Solutions of Class 8 Chapter 11 (Force and Pressure)

 Exercise Questions

1. Give two examples each of situations in which you push or pull to change the state of motion of objects

Soln:

Examples of situations in which you push or pull to change the state of motion of objects.

1. Pull situations

a) In order to open a drawer, we have to pull it. This action changes the state of motion of the drawer.

b) To draw water from the well, the rope is pulled. This action changes the state of motion of the bucket.

2. Push Situations

a) A football is pushed by the foot of a player. This action changes the state of motion of the ball.

b) In order to change the place of the heavy box from one room to another, we have to push it. This action changes the motion of the box.

2. Give two examples of situations in which applied force causes a change in the shape of an object.

Soln:

The forces which change the shape of an object are as follows:

i) By pressing the clay between the hands, it deforms.

ii) The shape of the plastic bottle changes by squeezing it.

3. Fill in the blanks in the following statements.

(a) To draw water from a well we have to __________ at the rope.

(b) A charged body __________ an uncharged body towards it.

(c) To move a loaded trolley we have to __________ it.

(d) The north pole of a magnet __________the north pole of another magnet.

Soln:

1. To draw water from a well we have to pull at the rope.
2. A charged body attracts an uncharged body towards it.
3. To move a loaded trolley we have to pull or push it.
4. The north pole of a magnet repels the north pole of another magnet.

4. An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms.

muscular, contact, non-contact, gravity, friction, shape, attraction

(a) To stretch the bow, the archer applies a force that causes a change in its __________.

(b) The force applied by the archer to stretch the bow is an example of __________ force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a __________ force.

(d) While the arrow moves towards its target, the forces acting on it are due to __________ and that due to __________ of air

Soln:

(a) To stretch the bow, the archer applies a force that causes a change in its shape.

(b) The force applied by the archer to stretch the bow is an example of muscular force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a contact force.

(d) While the arrow moves towards its target, the forces acting on it are due to gravity and that due to friction of air.

5. In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

(a) Squeezing a piece of lemon between the fingers to extract its juice.

(b) Taking out paste from a toothpaste tube.

(c) A load suspended from a spring while its other end is on a hook fixed to a wall.

(d) An athlete making a high jump to clear the bar at a certain height

Soln:

a) We make a muscular force to extract the juice of the lemon by squeezing it. As a result, the shape of the lemon gets changed.

b) To take out paste from the toothpaste tube we use our muscular force. This muscular force acting on the toothpaste tube leads to a change of its shape.

c) Here, the suspended load exerts a force on the spring and pushes the spring downwards. As a result, the spring gets stretched. Hence, its shape gets changed.

d) The feet of the athlete exert the muscular force on the ground, which pushes the ground. This allows him to jump over the bar. As a result, his state of motion gets changed.

6. A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Soln:

A blacksmith uses his muscular force while hammering a hot piece of iron. The muscular force changes the shape of the iron so that it can be given the desired shape.

7. An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

Soln:

When an inflated balloon rubbed with a piece of synthetic cloth, it becomes charged. A charged body attracts an uncharged body. When this charged balloon is pressed against a wall, it sticks to the wall. Thus, the electrostatic force acts between the charged balloon and the wall.

8. Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.

Soln:

For holding the bucket of water above the ground, we use muscular force. This muscular force acts against the force of gravity that pulls the bucket towards the ground. The two forces are equal in magnitude but opposite in direction. Therefore, the net force on the bucket is zero. Hence, there is no change in the state of motion.

9. A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.

Soln:

The force of gravity is the one which acts on the rocket to pull it towards the ground and the other one is the force of friction due to earth’s atmosphere, which opposes its motion.

10. When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to

(a) pressure of water.

(b) gravity of the earth.

(c) shape of rubber bulb.

(d) atmospheric pressure

Soln:

a) Due to the atmospheric pressure, there is a rise of water in the dropper.

When all the air escapes from the nozzle, the atmospheric pressure which is acting on the water forces the water to fill the nozzle of the dropper.

Solutions for Class 6 Chapter 8 (Body Movements)

 Exercise Questions

1. Fill in the blanks:

(a) Joints of the bones help in the ——————— of the body.

(b) A combination of bones and cartilages forms the _______ of the body.

(c) The bones at the elbow are joined by a ______________________ joint.

(d) The contraction of the _____________ pulls the bones during movement.

Solution:

(a) Joints of the bones help in the movement of the body.

(b) A combination of bones and cartilages forms the skeleton of the body.

