Oasis School Science and Technology 8 New

Oasis School Science and Technology - 8 97 UNIT 5 LIFE PROCESSES Estimated teaching periods Theory 12 Practical 3  Introduction to asexual reproduction in organisms  Introduction to sexual reproduction in organisms  Introduction to pollination  Introduction to fertilization  Vegetative propagation through stem, leaf and root  Structure of monocotyledonous and dicotyledonous seeds  Functions of parts of seeds  Dispersal of seeds  Effects of air, water and heat in the germination of seeds  Importance of germination of seeds The Sequence of Curriculum Issued by CDC Rudolf Jakob Camerarius is noted for his discovery of sexual reproduction in plants. He was born in the Roman empire on 12th February 1665 and died on 11th September 1721. He was a German botanist and physician. He experimented on Mulberry, castor oil plants and maize plant to discover that if male parts of the plant are removed then the fruits contain no seeds. Which meant no sexual reproduction. About the Scientist Rudolf Jakob Camerarius Key terms and terminologies 1. Life process : Various activities carried out by living organisms, which are necessary to maintain and continue life are called life processes. 2. Reproduction : The biological process by which living organisms produce their own kind by an asexual or sexual method is called reproduction. 3. Asexual reproduction : The method of reproduction which takes place from a single parent without the fusion of a male gamete and a female gamete is called asexual reproduction. 4. Fission : The method of asexual reproduction in which a parent organism divides into two or more daughter organisms is called fission.

98 Oasis School Science and Technology - 8 5. Binary fission : The fission in which a parent organism divides into two daughter organisms is called binary fission. 6. Multiple fission : The fission in which a parent organism divides into more than two daughter organisms at the same time is called multiple fission. 7. Budding : The method of asexual reproduction which takes place through the formation of a bud is called budding. 8. Sporulation : The method of asexual reproduction which takes place using spores is called sporulation. 9. Spores : Spores are the microscopic asexually reproductive bodies covered by a hard protective coat. 10. Regeneration : The ability of an individual to regain its lost parts is called regeneration. 11. Parthenogenesis : The process in which new offspring comes from unfertilized egg is called parthenogenesis 12. Vegetative propagation : The method of asexual reproduction in which new plants are produced by vegetative parts of plants like roots, stems or leaves is called vegetative propagation. 13. Cutting : Cutting is a common artificial method of vegetative propagation in which new plants are obtained by planting the piece of stem, root or leaf of plants in favourable conditions. 14. Layering : Layering is an artificial method of reproduction in which roots are developed on the stem while the stem is still attached to the parent plant. 15. Air layering : The process of growing roots on the target region of the stem by removing bark and then encasing them in a moisture-retaining medium, such as moss or cloth, wrapped by plastic is called air layering. 16. Grafting : The process in which a plant of superior quality is obtained by combining the root system of a plant with better survival rate and the shoot system of another required plant is called grafting. 17. Tissue culture : Tissue culture or micro-propagation is a modern technique of producing new plants from isolated plant cells or a small piece of plant tissue in a culture solution. 18. Sexual reproduction : The process in which reproduction takes place by the fusion of a male gamete and a female gamete is called sexual reproduction. 19. Complete flower : A flower that contains four floral whorls, viz. calyx, corolla, androecium and gynoecium is called a complete flower. 20. Pollination : The transfer of pollen grains from the anther to the stigma of a flower is called pollination.

Oasis School Science and Technology - 8 99 21. Self-pollination : The process of transfer of pollen grains from the anther to the stigma of the same flower or the stigma of another genetically identical flower of the same plant is called self-pollination. 22. Cross-pollination : The process of transfer of pollen grains from the anther of a flower of one plant to the stigma of a flower in other plants of the same species is called cross-pollination. 23. Fertilization : The process of fusion of a male gamete and a female gamete to form a zygote is called fertilization. 24. Seed : The reproductive unit of a plant which can germinate to produce a new plant in favourable conditions is called a seed. 25. Bisexual organisms : The organisms that can produce both male and female gametes from a single body is called bisexual organism or hermaphrodite. 26. Unisexual organisms : The organisms that can produce either male gamete or female gamete from a single body is called a unisexual organism. 27. Testis : The male gonad that produces sperm or male gametes by spermatogenesis is called the testis. 28. Ovary : The female gonad that produces ova or egg cells or female gametes by oogenesis is called the ovary. 29. Gametes : The haploid sex cells involved in sexual reproduction are called gametes. 30. Female gamete : The haploid female sex cell produced by the female sex organs is called the female gamete or ovum. 31. Radicle : The radicle is the embryonic root. 32. Plumule : The plumule is the embryonic shoot. 33. Hilum : The small scar on the seed coat is called the hilum. 34. Micropyle : The small opening near the hilum is called a micropyle. 35. Endospermic seeds : The seeds in which food is stored in the endosperm are called endospermic seeds. 36. Non-endospermic seeds : The seeds in which food is stored in cotyledons are called nonendospermic seeds. 37. Monocotyledonous seeds: The seeds having only one cotyledon are called monocotyledonous seeds. 38. Dicotyledonous seeds : The seeds having two cotyledons are called dicotyledonous seeds. 39. Germination : The process by which a seed embryo develops into a seedling is called germination. 40. Seed dispersal : The movement or transport of seeds away from the parent plant is called dispersal of seed.

100 Oasis School Science and Technology - 8 Introduction Living organisms perform various activities like respiration, nutrition, transportation of substances, excretion, movement, reproduction, etc. These activities are essential for survival of an organism and hence called life processes. Various activities carried out by living organisms, which are necessary to maintain and continue life are called life processes. Living organisms cannot survive in the absence of life precesses. Reproduction Living organisms cannot survive for ever. Each living being remains alive in this nature for a limited period of time and then it dies. So, living organisms produce their own kinds for continuity of the race of their species on the earth. The biological process in which living organisms produce their own kinds by asexual or sexual method is called reproduction. Reproduction can also be defined as the creation or production of new organisms from the pre-existing organisms of the same species. Living organisms reproduce by two methods to maintain the life of their species on the earth which are as follows: (i) Asexual reproduction (ii) Sexual reproduction Importance of Reproduction i. Reproduction helps to continue the generation of the species. ii. It protects species from being extinct. iii. It makes balance between the rate of birth and rate of death of the population. iv. It makes balance the biodiversity in an ecosystem. v. It is the basis of evolution of new organism. Asexual Reproduction Asexual reproduction is a common method of reproduction in lower plants and animals. In this method, a single organism is capable of reproduction. The method of reproduction which takes place from a single parent without the fusion of a male gamete and a female gamete is called asexual reproduction. In this process, no sex cells, i.e. gametes are involved. So, this method is called asexual reproduction. The new offspring produced by asexual method are genetically identical to their parents. Asexual reproduction involves the production of offspring from a single parent. Binary fission in amoeba, budding in hydra, regeneration in planaria, vegetative propagation in rose, etc. are some examples of asexual reproduction. Characteristics of asexual reproduction i. The process of asexual reproduction does not involve the production and fusion of gametes. ii. It does not required male and female. iii. This reproduction can be carried out from the parts of whole body. iv. The offspring obtained from asexual reproduction do not have variation. Methods of Asexual Reproduction The various methods of asexual reproduction are mentioned below:

Oasis School Science and Technology - 8 101 (a) Fission (b) Budding (c) Sporulation (d) Fragmentation or Regeneration (e) Vegetative propagation (f) Parthenogenesis (a) Fission The method of asexual reproduction in which a parent organism divides into two or more daughter organisms is called fission. It is common in unicellular organisms like Amoeba, Paramecium, Plasmodium, Bacteria, Euglena, etc. On the basis of the number of daughter organisms produced, fission is of two types: (i) Binary fission (ii) Multiple fission (i) Binary fission The fission in which a parent organism divides into two daughter organisms is called binary fission. In this method, the nucleus divides first into two daughter nuclei. This process is followed by the division of cytoplasm. Finally, the cell splits into two daughter cells. In this way, a parent organism divides into two daughter organisms. Binary fission occurs during favourable conditions of life. Some unicellular plants like Bacteria, Diatoms, etc. and animals like Euglena, Amoeba, Paramecium, Plasmodium, etc. reproduce by binary fission. Binary fission could be transverse or longitudinal. Longitudinal binary fission means the unicellular organism split vertically (from the longer side). Transverse binary fission means the unicellular organism split horizontally (from the shorter side). (ii) Multiple fission The fission in which a parent organism divides into more than two daughter organisms at the same time is called multiple fission. It occurs in unfavourable conditions. Many unicellular algae and some unicellular animals like Amoeba, Plasmodium, Chlamydomonas, etc. reproduce asexually by multiple fission during unfavourable conditions. Daughter nuclei Daughter Cyst Parent cell Fig: multiple fission in Plasmodium plasmodia Fig. Different types of binary fission

102 Oasis School Science and Technology - 8 Inmultiplefission, a cyst(i.e. a thickprotective layer)is formedaroundcellofunicellular organism in unfavourable condition. Inside the cyst, the nucleus divides repeatedly to produce many daughter nuclei. Later on, each nucleus is surrounded by cytoplasm and cell membrane. As a result, many daughter cells are formed inside the cyst. On the return of favourable conditions, the cyst breaks and small offspring are released. In this way, multiple fission takes place in unicellular organisms. Reasonable Facts Hydra cannot reproduce through binary fission. Hydra cannot reproduce through binary fission because it is observed in unicellular organisms only but hydra is multicellular. Activity 1 Make a modal to represent binary fission of amoeba. Differences between Binary fission and Multiple fission Binary fission Multiple fission 1. The process in which one parent body divides into only two daughter organisms is called binary fission. 1. The process in which one parent body divides into more than two daughter organisms is called multiple fission. 2. It is common in amoeba, bacteria, etc. 2. It is common in Plasmodium, Chlamydomonas, etc. (b) Budding It is a method of asexual reproduction in which a bud arises from the parent’s body which detaches and finally develops into a new organism. The method of asexual reproduction which takes place by the formation of a bud is called budding. This method is common in unicellular plants like yeast and multicellular animals like hydra, taenia, coral and jelly fish. In yeast, a bulb-like outgrowth (i.e. bud) is formed on one side of the cell. The nucleus divides and one daughter nucleus passes into the bud. The bud grows and finally gets detached from the parent cell which grows in size and becomes a new yeast. Fact File The word fission is derived from Latin word ‘fissio’ means to split. Fig: budding in yeast Bud Bud Fig: budding in hydra Bud grows Bud separates

