Category: Science

Chapter 14: “Natural resources”

KEY CONCEPTS : [ *rating as per the significance of concept]

CONCEPTS	RATING
Breath of air	**
A wonder liquid	***
Biogeochemical cycles	*****

1. The” Biosphere” is the life supporting zone of the earthwith three sub-zones called as lithosphere (rock part), atmosphere (air part)and hydrosphere (water part).

Breath of air

1. Composition of Air

1. The interactions between different components of the Biosphere to maintain the balance between the biotic and a biotic component makes “Biogeochemical cycle”. Ex. Water Cycle, Nitrogen Cycle, Carbon cycle, Oxygen Cycle,
2. Role of atmosphere in climate control : atmosphere act as protective blanket for the earth. Since atmosphere is a bad conductor of heat, it keeps the average temperature of the earth constant. At night, it slows down the escape of heat into outer space.
3. The movement of air : the atmosphere gets heated from the radiation that is reflected back by the land or water bodies. As a result of heating, convection currents are set up in the air. Since land gets heated faster than water, the air over land gets heated faster than air above water bodies.
4. In coastal regions, during the day, the air above the land gets heated faster and starts rising. So a region of low pressure is created and air over sea moves into this area of low pressure. The movement of air from one region to the other region causes Wind.
5. During the day, the direction of wind would be from the sea to the land and at night, both land and sea starts to cool. Since water cools down slower than the land, the air above water would be warmer than air above land, thus the direction of wind would be from the land to the sea.
6. Air pollution : it is an undesirable change in the physical, chemical or biological characteristics. It is caused due to an increase in the content of harmful substances (pollutant) such as oxides of nitrogen and sulphur, etc.
7. 
   Harmful effect of air pollution :

• It affects the respiratory system causing breathing difficulties eg; bronchitis, asthma, lung cancer, tuberculosis, etc.
• Burning of fossil fuels like coal and petroleum releases oxides of nitrogen and sulphur. Inhalation of these gases is dangerous.
• Combustion of fossil fuel also increases the amount of suspended particles in air. The presence of high levels of all these pollutants, reduce visibility in cold weather where water also condenses out of air forming smog.
• Acid rain formed from the gases like sulphur dioxide and nitrogen oxides present in polluted air. It causes damage to living and non- living thing.

1. 
   The Water Cycle:
2. The process in which water evaporates and falls on the land as rain and later flows back into the sea via rivers is known as the “Water Cycle”. Water flows through rocks containing soluble minerals, some of them get dissolved in the water. Thus the rivers carry many nutrients from the land to sea and these are used by the marine organisms.
3. When the water vapors condense as water droplets and grow big and heavy, they fall down in the form of “rain”. It ranges from 5 cm to 200 cm of rain fall in a year in our country. In large parts of India, rains are mostly brought by the south-west or north-east monsoons. Depressions in the Bay of Bengal may also cause rains in some areas.
4. Water is a wonder liquid because all cellular processes take place in a water medium; substances are transported in a dissolved form; terrestrial forms require fresh water to maintain the equilibrium of salts; major resource to determine the life on the earth.
5. The dissolved fertilizers (NPK fertilizers), pesticides (DDT), sewage (Disease causing Organisms), waste from factories (Mercury) and water released from the dams can affect the life forms on the earth. The dissolved Oxygen is being used by the animals and plants that live in water, would adversely affect the aquatic organisms. The change in temperature would be dangerous for the eggs and larvae of the various animals particularly susceptible to temperature changes. It leads to “water pollution”.

(Please refer Fig. 14.5, NCERT Text Book Page-197).

1. Nitrogen Cycle:
2. The nitrogen gas makes up 78% of our atmosphere. It is essential for the synthesis of proteins, DNA, RNA, urea, alkaloids and Vitamins.
3. The simple molecular nitrogen from the atmosphere is converted into more complex molecules in the living beings and back again to atmosphere is called “Nitrogen Cycle”.
4. Nitrogen fixation by Lightening: During lightning, the molecular nitrogen is converted into oxides of nitrogen and dissolves in water to give nitric and nitrous acids and fall on lands along with rains. These are then utilized by various life forms.
5. Nitrogen fixation by Bacteria: The molecular nitrogen is converted into nitrates and nitrites, by free living bacteria or the bacteria present in the root nodules of legumes.
6. The conversion of molecular nitrogen into nitrates and nitrites is called as” Nitrification”. Plants generally covert them into amino acids. The conversion of nitrates and nitrates into Ammonia is called as” Ammonification”. The conversion of Ammonia into molecular Nitrogen is called as” Denitrification”. Thereby nitrates and nitrites are converted into molecular or elemental nitrogen in the nature. (Please refer Fig. 14.6, NCERT Text Book Page- 198).
7. The Carbon cycle:
8. The Carbon dioxide gas makes up 0.039 % of our atmosphere. Carbon occurs in the elemental form as diamonds and graphite in earth. Carbon is essential for the synthesis of proteins, carbohydrates, fats, nucleic acids and Vitamins in living organisms.
9. The Carbon dioxide Fixation: Green plants convert Carbon dioxide into glucose in the presence of sunlight through Photosynthesis. The glucose molecules are converted into other biologically important molecules. And many marine animals use carbonates dissolved in sea water to make shells, exoskeletons.
10. The combustion: The Carbon dioxide in the atmosphere is added by the process of combustion, where fuels are burnt to provide energy for various needs like heating, cooking, transportation, and industrial process.
11. The Greenhouse Effect: The percentage of Carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings stated burning fossil fuels on a very large scale. The Carbon dioxide is a greenhouse gas. The increase in the Carbon dioxide content would cause more heat to be retained by the atmosphere and lead to Global Warming. It is called” Greenhouse Effect”
12. The carbon cycle is repeated through different physical and biological activities. (Please refer Fig. 14.7, NCERT Text Book Page- 199).