(c) The bones at the elbow are joined by a hinge joint.

(d) The contraction of the muscles pulls the bones during movement.

2. Indicate true (T) and false (F) among the following sentences.

(a) The movement and locomotion of all animals is exactly the same. ( )

(b) The cartilages are harder than bones. ( )

(c) The finger bones do not have joints. ( )

(d) The fore arm has two bones. ( )

(e) Cockroaches have an outer skeleton. ( )

Solution:

a) False

b) False

c) False

d) True

e) True

3. Match the items in Column I with one or more items of Column II.

Solution:

Column I	Column II
Upper jaw	Have fins on the body
Fish	Has an outer skelton
Ribs	Can fly in the air
Snail	is an immovable joint
Cockroach	Protect the heart
	Shows very slow movement
	Have a streamlined body

Solution:

Column I	Column II
Upper jaw	is an immovable joint
Fish	Have fins on the body, Have a streamlined body
Ribs	Protect the heart
Snail	Has an outer skeleton and Shows very slow movement
Cockroach	Has an outer skeleton and Can fly in the air

4. Answer the following:

(a) What is a ball and socket joint?

(b) Which of the skull bones are movable?

(c) Why can our elbow not move backwards?

Solution:

a) The rounded end of one bone fits into the cavity (hollow space) of the other bone. Such a joint allows movements in all directions, which is called ball and socket joint.

b) Lower jaw

c) Our elbow cannot move backwards because it has hinge joints which only allow back and forth movement.

Solutions of Getting to Know Plants, Ch 7, Class 6

 1. Correct the following statements and rewrite them in your notebook.

(a) Stem absorbs water and minerals from the soil.

(b) Leaves hold the plant upright.

(c) Roots conduct water to the leaves.

(d) The number of petals and stamens in a flower is always equal.

(e) If the sepals of a flower are joined together, its petals are also joined together.

(f) If the petals of a flower are joined together, then the pistil is joined to the petal.

Solution:

a) Roots absorbs water and minerals from the soil.

b) Stem holds the plant upright.

c) Stems conduct water to the leaves.

d) The number of petals and stamens in a flower may not be always equal.

e) If the sepals of a flower are joined together, its petals are separate.

f) If the petals of a flower are joined together, then the pistil may or may not be joined to the petal.

2. Draw (a) a leaf, (b) a taproot and (c) a flower, you have studied for Table 7.3

Solution:

a)

b)

c)

3. Can you find a plant in your house or in your neighborhood, which has a long but weak stem? Write its name. In which category will you place it?

Solution:

Yes, lauki (gourd) plant needs support. It is a climber.

4. What is the function of a stem?

Solution:

Following are the functions of a stem

• Stem holds the plant upright.
• Stems conduct water to the leaves.
• Stems conduct food from leaves to other parts of the plant.

5. Which of the following leaves have reticulate venation?

Wheat, tulsi, maize, grass, coriander (dhania), China rose

Solution:

Tulsi, China rose and coriander have reticulate venation.

6. If a plant has fibrous root, what type of venation do its leaves have?

Solution:

If a plant has fibrous root, its leaves have parallel venation.

7. If a plant has leaves with reticulate venation, what kind of roots will it have?

Solution:

If a plant has leaves with reticulate venation, it will have tap root.

8. Is it possible for you to find out whether a plant has taproot or fibrous roots by looking at the impression of its leaf on a sheet of paper?

Solution:

Yes it is possible to find whether a plant has taproot or fibrous roots by looking at the impression of its leaf on a sheet of paper.

9. What are the parts of a flower?

Solution:

a) Sepals

b) Petals

c) Stamens

d) Pistil

10. From the following plants, which of them have flowers?

Grass, maize, wheat, chilli, tomato, tulsi, peepal, shisham, banyan, mango, jamun, guava, pomegranate, papaya, banana, lemon, sugarcane, potato, groundnut

Solution:

The plants which have flowers are grass, maize, wheat, chilli, tomato, tulsi, peepal, shisham, banyan (flowers lie inside its fruits), mango, jamun, guava, Pomegranate, papaya, banana, lemon, sugarcane, potato, groundnut

11. Name the part of plant which produces food. Name the process.

Solution:

Leaves produce food through a process called as Photosynthesis.

12. In which part of a flower, you will find the ovary?

Solution:

Ovary is found in the lowermost and swollen part of the pistil.

