit is pascal.
• The pressure exerted by the atmospheric gases on its surroundings and on the surface of the earth is called atmospheric pressure.
• 1 atm is the pressure exerted by a vertical column of mercury of 76 cm height.
• Barometer is an instrument used to measure atmospheric pressure.
• The upward force experienced by a body when partly or fully immersed in a fluid is called upthrust or buoyant force.
• Cartesian diver is an experiment which demonstrates the principle of buoyancy and the ideal gas law.
• Pascal's law states that an increase in pressure at any point inside a liquid at rest is transmitted equally and without any change, in all directions to every other point in the liquid.
• Archimedes' principle states that when a body is partially or wholly immersed in a fluid, it experiences an up thrust or apparent lose of weight, which is equal to the weight of the fluid displaced by the immersed part of the body.
• Density is known as mass per unit volume of a body. Its S.I. unit is kg m⁻³
• Relative density is the ratio between the density of a substance and density of water.
• Relative density of a body is a pure number and has no unit.
• Hydrometer is a device used to measure the relative density of liquids based on the Archimedes' principle.
• Lactometer is a device used to check the purity of milk by measuring its density using Archimedes' principle.

Glossary

Altitude Vertical distance in the up direction. Astronaut Person who is specially trained to travel into outer space. Axes Simple machine to cut, shape and split wood. Deformation Changes in an object's shape or form due to the application of a force or forces. Iceberg Large piece of ice floating in water. Hydraulic systems Device that uses fluids and work under the fluid pressure to control valves. Incompressible No change in volume if a pressure is applied. Meteorological Weather condition. Piston Movable disc fitted inside a cylinder. Propellers Fan that transmits power in the form of thrust by rotation. Syringe Simple pump made of plastic or glass to inject or withdraw fluid. Therapy Treatment given for healing sickness. Velocity Speed of objects with direction.

TEXTBOOK EXERCISES

Exercise 1. Choose the correct answer

1. The size of an air bubble rising up in water

a. decreases b. increases c. remains same d. may increase or decrease

2. Clouds float in atmosphere because of their low

a. density b. pressure c. velocity d. mass

3. In a pressure cooker, the food is cooked faster because

a. pressure lowers the boiling point. b. increased pressure raises the boiling point. c. decreased pressure raises the boiling point. d. increased pressure lowers the melting point.

4. An empty plastic bottle closed with an airtight stopper is pushed down into a bucket filled with water. As the bottle is pushed down, there is an increasing force on the bottom. This is because,

a. more volume of liquid is displaced. b. more weight of liquid is displaced. c. pressure increases with depth. d. All the above. Exercise 2. Fill in the blanks

1. The weight of the body immersed in a liquid appears to be than its actual weight.

2. The instrument used to measure atmospheric pressure is

3. The magnitude of buoyant force acting on an object immersed in a liquid depends on of the liquid.

4. A drinking straw works on the existence of

Exercise 3. State whether true or false. If false, correct the statement 1. The weight of fluid displaced determines the buoyant force on an object. 2. The shape of an object helps to determine whether the object will float or not. 3. The foundations of high-rise buildings are kept wide so that they may exert more pressure on the ground. 4. Archimedes' principle can also be applied to gases. 5. Hydraulic press is used in the extraction of oil from oil seeds. Exercise 4. Match the following

Density
h ρ g
Pascal's law
Milk
Pressure exerted by a fluid
mass per volume
Lactometer
Pressure

Exercise 5. Answer in brief

1. On what factors the pressure exerted by the liquid depends on?

2. Why does a helium balloon float in air?

3. Why it is easy to swim in sea water than in river water?

4. What is meant by atmospheric pressure?

5. State Pascal's law?

Exercise 6. Answer in detail

1. With an appropriate illustration prove that the force acting on a smaller area exerts a greater pressure.

2. Describe the construction and working of mercury barometer.

3. How does an object's density determine whether the object will sink or float in water?

4. Explain the construction and working of a hydrometer with diagram.

5. State the laws of flotation.

Exercise 7. Assertion and reason type questions

Mark the correct answer as:

(a) If both assertion and reason are true and reason is the correct explanation of assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of assertion.

(c) If assertion is true but reason is false.

(d) If assertion is false but reason is true.

1. Assertion: To float, body must displace liquid whose weight is equal to the actual weight.

Reason: The body will experience no net downward force in that case.

a b c d

2. Assertion: Pascal's law is the working principle of a hydraulic lift.

Reason: Pressure is thrust per unit area.

a b c d Exercise 8. Numerical Problems

1. A block of wood of weight 200 g floats on the surface of water. If the volume of block is 300 cubic cm, calculate the upthrust due to water.

2. Density of mercury is 13600 kg m⁻³. Calculate the relative density.

3. The density of water is 1 g cm⁻³. What is its density in S.I. units?

4. Calculate the apparent weight of wood floating on water if it weighs 100 g in air.

Exercise 9. Higher Order Thinking Skills

1. How high does the mercury level in barometer stand on a day when atmospheric pressure is 98.6 kPa?

2. How does a fish manage to rise up and move down in water?

3. If you put one ice cube in a glass of water and another in a glass of alcohol, what would you observe? Explain your observations.

4. Why does a boat with a hole in the bottom would eventually sink?

Reference Books

1. Fundamentals of Physics - By David Halliday and Robert Resnick.
2. I C S E Concise Physics - By Selina publisher.
3. Physics - By Tower, Smith Tuston and Cope.

Internet Resources

https://www.teachengineering.org/lessons/view/cub_airplanes_lesson04

http://www.cyberphysics.co.uk/topics/earth/atmosphr/atmospheric_pressure.htm

http://discovermagazine.com/2003/mar/featscienceof

http://northwestfloatcenter.com/how-flotationcan-help-your-heart/

ICT CORNER

Fluid Experiment with fluid Pressure and Flow using virtual simulator

Steps

1. Type the given URL to reach "pHET Simulation" page and download the "java" file of"Fluid Pressure and Flow".
2. Open the "java" file.
3. Open the water tap and observe the "Pressure" fluctuations by increasing"Fluid density" and "Gravity".
4. Select the third picture and drop down a weight scales to transform weight into pressure.
5. Switch to "Flow" tab from the top to simulate fluid motion under a given shape and pressure.
6. Click the "red" button to drop dots into the fluid and alter the pipe shape by dragging the yellow holders.

Fluid Pressure and Flow Simulator URL: https://phet.colorado.edu/en/simulation/fluid-pressure-and-flow or Scan the QR Code.

📝 Summary

1. Pressure is defined as thrust per unit area (Pressure = thrust/area of contact), measured in pascals (Pa) where 1 Pa = 1 N m⁻²
2. For the same given force, if the area is large pressure is low and vice versa - this explains why sharp objects penetrate easily and why camels can run on sand
3. Thrust is the force acting perpendicular to a surface, and its effect depends on the area on which it acts
4. The unit of thrust is newton (N) and the unit of pressure is newton per square metre (N m⁻²), named pascal after French scientist Blaise Pascal
5. Fluids behave differently from solids when pressure increases - while solids deform or break, fluids flow rather than deform