6 .Oxygen Cycle:

1. The Oxygen gas makes up 21 % of our atmosphere. Oxygen is essential component of proteins, carbohydrates, fats, nucleic acids in living organisms.
2. Oxygen from our atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen. Oxygen is returned to the atmosphere in only one major process, that is, Photosynthesis, it is called as Oxygen Cycle.
3. The air is heated faster than water; the air over land would also be heated faster than the air over water bodies. The movement of air from one region to the other creates winds, during the day the direction of the wind would be from the sea to land. At night, both land and sea start to cool.
4. The oxides of nitrogen and sulphur gases dissolve in rain to gives rise to “Acid rains”. The smog is a visible indication of Air Pollution. The pollutants bring respiratory, cardiac problems and allergies. The organisms called Lichens are found on the bark of trees, they are indicators of pollution free environment. Three atoms of Oxygen ( O₃) is called as Ozone. The Ozone is poisonous but absorbs harmful radiations from the Sun. The Ozone layer around the earth, if, dwindles further may cause Health hazards including Cancers . Recently discovered the Ozone hole; in the region of Antarctica. (Please refer Fig. 14.8 & 14.9, NCERT Text Book Page- 200).

QUESTION BANK

1. What are the three sub-zones in the Biosphere? {Lithosphere (rock part), atmosphere (air part)and hydrosphere (water part)}.
2. The process in which water evaporates and falls on the land as rain and later flows

back into the sea via rivers is known (Water Cycle).

1. In large parts of India, rains are mostly brought by monsoons.( the south

west or north-east monsoons).

1. Why water is a wonder liquid? Justify ( A major resource to determine life on the earth)
2. What are the four major water Pollutants?{ (NPK fertilizers, pesticides (DDT), sewage (Disease causing Organisms), waste from factories (Mercury)}
3. Write a short notes on Nitrogen fixation by Bacteria.{The molecular nitrogen is converted into nitrates and nitrites, by free living bacteria or the bacteria present in the root nodules of legumes}.
4. What is Greenhouse Effect? {The Carbon dioxide is a greenhouse gas. The increase in the Carbon dioxide content would cause more heat to be retained by the atmosphere and lead to Global Warming. It is called” Greenhouse Effect”}
5. What is the percentage of Oxygen gas in our atmosphere? {21 %}
6. Which organisms are found on the bark of trees as indicators of pollution free environment? { Lichens}
7. Write about the Ozone hole in the Antarctica. {The Ozone layer around the earth is dwindling further to damage and cause Health hazards including Cancers. Recently discovered Ozone hole in the Antarctica.}

QUESTION PAPER:FORMATIVE ASSESSMENT – I (For Practice)

Marks- 40 Time: 90 minutes

• General Instructions

1. Questions 1-5 (1 Mark each) 2. Questions 6-10 ( 2 Mark each)

1. Questions 11-15 (3Mark each) 4. . Questions 16-17 (5Mark each)

Q.1 What is called Lithosphere, define it.

Q.2 Water covers 75% of the Earth’s surface. Mention True/ false

Q.3 What is the percentage of Carbon dioxide on Venus

Q.4 What is the range of temperature on the Moon

Q.5 Define the term Pollutant

Q.6 What are the two ways to fix Carbon dioxide on earth.

Q.7 Mention any two important features of Water.

Q.8 How the Depressions effect our environment?

Q.9 Define the term Soil Pollution. Give one reason for it.

Q.10 How changes of temperature effect living organisms in water?

Q.11 What is Humus? Mention its importance in two points.

Q12 What is deforestation? Give two reasons for it.

Q.13. Define Global Warming, mention two causes for it.

Q.14 What is Ozone Depletion? Give two reasons for it.

Q.15 Draw the schematic diagram of Water Cycle in the nature.

Q.16. Write any five salient features of Nitrogen Cycle with a suitable diagram.

Q.17 Write about Industrial Pollution and mention five effects in the environment.

CHAPTER 12 – “Sound”

KEY CONCEPTS [ *rating as per the significance of concept]

1	Production of Sound	****
2	Propagation of Sound	*****
3	Reflection of Sound	*****
4	Echo	****
5	Uses Of Multiple Reflection Of Sound	***
6	Range of Hearing	***
7	Applications of Ultrasound	**
8	SONAR	**
9	Structure of Human Ear	****

1. 
   Production of Sound

Sound is produced due to the vibration of objects. Vibration is the rapid to and fro motion of an object.