13. Name two plants in which one has joined sepals and the other has separate sepals.

Solution:

Plants with joined sepals- Datura and cotton

Plants with separate sepals- Rose and Lotus

Solutions of Conservation of Plants and Animals, Ch 7 , Class 8

 Exercise Questions

1. Fill in the blanks.

(a) A place where animals are protected in their natural habitat is called _________.

(b) Species found only in a particular area is known as _______.

(c) Migratory birds fly to faraway places because of __________ changes.

Soln:

(a) A place where animals are protected in their natural habitat is called Sanctuary.

(b) Species found only in a particular area is known as endemic.

(c) Migratory birds fly to faraway places because of climatic changes.

2. Differentiate between the following.

(a) Wildlife sanctuary and biosphere reserve

(b) Zoo and wildlife sanctuary

(c) Endangered and extinct species

(d) Flora and fauna

Soln:

(a)

Wildlife sanctuary	Biosphere Reserve
An area within which wild animals are protected from external dangers like hunting	An area constructed for the conservation of biodiversity
Adequate habitat and protection are provided for the wild animals living in a sanctuary	Several life forms like plants, animals, and micro-organisms conservation are possible in a reserve
Eg: Corbett national park	Eg: Nilgiri Biosphere reserve

b)

Zoo	Wildlife Sanctuary
Animals are kept in artificially constructed facilities for public exhibition.	An area within which wild animals are protected from external dangers like hunting.
It is an artificial habitat and the animals may or may not adapt to the new conditions.	The animals are conserved within their natural habitat itself. So, they won’t have a problem with their surroundings.

(c)

Endangered Species	Extinct Species
The species which are on the verge of extinction are called as Endangered species.	The species of animals or plants that no longer exist are called Extinct species.
Eg: Bengal Tiger, Blue Whale, etc.	Eg: Caribbean monk seal, Great Auk, Passenger pigeon.

(d)

Flora	Fauna
It is the collective name for the plant life from a particular area.	It is the collective name for the animal life from a particular area
Eg: Spurge and Hogweed from the Nilgiris region	Eg: Langur, Tiger, Tahr from the Nilgiris region.

3. Discuss the effects of deforestation on the following.

(a) Wild animals

(b) Environment

(c) Villages (Rural areas)

(d) Cities (Urban areas)

(e) Earth

(f) The next generation

Soln:

(a) Effects of deforestation on wild animals:

Removal of trees and plant life from a particular area for the construction of industries, agriculture or for other such purposes is termed as Deforestation. Plantlife forms an integral part of the ecosystem and these plants form the natural habitat of various animals of that ecosystem. Destroying the plant life will ultimately threaten the existence of animals in that particular ecosystem and may lead to their extinction.

(b) Effects of deforestation on the environment:

In plants, Photosynthesis takes place by the absorption of CO2 from the earth’s atmosphere. The percentage of CO2 in the atmosphere increases rapidly if the plant life of an area is destroyed. Increased concentrations of CO2 result in the trapping of excessive heat radiations within the Earth’s atmosphere contributing to global warming. This results in the rise of the temperature of the Earth and disturbs the water cycle which occurs in nature. Hence, rainfall pattern changes leading to droughts and floods.

(c) Effects of deforestation on villages:

The soil particles are held together in a place by the roots of the plants, trees and other vegetation. In the event of water flow or a high-speed wind over the top layer of the soil, the soil particles get removed easily as there are no plants to hold it in place. Thus, soil erosion is increased by deforestation activities. Soil loses fertility and loses humus. Hence, a fertile land, fit for agriculture turns into a desert.

(d)Effects of deforestation on cities:

The risk of natural calamities like floods and drought in urban areas is increased by deforestation. It will also lead to global warming because of increased CO2 levels in the atmosphere. This is a result of continuous pollution from automobiles and industries. The water cycle in the vicinity is also affected.

(e) Effects of deforestation on Earth:

Deforestation leads to increased chances and occurrences of desertification, droughts and floods. Carbon Dioxide level in the earth’s atmosphere also increases which leads to global warming. The water cycle is disrupted and there is also an increased risk of natural calamities.

(f) Effects of deforestation on the next generation:

Our Environment is slowly changed by the activities of deforestation, both directly and indirectly. Soil erosion, global warming, desertification, drought, greenhouse effect, floods and many other problems are caused only because of deforestation. Ultimately, the next generation will be facing the consequences of deforestation.