Oasis School Science and Technology - 8 103 (c) Sporulation In this method, the parent plant produces a large number of tiny spores which can produce new plants. The method of asexual reproduction which takes place by means of spores is called sporulation. This method is common in Mucor, Moss, Marchantia, Chlamydomonas, etc. In mucor, small knob-like structures called sporangia (singular–sporangium) develop at the top of hyphae. Numerous spores are produced inside the sporangium. by the process of sporogenesis. Spores are the microscopic asexually reproductive bodies covered by a hard protective coat. Spores germinate into new organisms under favourable conditions. At maturity, sporangia burst open to release spores, which grow into new organisms on favourable condition. Activity 2 To observe sporulation in mucor • Take a slice of bread and keep it in a moist and warm place for 4-5 days. • After 4-5 days, you can see a white cottony mass of mucor. • Keep the slice of bread in the sunlight for 2-3 days. • Observe the surface of mucor under the hand lens and compound microscope. • Draw the labelled figures and write a few comments on the basis of your observation. Fig: growth of mucor on bread (d) Fragmentation or Regeneration Fragmentation is the method of asexual reproduction in which a multicellular organism breaks into two or more fragments and each fragment develops into a new complete organism. The ability of an individual fragment of an organism to replace its lost parts is called regeneration. It can also be defined as the process of getting back a complete organism from its body parts. Fig: (a) Regeneration in Planaria (b) Fragmentation in Spirogyra sporangium mycelium (a) (b) columella spores sporangial wall Fig: sporulation in mucor

104 Oasis School Science and Technology - 8 In fragmentation, a parent multicellular organism breaks down naturally to produce two or more pieces. After a certain time, each piece of the organism regenerates itself to form a complete organism by growing all missing parts. Filamentous algae like spirogyra, marchantia, fern, lichen and animals like hydra, planaria, tapeworm, starfish, earthworm etc. reproduce asexually by this method. Please note that the term ‘fragmentation’ is generally used for plants and the term ‘regeneration’ is used for animals. Reasonable Facts The asexual reproduction that occurs in planaria is called regeneration. When planaria breaks into two or more parts then each part grows into a new complete planaria. So, asexual reproduction that occurs in planaria is called regeneration. (e) Parthenogenesis Sometimes a female snake that has never met a male partner can hatch new snakes from its egg. The process in which new offspring comes from unfertilized egg is called parthenogenesis. It is common in ants and grasshoppers. Plants such as apple, cucumber, jack fruit etc. also show parthenogenesis. (f) Vegetative Propagation Vegetative propagation is the method of asexual reproduction common in some higher plants. In this method, a bud grows on the vegetative part of plant like a stem, root or leaf and develops into a new plant. On maturity, the new plant detaches itself from the parent plant and lives as an independent plant. Thus, vegetative propagation is the method of asexual reproduction in which new plants are produced by vegetative parts of plants like root, stem or leaf. It could be artificail or natural. Reasonable Facts Rose plants are propagated through cutting. Rose plants are propagated through cutting which is an artificial vegetative propagation because rose plants do not have viable seeds. A. Natural vegetative propagation (i) Vegetative Propagation by Roots Some flowering plants like sweet potato, dahlia, mint, etc. reproduce asexually by means of roots. Roots of those plants contain adventitious buds. When such roots are planted in the soil, new plants are produced. Fact File Vegetative propagation does not happen from any random part of the plant. Fig: vegetative propagation by roots (a) Dahlia (b) Sweet potato

Oasis School Science and Technology - 8 105 (ii) Vegetative Propagation by Stem At maturity, the stem of certain plants develops buds on it. The part of stem having buds serves as an organ for vegetative propagation. When the stem falls on the ground, it propagates new plants on favourable condition. For example, bulb of onion, stem of rose, tuber of potato, etc. reproduce asexually by means of stem. (a) Tuber of potato (b) Bulb of onion (c) Aerial stem of sugarcane main root eye scale leaf root New plant Node Intermode Node disc bud scale leaf Fig: vegetative propagation by stem Reasonable Facts Though potato is a seed-bearing plant, it reproduces through vegetative propagation, why? Though potato is a seed-bearing plant, it reproduces asexually through vegetative propagation because a potato does not produce viable seeds. Activity 3 To observe vegetative propagation by stem in sugarcane • Bring a mature sugarcane and cut it into small pieces. • Observe the buds in the nodes of the sugarcane. • Plant these pieces in the soil and supply water regularly. • Observe after 2-3 weeks. • Prepare a report with the labelled figures and submit to your science teacher. Reasonable Facts Vegetative propagation is beneficial for farmers. Vegetative propagation is beneficial for farmers because of the following reasons: i. Gardeners, farmers and botanists can grow a large number of plants by this method. ii. The plants which do not produce viable seeds like rose, sugarcane, potato, etc. can easily be propagated by this method.

106 Oasis School Science and Technology - 8 a. Vegetative propagation by underground stem Some plants like onion, tulip, daffodil, arum, colocasia, gladiolus, ginger, potato, etc. reproduce asexually using an underground stem. Stems of these plants contain buds on them. Each bud of the stem can grow into a new plant in favourable conditions. b. Vegetative propagation by sub-aerial stem Some plants like water hyacinth, water lettuce, etc. reproduce by offset. Strawberry, raspberry, buttercup, blackberry, gooseberry, bamboo, pineapple, mint, chrysanthemum, banana, etc. reproduce asexually using a sub-aerial stem. (iii) Vegetative Propagation by Leaf Leaves of some plants like Bryophyllum, Begonia, etc. produce adventitious buds from the notch, at the end of leaf blade, lamina and veins. Those buds develop into small plantlets when the leaf falls on the moist soil. These plantlets get separated from the leaf and grow into new plants. Leaf of Bryophyllum New plantlets New plantlet Leaf of Begonia Fig: vegetative propagation by leaf (iv) Vegetative propagation by bulbil The group of buds at the apex of branches or stem is called bulbil. Certain plants can grow new plants from this structure. B. Artificial vegetative propagation Besides natural methods of vegetative propagation, artificial methods of plant reproduction are also common among farmers, gardeners, horticulturists etc. Various methods like cutting, grafting, layering, tissue culture, etc. are used to reproduce plants asexually in gardens and nurseries. a. Cutting Cutting is a common artificial method of vegetative propagation in which new plants are obtained by planting the piece of stem, root or leaf of plants in favourable conditions. Each cutting piece should have at least two buds for propagation.

Oasis School Science and Technology - 8 107 Fig: asexual reproduction by cutting Some plants like sugarcane, rose, potato, pear, raspberry, black berry, etc. are propagated by stem cutting. Lemon, tamarind, etc. are propagated by root cutting and Begonia, Bryophyllum, African violets, etc. are propagated asexually by leaf cutting. b. Layering Layering is an artificial method of reproduction in which roots are developed on the stem while the stem is still attached to the parent plant. Layering is commonly used in jasmine, magnolia, strawberry, raspberry, etc. Many plantlets can be produced in a short period by this method. Layering is induced artificially by bending the branch to the ground and covering it with moist soil. The apical part of the stem produces leaves whereas the underground part produces roots. Later the layered branch is separated from the parent plant. c. Gootee (Air layering) Air layering is the most popular method of artificial vegetative propagation. In this method, the target region of the stem is wounded, or a strip of bark is removed and then encased in a moisture-retaining medium, such as moss or cloth, which is further surrounded by a moisture barrier such as a plastic film. Rooting hormone, i.e., I.B.A. hormone (Indole-3 butyric acid) is often applied to encourage the growth of roots. The wounded portion develops roots within 4-8 weeks. Then, the portion is separated from the parent plant and planted. Example: litchi, mango, guava, orange d. Grafting In this method, a plant of superior quality is obtained by combining the root system of a plant and shoot system of another plant. The plant whose root system is taken is Fig: air layering

108 Oasis School Science and Technology - 8 called stock and whose shoot system is taken is called the scion. This technique is used in mango, rose, lemon, apple, peach, plum, etc. In grafting, the ends of a scion and stock to be grafted are cut obliquely and placed face to face in such a way that the cambia of both plants are in close contact. Then the scion and stock are bound firmly with tape (cloth) and covered with wax. After a few weeks, both the scion and stock combine firmly, resulting in a new plant. e. Tissue culture Tissue culture or micropropagation is a modern technique of producing new plants from isolated plant cells or a small piece of plant tissue in a culture solution. The culture solution or medium is very important in tissue culture. The solution contains a special mixture of salts, vitamins and plant hormones. Ornamental plants like orchids, dahlia etc. are propagated artificially by this technique. In tissue culture, a few cells (or tissues) oftheplantto bepropagated are taken and kept in a culture solution under sterile conditions. In this solution, a shapeless lump, i.e., callus is produced by the rapid division of the plant cells. Then the callus is transferred into another culture solution containing suitable plant hormones, which stimulates the callus to develop roots. The callus with roots is again transferred into another culture solution having different hormones that stimulate the development of shoots. The callus has roots and shoots which can be separated into many tiny plantlets. The plantlets thus produced are transplanted into soil or pots to get natural plants. Advantages of artificial vegetative propagation i. It is used to produce multiple plants at a time. ii. The plants grown from this technique bears flower and fruit faster. iii. It helps to improve generation of organisms. iv. It is used for propagation of the plants which do not have viable seeds. Significance of Asexual Reproduction i. Asexual reproduction produces new individuals with exactly identical to the parent. ii. It is a faster, easier and cheaper method of reproduction. iii. The plants produced by vegetative propagation bear flowers and fruits earlier than those produced from seeds. iv. The plants which do not produce viable seeds (like sugarcane, rose, potato, banana, bamboo, etc.) can easily be propagated by asexual reproduction. Fig: tissue culture