Vibrating objects are the source of all sounds Irregular, chaotic vibrations produce noise Regular, controlled vibration can produce music All sound is a combination of pure frequencies A stretched rubber band when plucked vibrates and produces sound.

1. 
   Propagation of Sound

When an object vibrates, the particles around the medium vibrate. The particle in contact with the vibrating object is first displaced from its equilibrium position

The disturbance produced by the vibrating body travels through the medium but the particles do not move forward themselves.

A wave is a disturbance which moves through a medium by the vibration of the particles of the medium. So sound is considered as a wave.Sound waves Require medium for transmission.Sound waves are called mechanical waves. When a vibrating object moves forward, it pushes and compresses the air in front of it forming a region of high pressure called compression (C). When the vibrating object moves backward, it forms a region of low pressure called rarefaction (R).

Sound is longitudinal wave motion

A vibrating object producing a series of compressions (C) and rarefaction (R)

In these waves the particles move back and forth parallel to the direction of propagation of the disturbance. Such waves are called longitudinal waves.

There is another kind of waves called transverse waves. In these waves the particles oscillate up and down perpendicular to the propagation of the direction of disturbance.

Sound propagates in a medium as a series of compressions (C) and rarefactions (R).

Compressions are the regions of high pressure and density where the particles are crowded and are represented by the upper portion of the curve called crest.

Rarefactions are the regions of low pressure and density where the particles are spread out and are represented by the lower portion of the curve called trough Characteristics of a sound wave

Frequency of sound wave

The number of oscillations per unit time is called the frequency of the sound wave. It is represented by the symbol V (Greek letter nu). Its SI unit is hertz (Hz)

Time period of sound wave

Frequency and time are represented as follows:- V for one oscillation 1 1

T = — or V = —

V T

Amplitude of sound wave

The amplitude of sound wave is the height of the crest or tough. It is represented by the letter A.

The SI unit is the same as that of density or pressure.

Wavelength and Amplitude

The wavelength is the distance between the “crests” of two waves that are next to each other. The amplitude is how high the crests are.

Pitch and loudness of sound

The pitch of sound (shrillness or flatness) depends on the frequency of vibration.

If the frequency is high, the sound has high pitch and if the frequency is low, the sound has low pitch Speed of sound

The speed of sound is more in solids, less in liquids and least in gases.

The speed of sound also depends on the temperature of the medium. If the temperature of the medium is more, the speed of sound is more

1. 
   Reflection of Sound

Sound gets reflected at the surface of a solid or liquid and follows the laws of reflection.

1. The angle of incidence is equal to the angle of reflection.
2. The incident ray, the reflected ray and normal at the point of incidence all lie in the same plane.

Plate

o

► Screen

Renection of sound from a plane surface

4. Echo

If we shout or clap near a reflecting surface like tall building or a mountain, we hear the same sound again. This sound which we hear is called echo. It is caused due to the reflection of sound.

To hear an echo clearly, the time interval between the original sound and the echo must be at least 0.1 s.

Since the speed of sound in air is 344 m/s, the distance travelled by sound in 0.I s = 344 m/s x 0.1 s = 34.4 m

So to hear an echo clearly, the minimum distance of the reflecting surface should be half this distance that is 17.2 m.

Reverberation

Echoes may be heard more than once due to repeated or multiple reflections of sound from several reflecting surfaces. This causes persistence of sound called reverberation.

In big halls or auditoriums to reduce reverberation, the roofs and walls are covered by sound absorbing materials like compressed fibre boards, rough plaster or draperies.

1. 
   Uses Of Multiple Reflection Of Sound

Megaphones, horns, musical instruments like trumpets, etc. are deigned to send sound by multiple reflection in a particular direction without spreading in all directions.

1. Doctors listen to sounds from the human body through a stethoscope. The sound of heartbeat reaches the doctor’s ears by multiple reflection.
2. Generally the ceilings of cinema halls and auditoriums are curved so that sound after multiple reflection reaches all parts of the hall.

Sometimes a curved sound board is placed behind the stage so that sound after multiple reflection spreads evenly across the hall.

1. 
   Range of Hearing

Human beings can hear sound frequencies between 20 Hz and 2000 Hz.

Sound whose frequency is less than 20 Hz is called infrasonic sound Sound whose frequency is more than 2000 Hz is called ultrasonic sound

1. _Uses of ultrasonic sound

Ultrasonic sound is used to clean objects like electronic Components, used to detect cracks in metal blocks, used in ultra sound scanners for getting images of internal organs of the human body used to break small stones formed in the kidneys into fine grains.

8 Sonar

It is a device which uses ultrasonic waves to measure distance, direction and speed of underwater objects. The distance of the object can be calculated by knowing the speed of sound in water and the time taken between the transmission and reception of ultrasound

The sound waves passes through the ear canal to a thin membrane called eardrum. The eardrum vibrates. The vibrations are amplified by the three bones of the middle ear called

hammer, anvil and stirrup. Middle ear then transmits the sound waves to the inner ear. The brain then interprets the signals as sound.

