Q & A OF THRUST AND PRESSURE

The total force acting perpendicular on a given surface is called thrust. Thrust acting upon a unit area is called pressure. Its S.I. unit is Pascal denoted by ‘P’ Thus, pressure =Thrust/Area of contact Archimedes’ principle states that when a body is immersed partially or fully in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it. Archimedes' Principle is used in designing ships and submarines. The Lacto meters and hydrometers used for measuring the purity of a sample of milk and for determining the density of the liquids are based on this principle. Buoyancy can be defined as the tendency of the fluit to exert an upward force on an object, which is wholly or partially immersed in a fluid.

The S.I. unit of buoyant force is Newton.

This upward force that acts on an object when immersed in a fluid is called buoyant force.

Two main factors on which the buoyant force depends are:   (i) Density of the fluid. (ii) Value of acceleration due to gravity at that place.

When an iron nail is placed on the surface of water it sinks whereas ship made up of iron floats. This is because size or volume of the ship is more.

 If the density of the liquid is more than the density of the material of the body then the body floats due to the buoyant force exerted by it and vice-versa.

Density of a substance is the mass of the substance contained in a unit volume of that substance.

Density of an object is given as Mass/Volume 

Buoyant force experienced by a body when submerged in a liquid depends on the volume of the body and the density of the liquid.

The density of a substance is one of its characteristic properties and used to determine the purity of any substance.

Floating and Sinking depends on density of water and the density of an object

If the density of an object is less than the density of water it floats. This means that the up thrust of water on an object is greater than the weight of the object. 

If the density of an object is more than the density of water it sinks. This means that the up thrust of water on an object is less than the weight of the object. 

Therefore objects of density less than that of a liquid float on the liquid. The objects of density greater than that of a liquid sink in the liquid.

Two forces act on an object immersed in water. One is the gravitational force, which pulls the object downwards, and the other is the buoyant force, which pushes the object upwards.

If the upward buoyant force is greater than the downward gravitational force, then the object comes up to the surface of the water 

The density of the substance is more than the density of water ( 1 g/ cm3) than it will sink in water. 

Relative density of a substance is the ratio of density of substance to the density of water. It is also called specific gravity.

Relative density = Density of substance/density of water

Relative density of a substance help us determine the purity of a substance by measuring its relative density   Examples:  We use lactometer to differentiate between pure and impure(measure the impurity) milk. We can measure the impurity of water using hydrometer.

What is meant by the statement relative density of gold is 19.3? 

It means that gold is 19.3 times denser than an equal volume of water. Those objects whose relative density is less than one will float in water and those greater than one will sink.

5 kg of cotton occupies more space than 5 kg of iron. The particles of iron are closely packed while that of cotton are loosely packed. The amount of iron packed in a unit volume is more. This explains as to why iron is heavier than the same volume of cotton.

In Physics, word density help us to describe the lightness or heaviness of different substances 

Why is it difficult to hold a school bag having a strap made of a thin and strong string?

It is difficult to hold a school bag having a strap made of a thin and strong string because it apply the large pressure on the shoulders due to very small contact surface area . we know that the pressure is inversely proportional to the surface area on which the force acts

Why is it difficult to hold a school bag having a strap made of a thin and strong string?

It is difficult to hold a school bag having a strap made of a thin and strong string because it apply the large pressure on the shoulders due to very small contact surface area . we know that the pressure is inversely proportional to the surface area on which the force acts

What do you mean by buoyancy?

The tendency of a liquid to exert an upward force on an object placed in it is called buoyancy. 
When a body is completely or partially immersed in a fluid, then the upward thrust acting on the body is called force of buoyancy or buoyant force.

It increases as we push the object deeper into water. The magnitude of this buoyant force depends on the density of the fluid.

Why does an object float or sink when placed on the surface of water?

An object floats or sinks when placed on the surface of water because of the buoyant force acting on the object.

If the density of an object is less than the density of water it floats. This means that the up thrust of water on an object is greater than the weight of the object.

If the density of an object is more than the density of water it sinks. This means that the up thrust of water on an object is less than the weight of the object.