4. What will happen if

(a) we go on cutting trees

(b) the habitat of an animal is disturbed

(c) the top layer of soil is exposed

Soln:

(a) If we go on cutting the trees

If we go on cutting the trees, the animals will lose their natural habitat as an essential part of their ecosystem are destroyed. This reduces the biodiversity of the affected areas. The temperature of the Earth also increases and gives way to global warming. Global warming, in turn, affects the water cycle. Hence, rainfall pattern changes leading to droughts and floods. Risks of soil erosion, global warming, desertification, greenhouse effect increases.

(b) If the habitat of an animal is disturbed

All the basic necessities for an animal, like food, water, shelter and protection is provided by the habitat in which the animal lives-in disturbing the habitat of the animal forces it to move to another place in search of food, water, shelter and protection. The animal, in due course, may get killed by other animals.

(C) If the top layer of the soil is removed

Removing the top layer of the soil gradually exposes the lower layers of the soil. The lower layers of the soil are hard and rocky in nature and are less fertile. This is because of the reduced quantity of humus. Soil erosion on a continued basis will turn it barren and infertile.

5. Answer in brief.

(a) Why should we conserve biodiversity?

(b) Protected forests are also not completely safe for wild animals. Why?

(c) Some tribals depend on the jungle. How?

(d) What are the causes and consequences of deforestation?

(e) What is Red Data Book?

(f) What do you understand by the term migration?

Soln:

(a) The number and variety of various life forms such as plants, animals and micro-organisms in the area are called Biodiversity. Both plants and animals have a mutual dependence on each other for their survival. As they are related to one another, destruction of one will automatically destroy the other. Hence, biodiversity has to be conserved in order to maintain nature’s balance.

(b) People who live near the forests depend on the resources of the forests in order to fulfil their day-to-day needs. Therefore, it is not safe for animals living in protected forests. The animals would be threatened by the presence of the human population. This results in the killing of wild animals and selling their products for huge sums of money.

(c) The forests provide food, fodder and other resources to the tribal people. It is inevitable for them to depend on forests and their resources for everyday needs.

(d) Causes of deforestation:

There are a lot of causes for deforestation. A few of them are listed below.

I. In order to accommodate the ever-expanding urban population, forest areas are often cleared and converted into lands for various uses.

II. For agricultural activities like crop cultivation and cattle grazing, forest lands are cleared.

III. Firewood is a major product from the forests and it is one of the main reasons for cutting the trees on a large scale.

Consequences of deforestation:

There are a lot of fatal consequences caused by deforestation. A few of them are listed below.

1. Soil erosion
2. Loss of Biodiversity
3. Floods
4. Droughts
5. Global warming as a result of climate change
6. Disruption of the water cycle

(e) Red data book is basically a sourcebook which has an international list of all plant and animal species which are endangered, that is, on the verge of extinction. The International Union for Conservation of Nature and Natural resources (IUCN) maintains the books and adds/ removes the names of the species by conducting a comprehensive survey.

(f) The movement of an organism or a group of organisms from its natural habitat to another place on a standard basis at a particular time of each and every year is known as migration. The organisms do so in order to avoid uninhabitable conditions of climate or for the process of breeding.

6. In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.

Soln:

No. Cutting trees in order to meet the ever-growing demands of the human population is not at all justified. There are a vast number of organisms like wild animals, insects, and birds living in the forests. The forests provide good quality air for both animals and humans. This is because of the process of plants respiration by which, they consume the harmful carbon dioxide and give out good quality Oxygen. Thus, keeping greenhouse gases and global warming under check. The roots of the flora of the forests help in preventing soil erosion. Natural Calamities such as floods and droughts could also be prevented by their presence. They help in increasing the soil’s fertility and conserving the biodiversity of the ecosystem.

Overutilization of forests and its resources by cutting a large number of trees in order to satisfy the demands of the ever-increasing human population, leading to many long-term problems like

• Soil erosion
• Greenhouse effect
• Global warming
• Floods
• Droughts

Besides the above-listed problems, the effects of large-scale deforestation will be leaving an everlasting mark on the face of human civilization. The balance of nature is disturbed by the destruction of trees. Hence, it is of utmost priority and importance to conserve forests.

7. How can you contribute to the maintenance of green wealth of your locality? Make a list of actions to be taken by you.

Soln:

I can take care of the green cover of my locality by growing plants in my locality. I shall motivate the people of my neighbourhood to plant more trees and take care of the existing trees by creating awareness about the importance of plant life in an ecosystem. In order to make this possible, I would initiate the proceedings and organize weekly events on the same. Creating awareness among the children and youth would be of top priority as they will easily understand the issues that we are facing. Planting new trees is as important as looking after the existing ones. So, my volunteers and I would water the plants and trees on a regular basis.