Oasis School Science and Technology - 8 109 Sexual Reproduction Sexual reproduction is a complex process of reproduction in which both sexes, the male and female, are involved. Most animals and higher plants reproduce by sexual reproduction. The process in which reproduction takes place by the fusion of a male gamete and a female gamete is called sexual reproduction. In this method, a male gamete and a female gamete unite to form a zygote which finally develops into a new organism. Sexual Reproduction in Flowering Plants In flowering plants, sexual reproduction is the most common method of reproduction. In higher plants, floweris the sexually reproductive organ. A complete flower contains four floral whorls, viz. calyx, corolla, androecium and gynoecium. At maturity, anthers begin to dry and burst open to release pollen grains. The pollen grains are transferred to the stigma of a flower by many external agents like insects, wind, birds, water, animals, etc. This process is called pollination. Pollination is the transfer of pollen grains from the anther to the stigma of a flower. In flowering plants, pollination is followed by fertilization. Fig: structure of a flower stigma style ovary receptacle pistil pedicel sepal petal filament anther After fertilization, the ovule develops into seed and ovary into the fruit. The seed is a reproductive unit of a plant which can germinate to produce a new plant on favourable condition. In this way, flowering plants reproduce sexually by forming seeds through flowers. Reasonable Facts Sexual reproduction improves adaptation capabilities of organisms. Sexual reproduction improves adaptation capabilities of organisms because male and female contribute different physical traits to form zygote. It helps offspring to gain better physical abilities. Fact File Unisexual flowers have either androecium or gynoecium only.

110 Oasis School Science and Technology - 8 Activity 4 To observe various parts of flowers • Visit a garden and collect different types of flowers. • Separate the sepals, petals, stamens and pistils of each flower. • Draw their figures and label them. • Also, write down the similarities and differences among them. Pollination At maturity, anthers begin to dry and burst open to release pollen grains. The pollen grains are transferred to the stigma of a flower by many external agents like insects, wind, birds, water, animals, etc. Pollination is the process of transfer of pollen grains from the anther to the stigma of a flower. It is of two types: self-pollination and cross-pollination. Self-pollination is the process of transfer of pollen grains from the anther to the stigma of the same flower or to the stigma of another genetically identical flower of the same plant. This process is common in bisexual flowers, e.g. China rose, pea, etc. Fig.16.34 Types of pollination Self-pollination Cross-pollination Self-pollination Advantages of self-pollination i. As a result of self-pollination the offspring carry the parental characters. ii. Self-pollination helps to obtain pure bred organisms. iii. It is an easy way of pollination. Disadvantages of self-pollination i. As a result of self-pollination the offspring do not carry the new characters. So, there is no evolution in the coming generation. ii. The continuous self-pollination declines the power of reproduction in coming generation. iii. We can not eliminate the bad characteristics of the parents in the coming generation. Cross-pollination is the process of transfer of pollen grains from anther of a flower of one plant to the stigma of a flower in other plants of the same species. This process is common

Oasis School Science and Technology - 8 111 in both unisexual and bisexual flowers. External agents of pollination are essential for cross-pollination. In flowering plants, pollination is followed by fertilization. Advantages of cross-pollination i. As a result of cross-pollination the offspring of better characters are produced. ii. Offspring of cross-pollination are better suited in the changing environment. iii. It helps in evolution of the organisms. Disadvantages of cross-pollination i. Cross-pollination depends upon external agents. In absence of external agents, it does not occur. ii. As a result of cross-pollination, the offspring with unwanted characters may produced. iii. As a result of cross-pollination, the beneficial characteristics of the offspring may disappear. iv. It does not make sure of seed production. Differences between Self-pollination and Cross-pollination Self-pollination Cross-pollination 1. It is the process of transfer of pollen grains from the anther to the stigma of the same flower or to the stigma of another genetically identical flower of the same plant. 1. It is the process of transfer of pollen grains from anther of a flower of one plant to the stigma of a flower of another plant of the same species. 2. External agent of pollination are not required. 2. External agents of pollination like insects, wind, water, etc. are required. 3. It does not help in variation. 3. It helps in variation. Fertilization Fertilization is the process of fusion of a male gamete and a female gamete to form a zygote. In flowering plants, pollen grains absorb secretions from the stigma and undergo germination after pollination. The germinating pollen grain produces a pollen tube which grows down towards style and finally reaches the ovule in the ovary. The fertilization in flowering plants involves the fusion of two male gametes separately. One male gamete fuses with the egg cell (ovum) and forms zygote. It is first fertilization. Similarly, another male gamete fuses with the secondary nucleus and forms endosperm nucleus. Therefore, the fertilization in flowering plants is called double fertilization. After fertilization, the zygote divides and forms embryo whereas the endosperm nucleus develops into endosperm of the seed. An embryo is the baby plant in the very early stage of its development before coming out of its seed whereas the endosperm is the food storage tissue of the seed. The embryo and endosperm together make a seed. After fertilization, the ovule forms seed and ovary

112 Oasis School Science and Technology - 8 forms the fruit. A seed is a reproductive unit of a plant which can germinate to produce a new plant on favourable condition. Fig: life cycle of a flowering plant Germinated pollen grain Anther at tip of stamen Pollen tube Ovary (base or carpel) Embryo sac Egg Sperm Germinating seed Seedling Mature plant with flowers Seed Seed (develops from ovule) Simple fruit (develops from ovary) Embryo Zygote Ovule Reasonable Facts The reproduction that occurs in flowering plants is called sexual reproduction. Reproduction in flowering plants takes place by the fusion of a male gamete and a female gamete. So, the reproduction that occurs in flowering plants is called sexual reproduction. Differences between Pollination and Fertilization Pollination Fertilization 1. The process of transfer of pollen grains from anther to the stigma of a flower is called pollination. 1. The process of formation of a zygote by the fusion of male gamete and female gamete is called fertilization. 2. This process is found only in flowering plants. 2. This process is common in both flowering plants and animals that reproduce by sexual method. Activity 5 • Visit a crop field and uproot a mustard plant or any other flowering plant. • Observe its root, stem, leaves, flowers and fruits. • Draw a neat diagram and label the main parts.

Oasis School Science and Technology - 8 113 Sexual Reproduction in Animals Sexual reproduction is the only method of reproduction in vertebrate animals but it is also found in lower group of invertebrates like paramecium, flatworms,roundworms, arthropods, molluscs, etc. Among them, some animals are unisexual and some are bisexual. Bisexual animals can produce both male and female gametes whereas unisexual animals can produce either male gamete or female gamete. The process by which animals produce gametes is known as gametogenesis. In animals, gonads are the primary sex organs which produce gametes or sex cells. Testis is the male gonad that produces sperms or male gametes by spermatogenesis. Similarly, ovary is the female gonad that produces ova or egg cells or female gametes by oogenesis. After the formation of gametes, fusion of a male gamete and a female gamete takes place which results in the formation of a zygote. The zygote divides mitotically and forms an embryo which finally develops into a young animal. The duration in which an organism develops from a zygote into a young living organism is called embryonic period or pregnancy period. Gametes Sexual reproduction takes place by the fusion of two special type of haploid cells called sex cells. These sex cells are called gametes. Thus the haploid sex cells involved in sexual reproduction are called gametes. Sex cells or gametes are of two types, viz. male gamete and female gamete. The male gamete is a haploid male sex cell produced by testis/anther. The male gamete of an animal is called sperm. It is motile and smaller in size. The female gamete or ovum is the haploid female sex cell produced by female sex organ, i.e. ovary. It is also called egg. It is non-motile and larger in size. On favourable condition, a male gamete and a female gamete fuse together and form a diploid zygote. (a) Sperms (male gametes) (b) Eggs (female gametes) Fig: gametes or sex cells Fig: gametes and zygote Haploid sperm Diploid zygote Haploid egg Fact File The process of formation of gamete is called gametogenesis.

114 Oasis School Science and Technology - 8 Internal fertilization The fusion of male and female gamete inside the fallopian tube of the female is called internal fertilization. It is observed in reptiles, aves and mammals. External fertilization The fusion of male and female gamete outside the female body, usually in water is called external fertilization. it is observed in pisces and amphibians. Reasonable Facts Sperms have tail. Sperms have tails so that they can use it to swim towards egg. Fig: external fertilization in amphibia Fig: Internal fertilization in aves Unisexual and Bisexual Organisms Sexes are separate in most of the developed animals. The organism having only one kind of reproductive system (either male or female) is called unisexual organism. Such organism has one sex only. Human beings, birds, mammals, reptiles, frogs, fishes, etc. are some examples of unisexual animals. Unisexual organisms produce only one kind of gametes, i.e. male gamete or female gamete. Some animals possess both male and female reproductive organs in the same body. The organism having both male and female reproductive systems (male and female) in its body is called bisexual or hermaphrodite animal. Hermaphrodite organism can produce both male and female gametes. Some animals like tapeworm, liver fluke, earthworm, hydra, leech, etc. and most of the flowering plants are bisexual organisms. Reasonable Facts Earthworm is called a bisexual organism. Earthworm has both male and female reproductive organs in its body. So, earthworm is called a bisexual organism.