Therefore objects of density less than that of a liquid float on the liquid. The objects of density greater than that of a liquid sink in the liquid.

Why the cutting edge of a knife should be as sharp as possible? 

The cutting edge of a knife should as sharp to create greater pressure even for a very small applied force for quick action.

You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

When we weight our body, a downward ward gravitational force acts on it. Hence our actual mass is less than 42 kg
You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?

In reality, a bag of an iron bar is heavier than a bag of cotton.Each indicating a mass of 100 kg when measured on a weighing machine as more gravitational force act on a bag of cotton due to its larger the surface area.

In what direction does the buoyant force on an object immersed in a liquid act?

Ans: The buoyant force acts on an object in the vertically upward direction through the center of gravity of the displaced liquid. 

Why does a block of plastic released under water come up to the surface of water?

A block of plastic released under water come up to the surface of water because the up thrust or the buoyant force exerted by the water is greater than the downward gravitational force. 

The volume of 50 gm of a substance is 20 cm³. If the density of water is 1 g/cm³, will the substance float or sink?

Given the mass of the substance = 50 g     Volume of the substance = 20 cm³

Density of substance = Mass /Volume = (50 /20) g/cm³ = 2.5 g/cm³

Since the density of the substance 2.5 g/cm³ is greater than the density of water (1 g/cm³), so the substance will sink in the water.

The volume of a 50 gm sealed packet is 350 cm³. Will the packet float or sink in water if the density of water is 1 g/cm³ ? What will be the mass of the water displaced by this packet  ?

Mass of packet = 500 g               Volume of packet = 350 cm³

Density of packet = Mass ÷ Volume = (500 / 350) g/cm³ = 1.43 g/cm³

The sealed packet will sink in the water as its density 1.43 g/cm³ is more than that of water.

The volume of water that will be displaced by the packet = 350 cm³

And mass of this displaced water = Volume x Density = 350 x 1 = 350 gm.


State Archimedes’ principle. Give any two applications of Archimedes principle?

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

The two applications of Archimedes principle are given below: 
(i) Floating of ships and submarines (ii) The lactometers to test purity of milk

How do a submarine sink and float on water?

A submarine can both sink and float on water because of the ballast tank . 

To make a submarine sink into the water, these tanks are filled with water. This increases the weight of the submarine and it sinks. 
To make a submarine float on the water surface, these tanks are emptied by pumping out water from them. This decreases the weight of the submarine and it floats

notebook work of why do we fall ill tabular form write acc to correct page no

notebook hw for natural resources

1) Explain  resources on the earth

Ans:    The natural resources of the earth are air, water, soil, minerals and living organisms.    The outer crust of the earth is the lithosphere. The water on the earth is the hydrosphere. The layer of the air around the earth is the atmosphere. Living organisms are found where the atmosphere, hydrosphere and lithosphere interact and is the biosphere.



2. write a note on Air (Atmosphere)

Ans:   Air is a mixture of gases like nitrogen, oxygen, carbon dioxide, water vapour and other gases.

Ø During respiration living organisms use oxygen to break down glucose and get energy for their activities. This results in the release of carbon dioxide. Burning of fuels also use oxygen and release carbon dioxide.

Ø During photosynthesis green plants convert carbon dioxide into glucose in the presence of sunlight. This results in the release of oxygen.

Ø These processes help to maintain the oxygen – carbon dioxide balance in nature.

3. Explain  the role of atmosphere in climate control

Ø The atmosphere covers the earth like a blanket. Air is a bad conductor of heat. It prevents sudden increase in temperature during the day and also slows down the escape of heat during the night. So the atmosphere keeps the average temperature of the earth fairly steady during the day and throughout the year.

4. Write a note on  the movement of air (Winds)

Ø When air gets heated, it rises up and produces low pressure and cool air moves in to take its place. The movement of air causes winds.

Ø During the day the land gets heated faster than the sea. So the hot air above the land rises up and cool air from the sea moves towards the land. During the night sea cools down slowly than the land. So the hot air above the sea rises up and cool air from the land moves towards the sea.