QUESTION BANK

One mark questions

1. What do you understand by sound waves?
2. Give an example to show that sound travels at a finite speed.
3. Is sound wave longitudinal or transfer.
4. Name two quantities that vary periodically at a place in air as a sound wave travels through it .
5. An airplane produces a sound wave with frequency of 5 KHz and wavelength 30 m. In how much time would the sound wave cover the distance of 4 Km?
6. With the help of a diagram show how longitudinal waves like sound waves travel in air.
7. With the help of a diagram show how longitudinal waves like sound waves travel in air.
8. Can we hear the ringing of a mobile phone placed in a vacuum chamber?
9. Can two astronauts talk on moon a they does on the surface of the earth?

Two marks questions

1. Explain how echoes are used by bats to judge the distance of an obstacle?
2. State the special properties of ultrasound that make it useful to us .In general, how these properties are utilized.
3. Why is soft furnishing avoided in concert halls?
4. Draw a diagram depicting low pitched sound and high pitched sound and write main difference between the two?
5. Distinguish between longitudinal and transverse waves. Give one example each.
6. An explosion takes place at the moon. After what time would it be heard at the earth?

Three marks questions

1. Two sources A and B vibrate with the same amplitude. They produce sounds of frequencies 1 kHz and 30 kHz respectively. Which of the two waves will have greater power?
2. Find the time period of the source of a sound wave whose frequency is 400Hz.
3. A sound wave travels at a speed of 340m/s. If its wavelength is 2 cm, what is the frequency of the wave? Will it be in the audible range?
4. The grandparents and parents of a two year girl are playing with her in a room. A sound source produces a 28—kHzsound.who in the room is most likely to hear the sound?

Five marks questions

1. Sound cannot travel in vacuum. Describe an experiment to demonstrate this.
2. With the help of a diagram describe how compression and rarefaction pulses are produced in air near a source of sound.
3. Explain briefly how a flaw in a mental component can be detected using ultrasound?
4. Explain the working and application of SONAR.
5. A monkey drops a coconut from the top of a tree. He hears the sound of the coconut hitting the ground 2.057 seconds after dropping it .If the monkey was 19.6 metres above the ground, what is the speed of sound in air?(take g = 9.8m/s²).
6. Draw a neat diagram of human ear. Explain the function of various parts. What have you learnt

Longitudinal waves: Those in which the direction of vibration is the same as their direction of propagation. So the movement of the particles of the medium is either in the same or in the opposite direction to the motion of the wave. Exemple: sound waves, what changes in this case is the pressure of the medium (air, water or whatever it be).

Transverse waves: The oscillations occur perpendicularly to the direction of energy transfer. Exemple: a wave in a tense string. Here the varying magnitude is the distance from the equilibrium horizontal position

A general property of waves is that their speed relative to medium depends on the properties of medium but is independent of the motion of the source of waves. If the observer is in motion with respect to the medium, the velocity of wave propagation relative to the observer wil be different. A remarkable exception is encountered in the case of light PROPERTIES Frequency

• Wavelength
• Period
• Amplitude
• Intensity
• Speed
• Direction Perception of Sound

For humans, hearing is limited to frequencies between about 20 Hz and 20000 Hz, with the upper limit generally decreasing with age.

KEY LEARNING:

Vibration – repetitive back and forth motion Periodic motion – a motion that repeats itself Mechanical waves require medium for propagation Waves move through medium but medium remains in place

Longitudinal waves-Vibration direction parallel to wave propagation direction Particles in medium move closer together/farther apart .Example: sound waves Gases and liquids – support only longitudinal waves Transverse waves-

Vibration direction perpendicular to wave propagation direction .Example: plucked string Solids – support both longitudinal and transverse waves Sound waves Require medium for transmission

1. Sound is a wave motion, produced by a vibrating source.
2. A medium is necessary for the propagation of sound waves.
3. Sound is a longitudinal wave in which the particles of medium move along the direction of motion of wave.
4. The part or region of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is known as compression.
5. The part or region of a longitudinal wave in which the density of the particles of the medium is lesser than the normal density is called a rarefaction.
6. The point of maximum positive displacement on a transverse wave is known as crest.
7. The point of maximum negative displacement on a transverse wave is known as through.
8. A wave or short duration which is confined to a small portion of a medium at any given time is known as a pulse.
9. The maximum displacement of particles of the medium from their mean positions during the propagation of a wave is known as amplitude of the wave.
10. The distance traveled by a wave in one second is called wave velocity. It depends upon the nature of the medium through which it passes.
11. The speed of sound depends primarily on the nature and the temperature of the transmitting medium.
12. Sound travels faster in solids than in air. The speed of sound in solids is much more than the speed of sound in liquids or gases.
13. The distance between two consecutive compressions or two consecutive rarefactions is called the wavelength.
14. Frequency is defined as the number of oscillations per second.
15. The time taken by the wave for one complete oscillation of the density or pressure of the medium is called the time period, T.
16. How the brain interprets the frequency of an emitted sound is called the pitch of sound.
17. Loudness is the degree of sensation of sound produced.
18. Sound properties such as pitch, loudness and quality are determined by the corresponding wave properties.
19. Sound gets reflected and follows the same law as the reflection of light.
20. The persistence of sound due to repeated reflection and its gradual fading away is called reverberation of sound.
21. Echo is a repetition of sound due to the reflection of original sound by a large and hard obstacle.
22. The audible range of hearing for average human beings is in the frequency range of 20 Hz – 20 kHz.
23. The amount of sound energy passing each second through unit area is called the intensity of sound.
24. Sound of frequency less than 20 Hz is known as infrasound and greater than 20 kHz is known as ultrasound.
25. Ultrasound has many medical and industrial applications.
26. SONAR stands for Sound Navigation and Ranging and it works on the principle of reflection of sound waves.
27. The SONAR technique is used to determine the depth of the sea and to locate under water hills, valleys, submarines, icebergs sunken ships etc.