Oasis School Science and Technology - 8 115 Reasonable Facts The fertilization that occurs in fish and frog is called external fertilization. The fusion of a male gamete and a female gamete in fish and frog takes place outside the body of female i.e. in water. So, fertilization that occurs in fish and frog is called external fertilization. Significance of Sexual Reproduction i. Sexual reproduction gives continuity to the generations. ii. It brings out genetic variation in organisms which leads to evolution. iii. Increase in genetic variation in a species results in better survival of that species in the changing environment. Differences between Asexual Reproduction and Sexual Reproduction S.N. Asexual Reproduction S.N. Sexual Reproduction 1. It takes place without the fusion of a male gamete and a female gamete. 1. It takes place by the fusion of a male gamete and a female gamete. 2. Only single parent is involved in asexual reproduction. 2. Both male and female organisms are involved in sexual reproduction. 3. This method is common in primitive plants and animals. 3. This method is common in developed plants and animals. Seed A seed is a ripened ovule of a flowering plant. It is a small embryonic plant enclosed in a covering called the seed coat. A seed is the product of a mature ovule of gymnosperms and angiosperms. Flowering plants produce different types of seed. Seeds of some plants are very small whereas seeds of some plants are large. Seeds of mango, coconut, peach, pumpkin, bean, etc. are examples of large seeds. The seeds of one plant differ from those of other plants. Fig: Some seeds Avocado seed Wheat seeds Maize seeds Pea seeds Fact File Palm tree produces the largest seed in the world.

116 Oasis School Science and Technology - 8 Activity 6 • Collect some seeds of pea, soyabean, gram, maize, wheat, etc. and keep them in water in separate beakers for one day. Those seeds absorb water and become larger. • Observe their size and draw their diagrams. • Gently remove their seed coat and observe their internal parts. • Draw the neat figures showing their internal structure. Structure of a Seed Various plants have various types of seeds. Their shapes and sizes are different, however their basic structure is similar. A typical seed has three main parts–embryo, a supply of nutrients for the embryo (endosperm) and a seed coat. i. Embryo The embryo is an immature plant from which a new plant will grow under favourable conditions. A seed consists of cotyledons, radicle and plumule. It has one cotyledon or seed leaf in monocots, two cotyledons in dicots and one or more in gymnosperms. ii. Endosperm In monocots, the storage tissue is called endosperm but the cotyledons themselves serve as storage tissue in dicots. The radicle is the embryonic root. It is the first portion of the embryo to break through the seed coat. It develops root hairs that absorb water and attach the embryo to particles of soil. The plumule is the embryonic shoot. The embryonic stem above the part of attachment of cotyledons is called epicotyl and below the point of attachment is called hypocotyl. After germination, plumule develops into stem and leaves. iii. Seed coat Seed coat is a hard and tough structure derived from the integument (outer layer) of ovule. This protective covering is called testa. In flowering plants, a thin and membranous covering is found inside the testa which is known as tegmen. The seed coat in a mature seed can be paper-thin layer (e.g. peanut) or thick and hard (e.g. coconut, walnut, peach, etc.). The seed coat helps protect the embryo from mechanical injury and from drying out. In addition to these three basic parts, some seeds have additional projections from Testa Testa Tegmen Plumule Epicotyl Hypocotyl Cotyledon Plumule Radicle (a) Structure of a maize seed (b) Structure of a gram seed Fig: Structure of seed

Oasis School Science and Technology - 8 117 the seed coat. Those projections serve to aid the absorption of water when seed is about to germinate. There is a small scar on the seed coat called the hilum. It is found where the seed was attached to the ovary wall. There is a small opening near the hilum which is called micropyle. Water enters inside the seed through this opening. So seeds are enlarged when soaked in water or sown on the soil. It helps in the germination of seed. Differences between Radicle and Plumule Radicle Plumule 1. The radicle is the embryonic root 1. The plumule is the embryonic shoot. 2. It grows towards the soil. 2. It grows away from the soil. Types of Seeds There are two types of seeds on the basis of presence of food storage tissue, viz. endospermic seeds and non-endospermic seeds. a. Endospermic seeds The seeds in which food is stored in endosperm are called endospermic seeds. All monocot seeds are endospermic seeds. Examples: Seeds of maize, wheat, rice, bajra, etc. Castor seed is a dicot seed which contains endosperm. b. Non-endospermic seeds The seeds in which food is stored in cotyledons are also called non-endospermic seeds. All dicot seeds are non-endospermic seeds except castor seeds. Examples: seeds of pea, soyabean, gram, orange, apple, etc. On the basis of number of cotyledons, there are two types of seeds, viz. monocot seeds and dicot seeds. a. Monocotyledonous seeds [mono–one, cotyledon–seed leaf] The seeds having only one cotyledon are called monocotyledonous seeds. In monocot seeds, endosperm occupies the major portion of the seed. Maize seed is an example of a monocot seed. The broader part of maize seed contains endosperm which consists of yellow or white reserve food material. The narrower part of the seed contains cotyledon. In the cotyledon, a small embryo is present. Plumule is present on the broader part of the seed whereas radicle is present on the opposite side of the plumule. Endosperm and embryo are separated by a thin membrane in the seed of maize. Seeds of wheat, barley, paddy, etc. are also the examples of endospermic monocot seeds. Rice Wheat Maize Fig: some monocotyledonous seeds

118 Oasis School Science and Technology - 8 Reasonable Facts Seed of paddy is called monocotyledon. Seed of paddy is called monocotyledon because a single grain of paddy has only one cotyledon. b. Dicotyledonous seeds [di - two, cotyledon - seed leaf] The seeds having two cotyledons are called dicotyledonous seeds. Seeds of pea, mango, bean, gram, apple, mustard, orange, etc. are some examples of dicotyledonous seeds. Endosperm is absent in dicot seeds. The cotyledons themselves serve as storage tissue in dicots. Gram seeds Pumpkin seeds Mango seed Fig: some dicotyledonous seeds Differences between Monocotyledonous seed and Dicotyledonous seed S.N. Monocotyledonous seed S.N. Dicotyledonous seed 1. A monocotyledonous seed contains only one cotyledon. 1. A dicotyledonous seed contains two cotyledons. 2. Endosperm is present. 2. Endosperm is absent. 3. Plumule is very small. 3. Plumule is large. 4. Embryo is small. 4. Embryo is large. 5. Micropyle and hilum are microscopic. 5. Micropyle and hilum are distinct. Functions of Seed The major functions of seed are as follows: i. To produce new plants ii. To store food materials Seeds serve several functions for the plants. Major functions among these are nourishment of the embryo, dispersal to a new location and dormancy during unfavourable condition. Seeds are the means of sexual reproduction in flowering plants. Seeds protect and nourish the embryo or baby plant. Seed germination Seed germination is a process by which a seed embryo develops into a seedling and subsequently a plant. It is the resumption of the growth of a seed embryo after the period

Oasis School Science and Technology - 8 119 of dormancy, i.e. resting period. Germination involves the reactivation of the metabolic pathways that lead to growth and the emergence of the radicle and plumule in it. (a) Bean seed germination (b) Maize seed germination Fig: germination Germination does not take place unless the seed has been transported to a favourable condition. The primary conditions of a favourable environment are adequate water, oxygen and suitable temperature. Different species of plants germinate best in different temperatures, however extremely hot or cold temperatures are not suitable for germination. Some seeds also require adequate exposure to light before germination. Thus, water, air and suitable temperature are necessary conditions for germination of a seed. Activity 7 • Take three seeds each of maize, bean, pea, gram, wheat, etc. • Keep them in the moist soil and allow them to germinate. • Observe the little plantlet carefully and identify the radical and plumule. Factors affecting germination of seed Germination of a seed depends upon water, air, temperature and light. a. Water A dry seed does not germinate because respiration and other metabolic activities does not occur inside the seed. When the seed absorbs sufficient water from micropyle, enzymes are activated which starts chain bio-chemical reactions. It initiates the germination process. b. Air The air contains oxygen. When a seed absorbs oxygen, respiration occurs in it. The energy produced from respiration increases metabolic activities in the embryo. As a result germination occurs. c. Temperature Seeds are dormant at lower temperatures. If it gains temperature from 16 to 25 ⁰C, embryo becomes active for germination.