5. How does   Rain occur?

Ø When water bodies are heated during the day, a large amount of water evaporates and rises up. Some water vapour also get into the atmosphere due to biological activities like transpiration. As the water vapour rises, it cools and condenses to form tiny droplets of water. This appears as clouds. When the tiny droplets of water join together to form bigger drops of water, they fall down as rain, snow or hail.

6. write a note on  Water : A wonder liquid :-

Ø A very large area of the earth’s surface is covered with water. Water is also found inside the earth, in the atmosphere as water vapour. The water in seas and oceans is saline. Fresh water is found in rivers, lakes, ponds and as ice and snow at the poles and mountains in cold regions.

Ø Water is needed by living organisms because all life processes and cellular activities need water. So all organisms need water to survive.

Ø The amount of water and other factors like temperature and nature of soil decides the diversity of species and the number of individuals of each species in an area.

7.  how does  Water pollution get polluted?

Ø The increase in the content of harmful substances in water is called water pollution.

Ø Water pollution is caused by addition of harmful substances like fertilisers and pesticides from farms, sewage from towns, cities and factories, harmful chemicals from factories, disease causing microorganisms, changes in the amount of oxygen dissolved in water or changes in the temperature of water.

 

8. How is soil formed?

Ø Soil is formed by the breaking down of rocks on the surface of the earth by physical, chemical and biological processess.

Ø The sun heats the rocks during the day and the rocks expand and at night the rocks cool and contracts. This causes the rocks to crack and break into smaller pieces.

Ø Water enters the cracks in the rocks and when water freezes, it expands and causes the cracks in the rocks to widen and break into smaller pieces. The flowing water carries the rock pieces. These pieces  rub against each other and become smaller and smaller particles.

Ø Strong winds also breaks rocks into smaller particles and carries it from one place to the other.

Ø The roots of large trees grow into the cracks in rocks and breaks it into smaller pieces. Lichens which grow on rocks produce some substance which cause the rock surface to powder and become soil.

9. Explain composition of soil :-

Ø Soil is a mixture of rock particles, decayed organisms called humus, living organisms, minerals, air and water. The amount of minerals, humus, air and water are the factors which decides the biodiversity in that area.

10. How does Soil  get polluted ?

Ø The addition of harmful substances which affects the fertility of the soil and kills the diversity of organisms living in it is called soil pollution.

Ø Soil pollution is caused by the excessive use of fertilisers and pesticides. It kills the organisms like earthworms and bacteria which makes the soil rich in humus. The removal of useful components and addition of other harmful substances reduces the fertility of soil and causes soil pollution.



11. Explain  Soil erosion and its prevention?

Ø The carrying away of soil from one place to the other by flowing water and wind is called soil pollution. Large scale deforestation also causes soil erosion.



Ø Soil erosion can reduced or prevented by vegetative cover on the ground, afforestation, construction of bunds, terraces, dams etc.

12. What is  Biogeochemical cycles and name different biogeochemical cycles

Ø Biogeochemical cycles are the transfer of matter and energy between the biotic and abiotic components of the biosphere.

   The common biogeochemical cycles are :-

  i) Water cycle,

 ii) Nitrogen cycle,

iii) Carbon cycle

iv) Oxygen cycle.

13. Write a note on Water cycle

Ø When water bodies are heated during the day, a large amount of water evaporates and rises up. Some water vapour also get into the atmosphere due to biological activities like transpiration and respiration. As the water vapour rises, it cools and condenses to form tiny droplets of water. This appears as clouds. When the tiny droplets of water join together to form bigger drops of water, they fall down as rain, snow or hail. Some of this water enters the ground and forms ground water. When water flows from the land to the seas it carries many nutrients and minerals which are used by marine organisms.
Draw cycle from text book

14. Explain about Nitrogen cycle

Ø The nitrogen in the atmosphere is fixed into nitrogen compounds in the soil by nitrogen fixing bacteria in the root nodules of leguminous plants and also during lightning. These nitrogen compounds are taken by plants and used to make proteins. When animals eat plants they also get proteins. When plants and animals die, bacteria convert the proteins into nitrogen compounds like nitrites and nitrates. Other bacteria convert these nitrogen compounds back into nitrogen in the atmosphere.