CHAPTER 11 “Work & Energy”

KEY CONCEPTS [ *rating as per the significance of concept]

1	Work Done By A Constant Force	***
2	Energy And Its Forms(Kinetic Energy & Potential Energy) Are Various Energy Forms Inter convertible?
3	Potential Energy Of An Object At A Height	*****
4	Law Of Conservation Of Energy	****
5	Rate Of Doing Work & Commercial Unit Of Energy	****

1. Work Done By A Constant Force

• Work is a scalar quantity equal to the product of the displacement x and the

component of the force F_x in the direction of the displacement..

• Work is defined as a force acting upon an object to cause a displacement
• Mathematically, work can be expressed by the following equation.
• W= F x d cos q ( cos 0⁰ = 1)
• where F = force, d = displacement, and the angle (theta) is defined as the angle between the force and the displacement vector
• Three things are necessary for the performance of work:
• There must be an applied force F.
• There must be a displacement x.
• The force must have a component along the displacement

Negative Work

Force F contributes to displacement x.

Test Yourself:

1. Calculate Work when F= 40 N and x = 4 m.
2. Calculate Work when F = -10 N and x = 4 m.
3. A lawn mower is pushed a horizontal distance of 20 m by a force of 200 N directed at an angle of 30⁰ with the ground. What is the work of this force?
4. A student lifts a 50 pound (lb) ball 4 feet (ft) in 5 seconds (s). How many joules of work has the student completed?

2.Energy And Its Forms

James Joule

The metric system unit of energy is the joule (J), after James Joule.

• Mechanical energy is the energy which is possessed by an object due to its motion or its stored energy of position

Forms of Energy

• Kinetic energy : is the energy of motion

Energy which a body possesses because of its motion, which occurs anywhere from an atomic level to that of a whole organism

Examples of Kinetic Energy: This is not an all-inclusive list.

• Electrical – The movement of atoms
• Electromagnetic or Radiant – The movement of waves
• Thermal or Heat – The movement of molecules
• Motion – The movement of objects
• Sound – The movement through waves

Engineers generally refer to thermal/heat energy as “internal energy” and use “kinetic energy” strictly in reference to motion.

Potential Energy (Stored energy or gravitational energy)

• The capacity to do work by virtue of position or configuration
• an object can store energy as the result of its position or elastic source
• Potential Energy is maximum at the maximum HEIGHT

Energy transformation involves the conversion of one form of energy into another form. Examples of energy transformation include:

• Chemical – Food is consumed and converted into motion for playing sports or taking a test.
• Radiant – Sunlight is consumed by plants and converted into energy for growth.
• Electrical – Energy transferred to an oven is converted to thermal energy for heating our food.

Now you know the basic forms of energy. The next question is “What are the energy sources?”

There are renewable and nonrenewable sources of energy. A renewable energy source is a form of energy that is constantly and rapidly replenished by natural processes. Examples of renewable energy sources include:

• Biomass – The use of a living or once living organism as fuel
• Hydropower – The energy produced from the movement of water
• Geothermal – The use of heat from within the Earth or from the atmosphere

near oceans to warm houses or other buildings

• Wind – The use of wind to generate electricity

Solar – The use of the sun as a source of heat; for instance, to heat a room within a house, etc.

Energy Conversion Examples

Fossil fuels Chemical -> Heat -> Mechanical -> Electrical Solar cells Sunlight -> Electrical Wind turbines Kinetic ^ Mechanical -> Electrical Hydroelectric Gravitational potential -> Mechanical -> Electrical Nuclear Nuclear -> Heat -> Mechanical -> Electrical Vehicle System Conversion

Test Yourself

1. How much potential energy is lost by a 5Kg object to kinetic energy due a decrease in height of 4.5 m.
2. Potential energy of an object at a height

An object increases its energy when raised through a height.