120 Oasis School Science and Technology - 8 d. Light The sunlight helps to develop shoot from plumule and root from radicle. Importance of seed germination i. Seed germination helps in the continuity of generation. ii. The germination of seeds helps in the production of flower, fruits and seeds. iii. Germinated seeds have more nutrients. Which is good for health. iv. Germination of seeds helps in the growth of plants and increase the biodiversity. Activity 8 • Take three bean seeds and tie them on a glass slide. • Keep the slide in a beaker containing water in such a way that one seed is completely immersed in water, the middle one is half–immersed in water and upper most one is in air. • After 3-4 days, observe the seeds. You can see the germination of only the middle seed as it gets all three conditions air, water and temperature. • Write down the conclusion of this experiement. Seed in air Water Seed inside water Seed partially in water Reasonable Facts Germination of seed does not occur in dry soil. Water is necessary for germination of a seed. But in dry soil there will be no water. So, germination of seed does not occur in dry soil. Reasonable Facts The seed kept in a closed container does not germinate. Air is necessary for germination of seed. But in a closed container, there will be no sufficient air. So, seed kept in closed container does not germinate. Reasonable Facts Immatured seed does not germinate though it gets suitable condition. Immatured seed does not germinate though it gets suitable condition because it has under developed embryo. Dispersal of seed Seed dispersal is the movement or transport of seeds away from the parent plant. Seeds are dispersed by various methods which are as follows:

Oasis School Science and Technology - 8 121 i. By wind Seeds of some plants are very light having hairy or fluffy parachute-like structure. Such type of seeds are dispersed by wind. Seeds of simal, grass, cotton, dandelion, etc. are dispersed by wind. Fig: dispersal of seeds by wind (a) Seeds of dandelion (b) Seeds of cotton ii. By water Seeds of some plants like coconut, lotus, water lily, betel nut, etc. are dispersed by water. Seeds of these plants do not decay in water for a long time and germinate in favourable condition. (a) Seeds of coconut (b) Seeds of betel (c) Seeds of water lily Fig: dispersal of seeds by water iii. By explosion of fruits Fruits of some plants explode themselves after drying and disperse seeds in their surroundings with a jerk. Seeds of sesame, pea, myrtle (Tiuri), linseed (Aalas), etc. disperse by the explosion of fruits. Fig: dispersal of seeds by explosion of fruit (a) Pea (b) Sesame (c) Myrtle (d) Linseed

122 Oasis School Science and Technology - 8 iv. By animals Seeds of some plants have hooks or sticky structures on their surfaces. These structures attach to the fur of mammals or clothes of human beings and get dispersed. Birds and other animals eat the fleshy fruits and discard the seeds. Similarly, birds and other animals eat fruits with seeds but the seeds are not digested and pass out with their droppings far away from the parent plant. Seeds of tomato, guava, myrtle, etc. are dispersed by animals. v. By human beings Now-a-days, human beings transport fruits and seeds of different plants from one place to another and help in seed dispersal. Seeds of most fruits, vegetables, crops, flowers, etc. are dispersed by human beings. vi. Dispersal by gravity The ripe fruits are broken from branches as they are pulled by gravity. They decay in ground and germinate later. Usually hard fruits such as apple and mango disperse in this way. Reasonable Facts Different types of plants are found on the banks of rivers. On the banks of rivers, fertile soil, sufficient amount of water and appropriate climate is available for the development of plants. Similarly, different types of seeds of different plants are carried by river water and they get collected on the bank of river. So, different types of plants are found on the banks of rivers. Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. Potato has some eyes in it. If it is put in a closed room for a week, eyes will change into a new shoot. We can plant it in the fields. What type of asexual reproduction is it? How is it beneficial for farmers? Potatoes have some eyes, which can grow into the shoot, that can be planted to grow new plants. This type of asexual reproduction is vegetative reproduction by stem. It is beneficial for farmers because: i. It grows new plants faster. ii. It helps to grow plants that have poor-quality of seeds. iii. It helps to save the qualities of parent plants iv. A large number of new plants can be grown at once. Fig: some seeds have hooks to fix in animal fur Fact File Dispersal of seed is mechanism to travel and find better place to germinate.

Oasis School Science and Technology - 8 123 2. Wild banana has seeds in them but cultivated banana are seedless. How do farmers grow new banana plants then? What type of asexual reproduction is it? Most cultivated bananas are seedless. Farmers cannot grow new banana plants from seeds. Farmers grow new banana plants from thick, underground rhizomes. Little plants called pups grow from rhizome. It is called vegetative propagation by stem. 3. Cross-pollination increases the survival rate of organisms. The process in which the pollen grains transfer from the anther of one breed to the gynoecium of another breed of the plant is called cross-pollination. When pollen grain and eggs of different breeds fertilize to form the zygote, many new and better genes are collected in the offspring. Better genes help to remove weak characteristics and diseases. It helps to improve disease resistance, flowering, fruiting, weather resistance, etc. 4. What is fertilization? Frogs have external fertilization. What does it mean? The process in which a male gamete fuses with a female gamete to produce a zygote is called fertilization. Frogs have external fertilization. It means that the zygote is not formed inside the body of the frog. The fertilization occurs outside the body of frogs. It usually occurs in water. The female frog lays eggs that keep floating in the water. The male frogs also release male gamete in the water in the pond. The male gametes and female gametes meet and fuse in water. The zygote forms in the water which is outside the body of the frog. So frogs have external fertilization. 5. Differentiate between binary fission and multiple fission. The differences between binary fission and multiple fission are: SN Binary fission SN Multiple fission 1 The fission in which a parent organism divides into two daughter organisms is called binary fission. 1 The fission in which a parent organism divides into more than two daughter organisms at the same time is called multiple fission. 2 Binary fission occurs mostly when the unicellular mother organism is healthy. 2 Multiple fission occurs mostly when the unicellular mother organism is sick or starved. 6. Some seeds have hooks. Why do they have those hooks? How does it increase their survival rate? Some seeds have hooks. These hooks help them in dispersal. They can fix themselves in the animal fur and travel far away from the parent plant. They drop somewhere else and germinate if they can find moisture and minerals. If all of the seeds germinate around the parent plant, they would not get sufficient minerals and water. They could die. So growing far away from the parent plant helps them to survive. A different environment can also bring good variations in them. 7. Elle saw that grams were stored in a glass bottle in her kitchen. She asked her mom why are there no seedlings. What her mom should tell her? What should she do if she wants to grow seedlings from them? Elle saw that a few grams were stored in a glass bottle in her kitchen. Those seeds did not germinate for many days. She asked her mom about it. Her mom told her that the seeds could not germinate because it was stored in an airtight bottle. It could not receive

124 Oasis School Science and Technology - 8 the required moisture, oxygen and suitable temperature. If she wants to grow seedlings from these grams, she should put seeds in the soil and water them. 8. A new rose plant is grown by planting a piece of its stem in the soil. What type of asexual reproduction is it? Give three reasons why such type of reproduction is more beneficial. A new rose plant is grown by planting a piece of its stem in the soil. This type of reproduction is called vegetative propagation by stem. This type of reproduction is more beneficial than other types of reproduction due to the following reasons: i. Gardeners, farmers and botanists can grow a large number of plants by this method. ii. The plants which do not produce viable seeds like a rose, sugarcane, potato, etc. can easily be produced by this method. iii. The plants produced by this method bear flowers and fruits earlier than those produced from seeds. Exercises 1. Choose the best answer from the given alternatives. a. By which means of asexual reproduction do amoeba reproduce? i. budding ii. fission iii. sporulation iv. fragmentation b. What is the type of reproduction in which a zygote is formed? i. amitosis ii. fission iii. asexual reproduction iv. sexual reproduction c. What is the process of asexual reproduction in which a parent cell divides into two identical cells? i. budding ii. fission iii. binary fission iv. multiple fission d. What is the objective of a parachute-like tiny fur in some seeds? i. cross pollination ii. land slowly in the ground iii. travel long distances iv. they like flying e. When does amoeba undergo multiple fission? i. if it has collected enough nutrients to do so ii. if it has a suitable, healthy environment to do so iii. if it is sick or starving in dirty water iv. if the amoeba is a healthy and large adult 2. Define the following terms with required examples. a. Life process b. Reproduction c. Asexual reproduction d. Sexual reproduction

Oasis School Science and Technology - 8 125 e. Fission f. Binary fission g. Multiple fission h. Budding i. Sporulation j. Regeneration k. Vegetative propagation l. Complete flower m. Androecium n. Gynoecium o. Pollination p. Fertilization q. Self-pollination r. Cross-pollination s. Seed t. Monocotyledon seed u. Dicotyledon seed v. Gamete w. Germination x. Dispersal of seed 3. Very short questions a. Give any two examples of organisms that reproduce by fission. b. By which means of asexual reproduction yeast reproduces? c. What is the fertilization that takes place inside the body of a female organism called? d. A planaria broken into multiple pieces change into multiple planaria rather than dying. What type of asexual reproduction is it? e. What is the single unit of the female reproductive part of the flower called? f. What are the required conditions for germination? g. What do you mean cutting? Give an example of plant that reproduces by this process. h. What do you mean by layering? i. What is grafting? j. Define air layering. 4. Give reasons. a. Offspring from asexual reproduction is similar to parents. b. Asexual reproduction cannot help much in adaptation. c. Vegetative propagation is beneficial for agriculture. d. Farmers cut potato and plant them even though it has seeds. e. Vegetative propagation is used to grow new plants of banana. f. Sexual reproduction brings good traits in offspring. g. Bees are very important in the life cycle of the flowering plant. h. Seeds have micropyle. i. Some seeds have fur or hooks. j. Seed pods of sesame burst when touched. 5. Differentiate between a. Sexual and asexual reproduction b. Fission and fragmentation c. Binary fission and multiple fission

126 Oasis School Science and Technology - 8 d. Budding and sporulation e. Fragmentation and vegetative propagation by stem f. Pollination and fertilization g. Male gamete and female gamete h. Self-pollination and cross-pollination i. Internal fertilization and external fertilization j. Monocot seed and dicot seed 6. Short questions a. Why does a living thing reproduce? b. Write down the advantages and disadvantages of asexual reproduction. c. Enlist the advantages and disadvantages of sexual reproduction. d. What are the characteristics of asexual reproduction? e. What are the characteristics of sexual reproduction? f. Describe multiple fission of amoeba. g. How does budding occur in hydra? Represent it in a diagram. h. Draw the labelled diagram of the complete flower. i. Describe the structure of a complete flower. j. What is tissue culture? How is it done? 7. Long questions a. How do plants reproduce sexually? Describe with a neat and clean diagram. b. Describe sexual reproduction in animals. c. How does binary fission of amoeba occur? Describe with the help of a suitable diagram. d. Moss reproduces by sporulation. How does it occur? Explain with a diagram. e. What is vegetative propagation? Describe its types with suitable examples of each. f. How does the dispersal of seed occur in nature? Describe three possible ways for dispersal. g. How does pollination occur in nature? Describe three possible ways for pollination. h. Describe the structure of the monocot seed with a diagram. i. Describe the structure of the dicot seed with a diagram. j. Show by an activity that seeds need air, water and suitable temperature for germination. k. How is a new plant grown from cutting, layering, air layering and grafting? Describe in short.