Ø Nitrogen is an essential component of biological molecules like proteins, nucleic acids and some vitamins.


Draw cycle from text book


15.  Explain Carbon cycle

Ø Carbon in the form of carbon dioxide is used by plants to prepare glucose by the process of photosynthesis. The glucose is used to provide energy and to convert into other organic compounds When animals eat plants it enters the body of animals. During respiration energy and carbon dioxide are produced. The carbon dioxide goes back into the atmosphere. Another process which adds carbon dioxide back into the atmosphere is the combustion of fuels like coal and petroleum. The organic compound in plants and animals are also converted into carbonates, limestone, coal, petroleum, exoskeletons (shells) of some animals.

Ø Carbon is an essential component of biological molecules like carbohydrates, fats, proteins, vitamins, nucleic acids etc.

     draw cycle from text book

16. Explain  Oxygen cycle

    Oxygen in the atmosphere is used for respiration, combustion and formation of oxide of elements. Oxygen is sent back into the atmosphere during photosynthesis.

   Oxygen is an essential component of biological molecules like carbohydrates, fats, and proteins.

Draw cycle from text book





17.  Explain  the greenhouse effect

Ø Gases like carbon dioxide, methane, chlorofluro carbon(CFCs) traps the heat radiated by the earth and prevents the escape of heat from the earth. The increase in the presence of these gases in the atmosphere causes increase in the temperature of the atmosphere. This is called the greenhouse effect.

Ø Greenhouse effect can cause melting of polar ice, increase in sea levels, flooding of coastal areas and submerging of islands.

18. Explain Ozone layer

Ø Ozone molecule contains three atoms of oxygen (O3). It is present in the upper layers of the atmosphere. It is  poisonous gas. It protects the earth from the harmful ultra-violet radiations from the sun which is harmful for living organisms.

Ø The ozone layer is being damaged by carbon compounds like chloro fluoro carbons (CFCs). To prevent the damage to the ozone layer, the use of (CFCs) is being reduced.

notebook question and answers for why do we fall ill.

Answer the following questions

1. Define health

 Ans. Health is defined as State of being well enough to function well physically, mentally and socially.

2. Write difference between being healthy and diseases free.

	Healthy	Disease free
1.	It is a state of physical, mental and social well being.	It is a state of absence from diseases.
2.	It refers to the individual, physical and social environment.	It refers only to the individual.
3.	The individual has good health.	The individual may have good health or poor health.

3. Give significance of good health

4. Write conditions necessary for good health

Ans- i) Good  social environment + physical health

ii) Individual and public cleanliness.

iiI) Good economic conditions. 

iv) Social equality and harmony.

5. Explain symptoms and signs

➢ A symptom is a change in the normal structure or functioning of the body parts. this  indicate that there is some thing wrong in the body .

For e.g. fever, headache, body ache, stomachache, nausea or vomiting are all symptoms of presence of some disease

Signs are definite clues or indication of a specific disease. Medical test provide the correct diagnois of the diseases

6. Explain about 4 different types of diseases

➢ Diseases are of different types. They are :-

i) Acute diseases :-  are diseases which last only for a short period of time and does not have long term effect on health.

   Eg:- cold,  cough, typhoid, cholera etc

ii) Chronic disease :- are diseases which lasts for a long time and has long term drastic effect on health.

   Eg :- asthma, diabetes, tuberculosis, glucoma, elephantiasis, allergy, cancer etc.  

iii) Infectious diseases (Communicable diseases) :- are 

diseases which spread from an infected person to a healthy person through air, water, food, vectors, physical contact or sexual contact. Eg :- common cold, chicken pox, mumps, measles, typhoid, cholera, tuberculosis, malaria, AIDS etc.

iv) Non-infectious diseases (Non-communicable diseases) :- 

are diseases which are not spread from an infected person to a healthy person. Eg :- beri beri, rickets, scurvy, night blindness, diabetes, cancer, high blood pressure etc.