8. Explain how deforestation leads to reduced rainfall.

Soln:

Removal of trees and plant life from a particular area for the construction of industries, agriculture and other purposes is termed as Deforestation. Photosynthesis in plant life, takes place by the absorption of CO2 from the earth’s atmosphere. When the plant life is destroyed, the Carbon Dioxide levels in the atmosphere will increase drastically leading trap of heat radiation which causes global warming. This rise in temperature will affect the water cycle. Disturbance in the water cycle will lead to a chain of events and in the end, the rainfall pattern changes and results in droughts.

9. Find out about national parks in your state. Identify and show their location on the outline map of India.

Soln:

10. Why should paper be saved? Prepare a list of ways by which you can save paper.

Soln:

If one ton of clean white paper is to be produced, seventeen full-grown trees are cut down. Trees play a major role in maintaining a balance in nature. So, it is essential to save paper in order to protect the trees and avoid the impact of the loss of trees on the living organisms that depend on these trees.

Ways to save paper:

• Collection and recycling of used paper.
• Using both sides of a paper for writing.
• Spreading awareness about the importance of paper among school children and youth.
• Intelligent and proper use of paper.

11. Complete the word puzzle.

Down

1. Species on the verge of extinction.

2. A book carrying information about endangered species.

5. Consequences of deforestation.

Across

1. Species which have vanished.

3. Species found only in a particular habitat.

4. Variety of plants, animals and microorganisms found in an area.

Down

1. Endangered
2. Red Data Book
3. Deserts

Across

1. Extinct
2. Endemic
3. Biodiversity

Solutions of Worksheet, Class 8, Chapter 6

 1. Soln:

(a) A Chemical process in which a substance reacts with oxygen to give off heat is called combustion.

(b) When the clothes of a person catch fire, the person is covered with a blanket to extinguish the fire.

(c) The lowest temperature at which a substance catches fire is called its ignition temperature.

(d) The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.

(e) The substances which vapourise during burning give flame.

2. Soln:

1. True
2. False. Because, Magnesium is a combustible metal.
3. True
4. False-  Because the alorific value of coal is higher than that of wood.

3. Soln:

Column A	Column B Column C (zone)	Column C (colour)
(a) hottest part	(iii) the outer zone of complete combustion	(x) the blue of unburnt wax vapours
(b) moderately hot	(ii) middle zone of black partial combustion	(z) yellow
(c) least hot	(i) innermost zone	(y) black

4. Soln:

(a) A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

(b) Wood, paper, CNG are combustible substances.

(c) The lowest temperature at which a substance catches fire is called its Ignition temperature.

(d) Ignition temperature of petrol is lower than that of wood.

(e) The substances which have very low Ignition temperature and can easily catch fire with a flame are called Inflammable substances.

(f) The amount of heat energy produced on complete combustion of 1kg of a fuel is called its Calorific value.

Worksheet, Class 8, Chapter 6

1. Fill in the blanks in the following sentences.

(a) A ____________ process in which a substance reacts with __________ to give off heat is called combustion.

(b) When the clothes of a person catch __________, the person is covered with a __________ to extinguish fire.

(c) The __________ temperature at which a substance catches fire is called its __________ temperature.

(d) The substances which have very ________________ ignition temperature and can easily catch fire with a flame are called __________ substances.

(e) The substances which vapourise during __________, give flame.

2. Indicate whether the following statements are True or False. Also write the false statements in their correct form.

(a) Air is necessary for combustion.

(b) Magnesium is a non-combustible metal.

(c) Carbon dioxide is an excellent fire extinguisher.

(d) Calorific value of wood is higher than that of coal

3. Match the following for the flame of a candle.

Column A	Column B Column C (zone)	Column C (colour)
(a) hottest part	(i) innermost zone	(x) the blue of unburnt wax vapours
(b) moderately hot	(ii) the middle zone of black partial combustion	(y) black
(c) least hot	(iii) the outer zone of complete combustion	(z) yellow

4. 26. Fill in the blanks using the words given in the box.

(a) A chemical process in which a substance reacts with oxygen to give off heat is called __________.

(b) Wood, paper, CNG are __________ substances.

(c) The lowest temperature at which a substance catches fire is called its __________ temperature.

(d) Ignition temperature of __________ is lower than that of wood.

(e) The substances which have very low __________ temperature and can easily catch fire with a flame are called __________ substances.

(f) The amount of heat energy produced on complete combustion of 1kg of a fuel is called its __________