Oasis School Science and Technology - 8 127 6 FORCE AND MOTION UNIT

128 Oasis School Science and Technology - 8 Key terms and terminologies 1. Rest : If the position of an object does not change with respect to other objects in its surroundings, it is said to be at rest. 2. Motion : If the position of the object changes with respect to other objects in its surroundings, it is said to be in motion. 3. Reference point : The body at rest with respect to which the state of another body is compared is called a reference point. 4. Uniform motion : A body is said to be in uniform motion if it covers an equal distance in an equal interval of time. 5. Non-uniform motion : A body is said to be in non-uniform motion if it does not cover an equal distance in an equal interval of time. 6. Vector quantity : Those physical quantities which have both magnitude and direction are called vectors or vector quantities. 7. Scalars : Those physical quantities which have only magnitude are called scalars. 8. Distance : The actual length travelled by a body is called distance. 9. Displacement : The shortest distance travelled by a body in a certain direction is called displacement. UNIT 6.1 MOTION Estimated teaching periods Theory 4 Practical 1  Introduction to relative velocity  Introduction to average velocity and simple calculations  Introduction to acceleration and simple calculations The Sequence of Curriculum Issued by CDC Sir Isaac Newton is world famous for his contributions to universal gravitation and laws of motion. He was born in England on 4th January 1643 and died on 31st March 1727. He was a mathematician, physicist, astronomer, alchemist and philosopher. He is known for his works in classical mechanics and optics. He with his friend Gottfried Wilhelm Leibniz developed infinitesimal calculus. He was educated (M.A) at Trinity College, Cambridge. About the Scientist Sir Isaac Newton

Oasis School Science and Technology - 8 129 10. Speed : Speed is defined as the rate of change of distance. 11. Velocity : Velocity is defined as the rate of change of displacement. 12. Uniform velocity : If a body covers equal displacement in equal intervals of time, the velocity of the body is called uniform velocity. 13. Variable velocity : If a body does not cover equal displacement in an equal interval of time, the velocity of the body is called variable velocity. 14. Average velocity : The mean of initial velocity and the final velocity of a moving body is called an average velocity. 15. Relative velocity : The velocity of a body with respect to another body is called relative velocity. 16. Acceleration : The rate of change in velocity is called acceleration. 17. Retardation : The negative acceleration or the rate of decrease in the velocity of a moving body is called retardation. Rest and motion In our surroundings, we see many things. Some of them can move from one place to another while some remain stationary. Birds, animals, vehicles, etc. change their position with respect to other objects in their surroundings. But house, tree, electric pole, tower, etc. do not change their position. Helicopter at rest Aeroplane in motion Fig. rest and motion If a body is not moving, we simply say it is at rest. If the position of an object does not change with respect to other objects in its surroundings, it is said to be at rest. If the position of the object changes with respect to other objects in its surroundings, it is said to be in motion. Rest and Motion are Relative Terms When you are sitting in a moving bus, the position of your body with respect to other seats or passengers remains constant. As compared to another passenger your position is not changing. So, you are at rest with respect to other seats or passengers. But distance between you and any tree near the Fig. bus is at rest with respect to tree

130 Oasis School Science and Technology - 8 road is changing as time passes. So, you are moving with respect to the tree. Thus, the same object at the same instant can be at rest with respect to one thing and in motion with respect to some other things. Motion is not absolute, neither is rest. The state of any object depends on the other objects with respect to which the position of a body is compared. Let us consider a bus at rest near a tree. When the bus starts to move, it changes its position with respect to the tree. Similarly, the driver also changes its position with respect to the tree. But the driver is not changing his position with respect to the bus. Therefore, the driver is at rest relative to the moving bus but he is in motion relative to the tree. Similarly, the tree is at rest relative to the moving bus and the moving bus is in motion relative to the tree. So, rest and motion are relative terms. Activity 1 • Observe the position of any ten objects like house, tree, bird, water, etc. Find out which are in a state of rest and which are in the state of motion. What can you conclude from this activity? Reference Point The body at rest with respect to which the state of another body is compared is called reference point. It is a certain point or place about which the state (rest or motion) of an object is studied. In the following figure, a car is moving near a tree. The car is in motion with respect to the tree. Here, the tree is taken as a reference point. Fig. Showing tree as a reference point Reasonable Facts Reference point is required to calculate relative velocity. To compare the state of a body at rest with respect to another body, reference point is required. It is impossible to compare the relative velocity between two bodies without any reference point. So, reference point is required to calculate relative velocity. Fact File If there is no reference point we cannot tell if an object is either at rest or motion.

Oasis School Science and Technology - 8 131 Uniform Motion and Non-uniform Motion A body is said to be in uniform motion if it covers equal distance in equal interval of time. 12m 12m 12m 12m 0s 1s 2s 3s 4s Fig: Uniform motion In the above figure, the car covers 12 m in every one second. Hence, the car is said to be in uniform motion. A body is said to be in non-uniform motion if it does not cover equal distance in equal interval of time. It is also called variable motion. In the above figure, the car does not cover equal distance in equal interval of time. So, it is said to be in non-uniform motion. Most of the bodies have variable motion, e.g. motion of a boy, motion of a vehicle, motion of air, etc. But the planets, stars and different machines have uniform motion. Activity 2 • Observe the motion of any five nearby objects. Watch them carefully and find out whether they are in a state of uniform motion or non-uniform motion. Vectors and Scalars Some physical quantities such as time, speed, distance, etc. can be described by their magnitude only but other physical quantities like velocity, force, displacement, etc. need magnitude as well as direction to describe them. Those physical quantities which have both magnitude as well as direction are called vectors or vector quantities, e.g. displacement, velocity, acceleration, force, etc. Vectors are written in a special way but scalars do not have any special way of writing the letters. For example: Vector AB is denoted byAB →. Reasonable Facts Velocity and acceleration are called vector quantities. Velocity and acceleration are called vector quantities because velocity and acceleration both have magnitude as well as directions. 8m 20m 10m 22m 0s 1s 2s 3s 4s Fig: Non-uniform motion

132 Oasis School Science and Technology - 8 Reasonable Facts Speed and mass are called scalar quantities. Speed and mass are called scalar quantities because speed and mass both have only magnitude but no direction. Those physical quantities which have only magnitude are called scalars or scalar quantities, e.g. distance, speed, mass, time, pressure, work, energy, area, volume, etc. Differences between Vectors and Scalars S.N. Vectors S.N. Scalars 1. Vectors have both magnitude and direction. 1. Scalars have only magnitude. 2. The sum of vectors may be positive or zero or negative. 2. The sum of scalars is always positive. 3. Vectors are added by the rules of vector algebra. 3. Scalars are added by the rules of simple algebra. Distance and Displacement Suppose a person is at place A. He has to reach B and then C. Now, the person starts from A and travels a distance of 4 km to reach B, and then travels another 3 km from B to C. Thus, the person goes along the path ABC. The total length AB + BC is the actual length to be covered. Thus, the actual length travelled by a body is called distance. In this example, actual path or distance travelled is AB + BC = 4 km + 3 km = 7 km. As the person reached the point C, we can find out how far he is from the initial point A or the shortest distance between A and C. The shortest distance (or distance of AC) is 5 km. The shortest distance travelled by a body in a certain direction is called displacement. Distance is a scalar quantity. Displacement does not depend on the path followed by a moving body but it depends only on the initial and final positions of a moving body. The SI unit of both distance and displacement is metre (m). 5 km 3 km 4 km Fig. distance and displacement C A B Fact File Distance is always taken as a positive quantity, whereas displacement is a vector quantity and it may have positive, zero or negative value.

Oasis School Science and Technology - 8 133 Activity 3 Draw a right angle triangle of any measurement. Label hypotenuses, perpendicular and base. Measure the length of base and perpendicular. Then measure the length of hypotenuses. Which measurement is distance and which measurement is displacement? Differences between Distance and Displacement S.N. Distance S.N. Displacement 1. Distance is the total length covered by a moving body in a certain interval of time. 1. Displacement is the shortest distance between initial and final positions of a moving body. 2. It is a scalar quantity. 2. It is a vector quantity. 3. It is always positive. 3. It can be positive, zero or negative. Speed and Velocity If a car travels a distance of 300 km in 5 hours, the speed of the car is 300/5=60 km/h, that is the car travels 60 km in every hour. Thus, the speed of a body gives the idea of how fast a body is moving but it does not indicate the direction of motion of the body. So, speed is defined as the rate of change of distance. Distance (s) Time taken (t) Speed = The SI unit of speed is m/s and its CGS unit is cm/s. But speed in a particular direction is called velocity. So, velocity is defined as the rate of change of displacement. Speed is a scalar but velocity is a vector quantity. Velocity (v) = Displacement (s) Time taken (t) The SI unit of velocity is m/s and its CGS unit is cm/s. Differences between Speed and Velocity S.N. Speed S.N. Velocity 1. Speed is the rate of change of distance. 1. Velocity is the rate of change of displacement. 2. It is a scalar quantity. 2. It is a vector quantity. 3. It cannot be zero. 3. It can be zero.