The potential energy of an object at a height depends on the ground level or the zero level

1. Law Of Conservation Of Energy

The principle of Conservation of Mechanical Energy

The total mechanical energy (E=KE+PE) of an object remains constant as the object moves, provided that the net work done by external non-conservative forces is zero, W_nc=0J Total mechanical energy: the sum of kinetic energy and gravitational potential energy E = KE + PE

Wnc = (KEf – KE0) + (PEf – PE0)

Wnc = (KEf + PEf) – (KE0 + PE0)

Wnc = Ef – E0

Ef = KEf + PEf) E0 = KE0 + PE0

1. Rate of Doing Work & Commercial Unit Of Energy POWER

Rate at which work is performed or energy is expended

t

Watt is the base unit of Power

One watt is equal to 1 joule of work per second

Types of Power

• Electrical Power

Uses electrical energy to do work

• Mechanical Power

Uses mechanical energy to do work (linear, rotary)

• Fluid Power

Uses energy transferred by liquids (hydraulic) and gases (pneumatic)

• Power is the rate that we use energy.
• Power = Work or Energy / Time
• P = W/t = F x d/t = F v
• The unit joule is too small .The bigger unit of energy called kilowatt hour (kW h) 1 kW h is the energy used in one hour

at the rate of 1000 J s-1 (or 1 kW).

1 kW h = 1 kW *1 h = 1000 W*3600 s = 3600000 J 1 kW h = 3.6 x 10⁶ J.

Test Yourself

1. A 5 Kg Cart is pushed by a 30 N force against friction for a distance of 10m in 5 seconds. Determine the Power needed to move the cart.
2. A student lifts a 50.0 pound (lb) ball 4.00 feet (ft) in 5 .00seconds (s). How many watts of power are used to lift the ball?

Important Points for Work Problems:

• Always draw a free-body diagram, choosing the positive x-axis in the same direction as the displacement.
• Work is negative if a component of the force is opposite displacement direction
• Work done by any force that is at right angles with displacement will be zero (0).
• For resultant work, you can add the works of each force, or multiply the resultant force times the net displacement.
• Energy is the ability to move
• Potential is stored energy (Statics)
• Dependant on height
• Kinetic is moving energy (Dynamics)
• Dependant on velocity
• Springs store energy dependant on distance and constant

QUESTION BANK

One mark questions

1. Does work have a direction?
2. Does the kinetic energy of an object depend on its direction of motion?
3. Cam matter be converted into energy?
4. Give an example of conversion of chemical energy into heat energy.

Two marks questions

1. Two persons do the same amount of work. The first person does it in 10 s and the second, in 20 s.Find the ratio of the power used by the person to that by the second person.
2. A body of mass 25 g has a momentum of 0.40 kgm/s.Find its kinetic energy.
3. Define work and write its units.
4. By what factor does the kinetic energy of an object depend on its direction of motion?

Three marks questions

1. How much time will it take to perform 440 j of work at a rate of 11 W.
2. A body of mass 3.0kg and a body B of mass 10 kg are dropped simultaneously from a height of 14.9m.Calculate their Momenta, their Potential energies and kinetic energies when they are 10m above the ground.
3. lA man does 200j ofl work in 10 seconds and a boy does 100j of work in 4 seconds. Who is delivering more power? Find the Ratio of power delivered by the man to that by the boy.

Five marks questions

1. Show that the work done by a force is given by the product of the force and the projection of the displacement along the force.
2. Find the expression for gravitational potential energy of a body of mass m at height h.
3. Why does a person standing for a long time get tired when he does not appear to do any work?
4. How can you justify that a body kept at a greater height has larger energy?

CHAPTER 10- “GRAVITATION”

KEY CONCEPTS [ *rating as per the significance of concept]

1	Gravitation	***
2	Universal Law Of Gravitation	****
3	Free Fall	**
4	To Calculate The Value Of G	****
5	Mass & Weight	***
6	Weight Of The Object On Moon	***
7	Thrust & Pressure	***
8	Pressure In Fluids	***
9	Buoyancy	****
10	Why Objects Float Or Sink When Placed On The Surface Of Water?	***
11	Archimedes’s Principle	*****
12	Relative Density	***

Gravity is one of the most basic forces in the universe. It plays a fundamental role not only in the structure of our solar system but also in the way objects behave on Earth. In this section, we will talk about gravity on a small scale. We will discuss topics such as weight, free fall, and ballistics. We will learn the physics of phenomena we experience daily and take for granted

1.Gravitation

Gravitation is the force of attraction between two objects in the universe.

Gravitation may be the attraction of objects by the earth.

This force is proportional to the product of masses of the objects and inversely proportional to the square of the distance between them. It is independent of medium.

_ , , GMm

Gravitational force = ——

r^z

Eg If a body is dropped from a certain height, it falls downwards due to earth’s gravity.

If a body is thrown upwards, it reaches a certain height and then falls downwards due to the earth’s gravity.

• Gravitation may be the attraction between objects in outer space.

Eg :- Attraction between the earth and moon.

Attraction between the sun and planets.

GRAVITY

• A natural force that pulls all objects toward the center of the earth
• keeps the moon orbiting
• It holds stars together . . .
• And binds galaxies together for billions of years ….Prevents Planets from losing their atmospheres.

Test yourself:

1. When we move from the poles to the equator. Hence, the value of g decreases. Why?
2. What is the difference between gravity and gravitation?