7. Explain causes of a diseases

Ans- Diseases are caused by :-

 i) Pathogens like virus, bacteria, fungi, protozoans or 

    worms.

ii) Poor health and under nourishment.

iii) Malfunctioning of body parts.

iv) Environmental pollution.

v) Genetic disorders

8. Make a list of infectious agents and diseases caused by them

Ans  - 1.Viruses-Common cold, Influenza, Measles, Mumps, Chicken pox, AIDS, Hepatits-B etc.

2.Bacteria-Cholera, Typhoid, Tuberculosis, Tetanus, Anthrax, Food poisoning etc.

3.Fungi-Skin infections.

4.Protozoans-Malaria, Kala-azar, Amoebic dysentry, Sleeping sickness.

5.Worms-Intestinal infections, Elephantiasis.

9. Make a list of infectious agents and diseases caused by them

1.Viruses-Common cold, Influenza, Measles, Mumps, Chicken pox, AIDS, Hepatits-B etc.

2.Bacteria-Cholera, Typhoid, Tuberculosis, Tetanus, Anthrax, Food poisoning etc.

3.Fungi-Skin infections.

4.Protozoans-Malaria, Kala-azar, Amoebic dysentry, Sleeping sickness.

5.Worms-Intestinal infections, Elephantiasis.

10. Explain Means of spread of infectious diseases

Ans:     Infectious diseases spread from an infected person to a healthy person through air, water, food, vectors, physical contact and sexual contact.

 i) Through air :- Common cod, Tuberculosis, Pneumonia 

                            etc.

ii) Through water :- Cholera, Amoebic dysentry etc.

iii) Through vectors :-

   Mosquitoes :- Malaria, Dengue, Yellow fever etc.

   Flies             :- Typhoid, Tuberculosis, Diarrhoea, Dysentry

                          etc.

iv) Through sexual contact :- Syphilis, AIDS.

  AIDS virus can also spread though blood transfusion and from  the mother to her child during pregnancy and through breast feeding.

11. Explain Organ-specific and tissue-specific 
   manifestations

Ans: Disease causing microbes enter the body by different means and goes to different organs and tissues.

i) Microbes which enters through the nose are likely to go to the lungs. ( Bacteria which cause tuberculosis of lungs). 

ii) Microbes which enter through the mouth are likely to stay in the gut ( Bacteria which causes Typhoid) or liver (Bacteria which causes Jaundice).

iii) Virus which causes AIDS enter the body through sexual organs during sexual contact and spreads through the lymph to all parts of the body and damages the immune system.N

iv) Virus which causes Japanese encephalitis (brain fever) enters the body through mosquito bite and goes and infects the brain.

12. Write Principles of treatment :-

Ans : The treatment of infectious diseases consists of two steps. They are to reduce the effects of the disease (symptoms) and to kill the microbes which caused the disease.

i) To reduce the effects of the disease :- 

  This can be done by taking medicines to bring down the  effects of the disease like fever, pain or loose motions etc. and by taking bed rest to conserve our energy.

ii) To kill the microbes :-

This can be done by taking suitable antibiotics and drugs which kills the microbes and the disease is cured.

13. Write principles of prevention.

  There are two ways of prevention of infectious diseases. They are general ways and specific ways.

i) General ways of prevention :-

   Public hygiene is most important for prevention of infectious diseases. Proper and sufficient food for every onewill make people healthy to resist infection.

  Air borne diseases can be prevented by living in conditions that are not crowded. Water borne diseases can be prevented by providing safe drinking water. Vector borne diseases can be prevented by providing clean environment.

ii) Specific ways of prevention :-

  The specific ways to prevent infectious disease is  immunisation by taking vaccines. Vaccines provide immunity from infectious diseases like tetanus, diphtheria, whooping cough, measles, polio etc. 

  Our body has an immune system which fights microbial infection. When this system first sees an infectious microbe, it kills the microbe and remembers it. So if the microbe enters the body the next time, it responds more vigorously. Vaccines mimic the infectious microbe  and strengthens our immune system and protects the body from infectious diseases. 

14. What is immunization?

15. Write about  disesese caused by protozonas, fungi ,bacteria , viruses and worms and its symptoms and preventive measures.