134 Oasis School Science and Technology - 8 Worked out Numerical 1 A car travels a distance of 30 km in 20 minutes towards the east. Calculate the velocity of the car. Solution: Displacement (s) = 30 km = 30 × 1000 m [∵ 1 km = 1000 m] = 30000m Time taken (t) = 20 min. = 20 × 60 = 1200 s [∵ 1 min. = 60 seconds] Velocity (v) = ? We know, v = s t = 30000 1200 = 25 m/s ∴ The velocity of the car = 25 m/s. Constant Velocity, Variable Velocity and Average Velocity Constant Velocity If a body covers equal displacement in equal interval of time, the velocity of the body is called constant velocity. It is also called uniform velocity. In the following figure, a car is moving from east to west. The car covers 8m in every one second. So, the velocity of the car is uniform velocity. Variable Velocity If a body does not cover equal displacement in equal interval of time, the velocity of the body is called variable velocity. In the above figure, a car is moving from east to west. The car covers different distances in every one second. So, the velocity of the car is variable velocity. 8m/s 0s 1s 2s 3s 4s Fig. Constant velocity 8m/s 8m/s 8m/s East West 7 m/s 10m/s 0s 1s 2s 3s 4s Fig. Variable velocity 8 m/s 12m/s East West

Oasis School Science and Technology - 8 135 Worked out Numerical 2 A person walks at 2 m/s for 10 minutes and then 1 m/s for 4 minutes. Calculate his average speed throughout his journey. Solution: For the first case, Time (t1 ) = 10 min. = 10 × 60s = 600 s [∵ 1 minute = 60 seconds] Distance travelled (s1 ) = speed × time = 2 × 600 = 1200 m For the second case Time (t2 ) = 4 min = 4 × 60s = 240 s Distance travelled (s2 ) = speed×time= 1 × 240 = 240 m Average speed = s s t t 1 2 1 2 + + = 1200 240 600 240 + + = 1440 840 = 1.71 m/s ∴ The average speed of the person is 1.71 m/s. Average Velocity The mean of initial velocity and the final velocity of a moving body is called an average velocity. Average velocity (vav) = initial velocity u( ) + final velocity v( ) 2 Worked out Numerical 3 A person takes 8 minutes to cover a distance of 15 kilometres in his car. Calculate the average velocity of his car. Solution: Given, Time taken (t) = 8 minutes = 8×60 seconds [ ∵ 1 min. = 60 seconds] = 480 s Distance covered (s) = 15 kilometres = 15×1000 metres [ ∵ 1 km = 1000 m] = 15000 m Average velocity (v) = ? We know, vav = s t = 15000 480 = 31.25 m/s ∴ The average velocity of the car is 31.25 m/s. ∴ vav = u v + 2

136 Oasis School Science and Technology - 8 Relative Velocity The velocity of a body with respect to another body is called relative velocity. a. Two bodies moving along the same direction Let us consider two cars moving along a straight road in the same direction as shown in the fig. (a). In this case, the velocity of a body with respect to another body is given by Velocity of car A with respect to B (vAB) = velocity of car A (vA) – velocity of car B (vB). i.e. vAB = vA – vB b. Two bodies moving in the opposite direction Let us consider two cars A and B are moving in the opposite direction. Let velocity of the car A be vA and velocity of car B be vB. Since the direction is opposite, so velocity of car A with respect to car B = vAB i.e. vAB = Velocity of car A - Velocity of car B. = vA - (-vB) [ ∵ vB is negative as it moves in opposite direction] ∴ vAB = vA + vB X X Y Y A A B 10 m/s B 10 m 25 m/s 25 m Initial position After 1 second Fig. Thus, when two cars are moving in opposite direction, they appear to move with higher velocity. Fig. 2.9 B B X X Y Y A A 10 m/s 25 m/s 25 m 10m Initial position After 1 second

Oasis School Science and Technology - 8 137 Worked out Numerical 4 Two vehicles X and Y are moving in the same direction with the velocity of 12 m/s and 6 m/s respectively. Calculate the relative velocity of X with respect to Y. If both vehicles are travelling in the opposite direction, what will be the relative velocity ? Solution: Here, Velocity of X (vx ) = 12 m/s Velocity of Y (vy ) = 6 m/s When they are moving in the same direction, Relative velocity of X with respect to Y (vxy) = vx – v y = 12 – 6 = 6 m/s. When they are moving in the opposite direction, v xy = vx – v y Here, vy is negative ( ∵ vx is opposite to vy ) So, vxy = 12 – (-6) = 12 + 6 = 18 m/s ∴ Relative velocity is 18 m/s. Worked out Numerical 5 Two vehicles X and Y are moving with the velocity of 20 m/s towards east and 12 m/s towards west respectively. If they started from the same place and the same time, calculate the distance between them after 2 minutes. Solution: Here, Velocity of vehicle X (v1 ) = 20 m/s (towards east) Velocity of vehicle Y (v2 ) = 12 m/s (towards west) Time taken (t) = 2 min. = 2×60 s = 120 s Distance travelled by vehicle X (s1 ) = v1 ×t = 20×120 = 2400 m Distance travelled by vehicle Y (s2 ) = v2 ×t = 12×120 = 1440 m ∴ Distance between the two vehicles (s) = s1 + s2 = 2400 + 1440 = 3840 m Acceleration and Retardation When a body is moving with an increasing velocity, the body is said to be accelerated. Suppose a body is moving from rest and the velocity of the body reaches 10m/s in 5

138 Oasis School Science and Technology - 8 seconds. The change in velocity of the body is 10 m/s – 0 m/s. Thus, in every second velocity changes by 10 5 m/s = 2m/s. The body is said to have changing velocity of 2 m/s in every second. It means that the body is accelerating at a rate of 2m/s2 . The rate of change in velocity is called acceleration. Its SI unit is metre per second per second (m/s2 ). The acceleration of a moving body is calculated by the given formula. Acceleration (a) = Change in velocity Time taken Acceleration (a) = Final velocity (v) – Initial velocity (u) Time taken (t) ∴ a = v–u t The negative acceleration or the rate of decrease in velocity of a moving body is called retardation. It has the same unit as that of the acceleration, i.e. m/s2 . A moving body is said to be in the state of retardation when its velocity decreases. Differences between acceleration and retardation Acceleration Retardation 1. The rate of increase in velocity of a moving body is called acceleration. 1. The rate of decrease in velocity of a moving body is called retardation. 2. It is positive value. 2. It is negative value. Reasonable Facts The object having uniform velocity has zero acceleration. The object having uniform velocity has zero acceleration because the object having uniform velocity has the same initial and final velocity. Worked out Numerical 6 Calculate the acceleration of a truck if it starts from rest and attains a velocity of 25 m/s in 5s. Solution: Initial velocity (u) = 0 (∵ The truck starts to move from rest.) Final velocity (v) = 25 m/s Fact File An object with uniform velocity has zero acceleration.

Oasis School Science and Technology - 8 139 Time (t) = 5s Acceleration (a) = ? We have, a = v–u t = 25–0 5 = 5 m/s2 . ∴ The acceleration of the truck is 5m/s2 . Activity 4 • Bring a measuring tape and measure the distance of 100 m in the school ground. Mark the distance by using lime powder. • Now, ask your friends to cover that distance one by one and measure the time taken by each of them to cover the distance of 100 m. • Calculate the velocity of each of the friends. • Now, ask two friends to cover that distance and calculate the relative velocity. Reasonable Thinking Skill R T S 1. The earth travels at a very high velocity but we do not feel it. The earth travels at a very high velocity but we do not feel it because it has uniform velocity and zero acceleration. 2. When two buses are moving in the same direction with equal velocity, the first bus appears to be at rest as viewed from the second bus. When two buses are moving in the same direction with equal velocity, the first bus appears to be at rest as viewed from the second bus because their relative velocity is zero. 3. An object that travels in a linear path with a uniform velocity has zero acceleration. If an object is travelling in a linear path with a uniform velocity, it is not changing direction and its initial and final velocity will be equal. Therefore, change in velocity (final velocity – initial velocity) will be zero. Hence there will be no change in velocity. Therefore, acceleration will be zero. 4. Velocity is a vector quantity. Velocity is a vector quantity because it has a magnitude and a direction. 5. What will be the final velocity of an object if it is thrown vertically upward with an initial velocity of 25 m/s? The final velocity of an object will be zero when it is thrown vertically upward despite any magnitude of the initial velocity.

140 Oasis School Science and Technology - 8 6. A car has an initial speed of 25 m/s. When brakes are applied then after 2 seconds its speedometer records a speed of 10 m/s. Find the acceleration of the car. Solution: Initial velocity (u) = 25 m/s Final velocity (v) = 10 m/s Time (t) = 2 seconds Acceleration (a) = ? Using formula , a = v–u t = 10–25 2 = – 15 2 = -7.5 m/s² 7. Nothing is at absolute rest. Explain. Nothing is at absolute rest because every object in the universe is in motion. For example, a house may seem at rest but it is travelling along with the earth. Earth moves around the sun. Sun moves around the centre of the galaxy. All the galaxies are moving away from each other in the universe. The universe itself is expanding. Exercises 1. Choose the best answer from the given alternatives. a. What is the condition called when an object cannot change its position with respect to its surrounding? i. relative velocity ii. motion ii. rest iv. uniform velocity b. Which of the following is a vector quantity? i. distance ii. pressure iii. speed iv. velocity c. What is the rate of change of distance called? i. speed ii. velocity iii. acceleration iv. retardation d. Which of the following is the average velocity? i. v+u 2 ii. u–v 2 iii. u+a 2 iv. u+v t e. Which of the following is the SI unit of acceleration? i. ms2 ii. m/s–2 iii. m/s2 iv. cm/s2 2. Define the following with required examples. a. Rest b. Motion

Oasis School Science and Technology - 8 141 c. Reference point d. Uniform motion e. Non-uniform motion f. Vector g. Scalar h. Distance i. Displacement j. Speed k. Velocity l. Uniform velocity m. Variable velocity n. Average velocity o. Relative velocity p. Acceleration q. Retardation 3. Very short questions. a. Which physical quantities have both the magnitude and the direction? b. What is the rate of change of displacement called? c. What is the mean of initial and final velocity called? d. What is the rate of decrease in velocity defined as? e. Write the SI unit of retardation. 4. Give reasons. a. Reference point is necessary to define rest and motion. b. Rest and motion is a relative term. c. Revolution of the moon around the earth is called uniform motion. d. Displacement is called a vector quantity. e. Distance is called a scalar. f. If two vehicles are travelling in the same direction, the first vehicle seems travelling slowly when we see it from the second vehicle, even though it is travelling at a higher speed. g. Even though the earth is travelling at a very high speed, we do not feel it. 5. Differentiate between: a. Rest and Motion b. Vectors and Scalars c. Speed and Velocity d. Constant velocity and Variable velocity e. Acceleration and Retardation 6. Short question answers a. What does it mean by the fact that the acceleration of a car is 5 m/s²? b. Velocity of an object is 25 m/s. What does it mean? c. What is the condition in which relative velocity between two objects travelling in the same direction becomes zero? d. When does an object has constant speed but changing velocity?