2.Universal law of gravitation: – “Inverse square law”- All bits of matter attract all other bits of matter

• The universal law of gravitation states that, ‘Every object in the universe attracts every other object with a force which is directly proportional to product of the masses and inversely proportional to the square of the distance between them.’
• The strength of the gravitational attraction between two objects depends on two factors:

• The SI unit of G is N m² kg ^-2 and its value is 6.673 x 10^-11 N m² kg ^-2
• How big the objects are (how much mass they have) and
• How far apart they are.

Test Yourself

1. What is the difference between gravity and gravitation?
2. What does it mean to say that the Force of gravity is proportional to the masses

of the bodies, and inversely proportional to the distance between them?

3. Free Fall

• With negligible air resistance, falling objects can be considered freely falling. objects of different shapes accelerate differently (stone vs feather)

Test Yourself

1. A coin and a feather are dropped from the roof of a building. Which one will fall to the ground first

4 .To calculate the value of” g “(acceleration due to gravity)

• The acceleration due to gravity is denoted by g.
• The unit of g is same as the unit of acceleration ms ^-2
• From the second law of motion, force is the product of mass and acceleration.

F = ma

• For free fall, force is the product of mass and acceleration due to gravity.

GMm

F = mg or mg = =

GM

or g = — where M is the mass of the

Earth and d is the distance between the object and the earth.

• For objects near or on the surface of the earth d is equal to the radius of the earth R

GMm

• F = mg or mg = =

GM

• or g = —

Test Yourself

1. Calculate the value of g on the surface of earth.
2. What is the difference between “weight” and “mass”?
3. Mass and Weight:

• Mass is a fundamental, universal property. You have the same amount of mass no matter where you are in the Universe.
• Weight is not fundamental its value depends on circumstances in the Universe. Weight is a force. It is the resultant gravitational force exerted on a body with mass m by all the other bodies on the Universe.

Weight = F_g = G m M_e / R² = mg where M_e is the mass of the Earth and R is the radius of the Earth.

Test Yourself

1. An astronaut has 80 kg mass on earth (a)what is his weight on earth? (b) What

will be his mass and weight on mars where g=3.7 m/s² ‘

1. When you put an object on a spring balance, do you get the mass of an object or its weight?
2. 
   Weight Of The Object On Moon

• The mass of the moon is less than the mass of the earth. So the moon exerts lesser force on the objects than the earth.
• The weight of an object on the moon is one sixth (1/6^th) of its weight on the earth.
• The weight of an object on the earth is the force with which the earth attracts the

object and the weight of an object on the moon is the force with which the moon attracts the object.

Celestial body	Mass (kg)	Radius (m)
Earth	5.98 x 1024	6.37 x 106
Moon	7.36 x 1022	1.74 x 106

Test Yourself

1. What will be the weight of the body on the moon whose mass is12 kg?
2. 
   Thrust & Pressure

• Thrust is the force acting on an object perpendicular to the surface.
• Pressure is the force acting on unit area of a surface

Thrust

Pressure =

Area

• The SI unit of thrust is N/m² or N m^-2 . It is called Pascal (Pa).

1. Pressure In Fluids

• . Fluids exert pressure in all directions
• Pressure exerted on fluids is transmitted equally in all directions.

1. Buoyancy

When an object is immersed in a fluid it experiences an upward force called buoyant force. This property is called buoyancy or upthrust.

1. Why objects float or sink when placed on the surface of water?

• Take some water in a beaker. Take a piece of cork and an iron nail of the same mass. Place them on the water. The cork floats and the nail sinks.
• If the density of an object is less than the density of a liquid, it will float on the liquid and if the density of an object is more than the density of a liquid, it will sink in the liquid.

1. Archeimedes Principle

• Archimedes’ principle states that, When a body is partially or fully immersed in a fluid it experiences an upward force that is equal to the weight of the fluid displaced by it.’

12 .Relative density

• The relative density of a substance is the ratio of the density of a substance to the density of water. It is a ratio of similar quantities and has no unit.

QUESTION BANK

One Mark questions

1. Explain what Centrifugal force is.
2. What do you mean by the weight of the body on moon.
3. Give the value of G with proper units.
4. Give the value of g with proper units.
5. What is measured by physical balance?

Two Marks questions

1. At what height above the earth’s surface would the value of acceleration due to gravity be half of what it is on the surface? Take radius of earth to be R.

2 . A body of 90 kg f on the surface of earth. How much will it weigh on the surface of moon whose mass is 1/9 and radius is V of that of earth?

1. A piece of paper takes much longer to fall than a stone through the same distance. Explain the reason.
2. Consider a heavenly body which has a mass twice that of the earth and radius thrice that of the earth .What will be the weight of the book on this heavenly body, if its

weight on earth is 900 N?

Three Marks questions

1. Why gravitational force is usually unnoticeable?
2. Prove that acceleration due to gravity is independent of mass of the body.
3. How can the average density of the earth can be determined?
4. What is buoyancy and buoyant force? Upon what factors do they depend Five Marks questions
5. Find the percentage change in the weight of a body when it is taken from equator to poles. The polar radius is 6,357 Km and equatorial radius is 6,378 Km.
6. The density of ice is 918kgm-3 and that of sea water is 1,030kgm-3.An iceberg floats with a portion 224 liters outside water. Find the volume of iceberg.
7. What are the laws of flotation? Give some illustrations.