142 Oasis School Science and Technology - 8 7. Long question answers a. How is the relative velocity calculated when: i. the two bodies A and B are moving in a straight line in the same direction. ii. the two bodies A and B are moving in a straight line in the opposite direction. b. In which condition the relative velocity of the two bodies moving in the same direction becomes zero? c. Acceleration and retardation are opposite to each other. A ‘car A’ is moving towards east with a velocity of 70 km/h and another ‘car B’ is moving towards west with a velocity of 50 km/h. Find their relative velocity. Also, find their relative velocity if they move in the same direction 8. Numerical Problems a. Two vehicles X and Y are moving in the same direction with the velocity of 12 m/s and 8 m/s respectively. Calculate the relative velocity of X with respect to Y. Also, calculate the relative velocity when they are moving in opposite directions. [Ans: 4 m/s, 20 m/s] b. Two vehicles are moving, one with the velocity of 20 m/s towards east and another with 10 m/s towards west. Calculate the distance between them after 20 minutes if they are started from the same place and the same time. [Ans: 36000 m] c. If a body starts from rest and attains a velocity of 20 m/s in 8 seconds, calculate the acceleration produced on the body. [Ans: 2.5 m/s2 ] d. A vehicle is running at a speed of 45 km/h. If it is stopped in 3 seconds by applying the brakes, calculate the retardation of the vehicle and the distance travelled before its stopping. [Ans: 4.16 m/s2 , 18.75 m] e. The velocity of a moving body increases from 10 m/s to 15 m/s in 5 seconds. Calculate its acceleration and average velocity. [Ans : 1m/s2 , 5m/s] f. A body moving along a straight path at a velocity of 20 m/s attains an acceleration of 4 m/s2 . Calculate the velocity of the body after 2 seconds. [Ans: 28 m/s] g. A vehicle was moving at a speed of 90 km/h. On seeing a baby 20 m ahead on the road, the driver jammed on the brakes and it came to rest at a distance of 15m. What is its retardation and how long does it take to come at rest? [Ans: 20.83 m/s2 , 1.2 s] h. A body starts moving from rest and attains the acceleration of 0.5 m/s2 . Calculate the velocity at the end of 3 minutes. Also, find the distance travelled by it during that time. [Ans: 90 m/s, 8100 m]

Oasis School Science and Technology - 8 143 UNIT 6.2 SIMPLE MACHINES Estimated teaching periods Theory 4 Practical 1  Introduction to lever and its types  Working principles of the lever  Introduction to mechanical advantage, velocity ratio and efficiency and simple calculations The Sequence of Curriculum Issued by CDC Archimedes of Syracuse is well known for Archimedes principle developed to find the volume of irregular solids which could be used to find the purity of metals. He was born in Ancient Greece, the ancient city of Syracuse in Sicily in 287 BC and died in 212 BC. He was a Greek mathematician, physicist, engineer, astronomer and inventor. He discovered the centre of gravity, the law of lever and Archimedes’ screw. About the Scientist Archimedes of Syracuse Key terms and terminologies 1. Machine : A device which makes our work easier, faster and more convenient is called a machine. 2. Simple machine : The devices with simple body structures that are used to make our work easier and faster are called simple machines. 3. Effort : The force applied to a machine to do mechanical work is called effort. 4. Load : The force applied by the machine on the body on which the work is done is called load. 5. Mechanical advantage : The ratio of the load to the effort is called mechanical advantage. 6. Velocity ratio : The velocity ratio is the ratio of the distance travelled by an effort to the distance travelled by the load. 7. Output work : The work done by a machine is called output work. 8. Input work : The work done in a machine is called input work. 9. Efficiency : The percentage ratio of output work to input work is called the efficiency of a machine.

144 Oasis School Science and Technology - 8 10. Ideal machine : The machine with 100% efficiency due to the absence of friction is called an ideal (or perfect) machine. 11. Lever : A lever is a rigid bar which stands in the fulcrum and rotates on it. 12. Fulcrum : The fixed point about which a lever can rotate freely is called a fulcrum. 13. Principle of lever : According to the principle of the lever, “For an ideal lever, the input work is always equal to the output work.” 14. First class lever : The lever in which the fulcrum lies in between load and effort is called the first class lever. 15. Second class lever : The lever in which load lies in between fulcrum and effort is called the second class lever. 16. Third class lever : The lever in which effort lies between load and fulcrum is called the third class lever. Introduction Modern age is the age of machines. Today our lives are made easier by a variety of mechanical devices called machines. We use a variety of machines in our daily life. Machines help us to perform mechanical work by using muscular energy. A device which makes our work easier, faster and more convenient is called a machine. We can do various works with the help of different machines. Some machines are simple in structure while others are complex. Those machines which are simple in structure are called simple machines. A particular simple machine helps us to do a particular work only. The devices which are used to make our work easier, faster and to change the direction of force are called simple machines. For example, scissors, crow bar, beam balance, fire tongs, pulley, knife, etc. Simple machines are very useful to us because they help to multiply the force, apply force in a convenient direction, apply force at a convenient point and to gain speed. Fig. Some simple machines Scissors Beam balance Wheel barrow Pulley Screw Axe 3.2 Applications of Simple Machines i. Simple machines help to multiply force. ii. They help to change the direction of force. iii. They help to increase the speed of work. iv. They help to do work safely.

Oasis School Science and Technology - 8 145 Reasonable Facts Simple machines are widely used in our daily life. Simple machines are widely used in our daily life because simple machines make our work easier, faster and change the direction of the force applied. Technical Terms Related to Machines a. Effort (E) : The force applied to a machine to do mechanical work is called effort. b. Load (L): The force applied by the machine on the body on which the work is done is called load. For example, a crowbar is used to lift heavy objects. In this, load is the weight of the body to be lifted. c. Mechanical Advantage (MA): The ratio of the load to the effort is called mechanical advantage, i.e. MA = Since mechanical advantage is the ratio of two similar quantities, i.e. forces, it has no unit. If the load lifted by a machine is greater than the effort applied, the mechanical advantage is greater than 1 (MA>1). If the load lifted is less than the effort applied, the MA is less than 1 [MA<1]. MA depends on friction and the weight of a machine. If friction increases, MA decreases. No machine is frictionless. Due to the presence of friction, large amount of effort is wasted. Similarly, due to the weight of a machine, the mechanical advantage becomes less. d. Velocity Ratio (VR): Velocity ratio is the ratio of the distance travelled by effort to the distance travelled by load. VR = Distance travelled by effort Distance travelled by load Effort distance Load distance = VR of a machine is not affected by the friction or weight of a machine. It has no unit since it is the ratio of two similar quantities, i.e. distance. e. Output work and input work: The work done by a machine is called output work. It is the product of load and the distance travelled by load. Similarly, the work done on a machine is called input work. It is the product of effort and the distance travelled by effort, i.e. Output work = load × distance travelled by load Input work = effort × distance travelled by effort f. Efficiency (ŋ): The percentage ratio of output work to input work is called efficiency of a machine. It is expressed in percentage and denoted by the letter eta (ŋ). Efficiency (ŋ) = × 100% Output work Input work Load(L) Effort (E)

146 Oasis School Science and Technology - 8 Relation among MA, VR and ŋ Efficiency (ŋ) = × 100% Output work Input work = Load×distance travelled by load Effort×distance travelled by effort Distance travelled by effort Distance travelled by load × 100% Load Effort × 100% = = MA VR × 100% This is the required relation among MA, VR and ŋ. Activity 1 Measure your and your friend's mass. Calculate weight. Weight = mass x acceleration due to gravity. Play see-saw. Measure the distance from each of you to the fulcrum. Calculate efficiency of the see-saw when you are playing it. Reasonable Facts The mechanical advantage of a simple machine is always less than the velocity ratio. The mechanical advantage of a simple machine is always less than the velocity ratio because mechanical advantage is affected by the friction and weight of the machine whereas velocity ratio is not affected by the friction and weight of the machine. Reasonable Facts The efficiency of a machine is always less than 100%. Efficiency of a machine is always less than 100 % because the output work is less than input work and MA is less than VR due to the friction. Efficiency of a machine can also be defined as the percentage ratio of mechanical advantage (MA) to the velocity ratio (VR) of the machine. Efficiency is the ratio of two works done. So, it has no unit. MA and ŋ are affected by the friction but not VR. So, MA is always less than VR and the efficiency of a machine can be increased by reducing the friction. Some of the ways to reduce friction are using grease, ball-bearings, making the surface smooth, etc. Fact File Mechanical advantage is affected by the friction but velocity ratio is not. ∴ ŋ = MA VR × 100%