CHAPTER -9 “Force & Laws Of Motion”

KEY CONCEPTS [ *rating as per the significance of concept]

1	Balanced and Unbalanced Forces	***
2	Laws of Motion	*****
3	Inertia and Mass	*****
4	Conservation of Momentum	****

The Effect of Mass

A force applied to an automobile will not have the same effect as the same force applied to a pencil. An automobile resists accelerating much more than a pencil does, because it has more inertia, or mass.

The acceleration of an object depends not only on how hard you push on it, but also on how much the object resists being pushed.

What is the effect of mass on acceleration? This, too, turns out to be quite simple (I wonder why…). For the same force, an object with twice the mass will have half the acceleration. If it had three times the mass, the same force will produce one-third the acceleration. Four times the mass gives one-fourth of the acceleration, and so on.

This type of relationship between quantities (double one, get half the other) is called an inverse proportion or inverse variation. In other words, then:

Newton’s Second Law of Motion The acceleration of an object is dependent upon both force and mass. Thus, if the colliding objects have unequal mass, they will have unequal accelerations as a result of the contact force which results during the collision.

Newton’s Third Law Newton’s Third Law is stated as:

For every action there is an equal and opposite reaction.

“action…reaction” means that forces always occur in pairs. (Forces are interactions between objects, like conversations are interactions between people.)

Single, isolated forces never happen. The two forces involved are called the “action force” and the “reaction force.”

These names are unfortunate for a couple of reasons :

Either force in an interaction can be the “action” force or the “reaction” force

The action and reaction forces exist at the same time.

“equal” means

Both forces are exactly the same size. They are equal in magnitude.

Both forces exist at exactly the same time. They both start at exactly the same instant, and they both stop at exactly the same instant. They are equal in time.

“opposite” means that the two forces always act in opposite directions – exactly 180^o apart.

Newton’s third law of motion In every interaction, there is a pair of forces acting on the two interacting objects. The size of the force on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs – equal and opposite action- reaction force pairs.

Newton’s third law of motion applied to collisions between two objects. In a collision between two objects, both objects experience forces which are equal in magnitude and opposite in direction. Such forces cause one object to speed up (gain momentum) and the other object to slow down (lose momentum). According to Newton’s third law, the forces on the two objects are equal in magnitude.

Test Yourself

1. Can action reaction balance each other?
2. What does a force do?
3. 
   Inertia and Mass

Inertia is the tendency of an object to resist any change in its motion. An object will continue to move at the same speed in the same direction

unless acted upon by an unbalanced force. Inertia & Mass Inertia & Mass of a bowling ball rolled down the road would eventually come to a stop. Friction is an unbalanced force that causes the ball to stop or slow down. Without friction, the ball would keep going.

Inertia & Mass of a bowling ball and a tennis ball have the same inertia. Inertia & Mass If you had a tennis racket and I threw tennis ball at you, what would happen? If you had a tennis racket and I threw a bowling ball at you, what would happen? Why could you change the motion of the tennis ball but not the motion of the bowling ball?

Mass is the amount of matter in an object. A bowling ball has more mass than a tennis ball. The greater the mass of an object the greater its inertia. Mass is the measurement of inertia.

Test Yourself

1. Why do we fall forward if we alight from a moving bus?
2. Why does an athlete run for some distance before long jump?
3. Conservation of Momentum

Law of Conservation of Momentum

In a closed system, the vector sum of the momenta before and after an impact must be equal.

Before After

m₁v₁ +m₂v₂ = m₁v₁‘ + m₂v₂‘

Internal and External Forces

QUESTION BANK

One Mark questions

1. Define momentum.
2. State first law of motion.
3. What is inertia?
4. Can action and reaction balance each other?
5. How does one climb up a rope?
6. Why cannot we walk in space?
7. What does rate of change of momentum represent?
8. Why do we continuously paddle to keep the cycle moving?
9. Why does a scooter tend to skid while executing a sharp turn?
10. Which one would have more inertia : 10 kg mass & 5 kg mass?

Two Marks questions

1. Explain the functioning of shockers in cars.
2. How much force is needed to pull an object of mass 40 kg in vertically upward direction with acceleration of 2.2 m / s².
3. Why does a fan keep moving for sometime when switched off?
4. What do you mean by conservation of momentum?
5. Inflated balloon lying on the surface of a floor moves forward when pricked with a pin. Why?

Three Marks questions

1. An iron sphere of mass 10 kg is dropped from a height of 80 cm, if ‘g’ = 10 m / s². Calculate the momentum transferred to the ground by the body.
2. What would be the force required to stop a car of mass 1000 kg and a loaded truck of mass 10,000 kg in 2 seconds each moving with velocity 5 m / s.
3. Deduce law of conservation of momentum using third law of motion.

Five Mark questions

1. Name and define three different types of inertia & give an example of each.