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1. A force can cause a change in state and direction of an object. 2. An interaction between two objects causes a force. 3. Force applied by direct touching an object is called contact force. 4. Gravitational force is an example of non contact force. 5. Liquid exerts pressure in all direction. 6. Air exerts pressure on the earth due to its weight. 7. Atmospheric pressure is measured by using barometer is made by E. Torricelli. 8. Aneroid barometer does not use any liquid 9. Gases and Liquid are collectively called Fluid. Match the Coolum 1. Earth revolving around the sun->gravitational force 2. A force applied by touching-> Contact force 3. Force between two charged object->electrostatic force 4. Bloating of the tube of cycle tyre -> air pressure 5. Force applied per unit area-> pressure State true or false 1. A player kicking football in an example of a non contact force-> F 2. Liquid and gases do not exert pressure-> F 3. Pressure in liquid decreases with depth -> F 4. Like charges repel and unlike chare attract each other-> T 5. Magnetic pole attract magnetic substance like iron-> T Think Zone Q. What is the role of air pressure in the filling of a syringe with a liquid medicine, by a doctor? Answer: The air pressure plays an important role in the filling of syringe as the liquid medicine rushes into the syringe when air pressure inside it decreases on pulling piston out. Q. Why do people with high blood pressure sweat a lot? Answer: This is because the pressure of their body fluid becomes more than atmospheric pressure .This forces the water to ooze out easily. Q. There is a famous saying n Hindi a sword cannot replace a needle .Give reason for the saying in the light of physics Answer: In the physics, the pressure applied on needle gets concentrated its tip i.e. on very small area and hence it pierces the cloth easily. But to make the sword cut a surface; we have to apply much higher pressure due to large surface area of the cutting edge of the sword. Hence a sword cannot replace a needle. Q. Every square centimeter of our body experience atmospheric force equal to mass of 100kg that is enough to grind us. Then why do people cannot crushed by atmospheric pressure? Answer: this is because there is pressure exerted by our body due to flow of blood that equalizes atmospheric pressure. Q. A plastic comb when rubbed with hair can attract piece of paper. Name force and its nature? Answer: Electrostatic Force. It is generated when a charged body meets to another charged or by rubbing two uncharged body. Q. Why it is not easy to walk wearing high heels shoe? Ans: High heels shoe distribute a large amount force in a Small area hence making her feel uncomfortable while walking on ground. Q. Give two uses of fluid pressure? Ans: Cooling, Cooking, filling LPG in cylinder Q. Give reason: (a)A rolling ball stops after moving some distance Answer: This is because of friction force of the ground that opposes motion. (b) Every object left above the surface of the earth without a support, fall downwards. Answer: This is due to gravitational pull of the earth. (c) If gravitational force act between you and your friend. Then why should not you pull each other? Answer: Gravity only becomes noticeable when there is a really massive object like a moon, planet or star. Due to small masses no force of gravity is noticed. Class VIII Mathematics [Click on links given below] VIII Algebra VIII Commercial Maths VIII Geometry & Menstruation CBSE Class VIII Science Physics Chemistry Biology 8th Sample paper 8th Social Science
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8th Science Chapter 3 - Synthetic Fibres and Plastics[Solved Questions]
Q. Name some natural fibres? Answer: Fibres obtained from plants or animals is called natural fibres for examples cotton, wool, silk, etc. Q. What do you mean by synthetic fibres? Answer: Fibres made by human beings using chemical substance is called synthetic fibre. A synthetic fibre is a chain of small unit of chemical substance joined together. These small units combine to form a large single unit called a polymer. The word ‘polymer’ comes from two Greek words; poly meaning many and mer meaning part/unit. So, a polymer is made of many repeating units. Q. Name a polymer occurs naturally? Answer: Polymers that occur naturally is cellulose. Cellulose is made up of a large number of glucose units. Q. Name a fibre having properties similar to that of silk. Answer: Rayon. Q. Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. Why? Answer: This is because rayon is obtained by chemical treatment of wood pulp. Q. Why does Nylon become very popular for making clothes for mankind? Answer: Nylon is the first fully synthetic fibre prepared from coal, water and air in 1931. Nylon fibres are strong, elastic and light. It is lustrous and easy to wash. So, it became very popular for making clothes. Q. Is nylon fibre really so strong that we can make nylon parachutes and ropes for rock climbing? Answer: Yes, It is because nylon thread is actually stronger than a steel wire. Q. Why does polyester fibre quite suitable for making dress material? Answer: Fabric made from Polyester fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material. Terylene is popular polyester. Q. Name a form of polyster which is used for making bottles, utensils, films, wires and many other useful products? Ans: PET: PET (polyethylene terephthalate) is made from two monomers, terephthalic acid and ethylene glycol, by the process called condensation polymerization Q. Name the chemical used to make polyster? Answer: Esters are the chemicals used to make polyster. Q. Why synthetic fibres are more popular than natural fibres? Answer: Synthetic fibres dry up quickly, durable, less expensive, readily available and easy to maintain which makes them more popular than natural fibres. Q. Identify the Synthetic fibre appears to resemble wool? Answer: acrylic. Download full paper by clicking links given below8th Synthetic fiber and Plastic [Solved Questions] Download File VIII Synthetic fiber and Plastic Read and download VIII Synthetic fiber and Plastic Read and download Q. What are crops? Answer: The same kind of plants grown and cultivated at one place on a large scale is called a crop. For example, wheat, maize, etc Q.What is the different types of crops grown in India? Ans: These are: (i) Kharif Crops : The crops which are sown in the rainy season (from June to September)are called Kharif crops. Paddy, maize, soya bean, groundnut, cotton, etc., are kharif crops. (ii) Rabi Crops : The crops grown in the winter season (October to March )are called rabi crops. Examples of rabi crops are wheat, gram, pea, mustard and linseed. Q. Why is proper agricultural management and distribution of food necessary ? Answer: In order to provide food for a large population—regular production, proper management and distribution of food is necessary. Q. Why can paddy not be grown in the winter season? Answer: Paddy requires a lot of water. Therefore, it is grown only in the rainy season. Q. List different agricultural practice ? Answer: The agricultural practices are listed below. (i) Preparation of soil (ii) Sowing (iii) Adding manure and fertilizers (iv) Irrigation (v) Protecting from weeds (vi) Harvesting (vii) Storage Q. Why does the loosening of soil allow the roots to breathe easily? Answer: The process of loosening and turning of the soil is called tilling or ploughing.This is done by using a plough. The air enters easily through loosen soil and the root can breathe easily even when they go deep into the soil. Q. Why earthworms are called farmers friends? Ans: The loosened soil helps in the growth of earthworms and microbes present in the soil. These organisms are friends of the farmer since they further turn and loosen the soil and add humus to it. Q.why does the soil need to be turned and loosened before seeds are sown? Answer: Since only a few centimeters of the top layer of soil supports plant growth, turning and loosening of soil brings the nutrient-rich soil to the top so that plants can use these nutrients. Q. What are the purposes of the leveling of soil? Answer: The ploughed field may have big pieces of soil called crumbs. It is necessary to break these crumbs with a plank. The field is levelled for sowing as well as for irrigation purposes. The levelling of soil is done with the help of a leveller. Q.Why we sometimes add manure to the soil before tilling? Answer: This helps in proper mixing of manure with soil. Q. Name some agricultural Implements? Answer: The main tools used for agriculture purpose are the plough, hoe and cultivator. Q.How can we separate good, healthy seeds from the damaged ones? Answer: We put seeds into bucket full of water. Damaged seeds being hollow became lighter therefore they float on water and remaining good seeds sink at bottom. Q. Why sowing seeds with seed drill is better than by hand? Answer: Practice of sowing seeds by hand is called broadcasting. The seed drill is used for sowing with the help of tractors. This sows the seeds uniformly at proper distances and depths. It ensures that seeds get covered by the soil after sowing. This also prevents damage caused by birds. Full notes download link ![]()
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Macro-Micro Nutrients-Manures-Fertilizers Read Crop Production and Management Practice Paper-1 Read/Download Crop Production and Management Practice Paper-2 Read/Download Crop Production and Management [Solved] Practice Paper -3 Download File Q.1 Fill in the blanks:-
(i) By volume about _______ of air is nitrogen and about _________ is oxygen. [78% ,21% ] (ii) Incomplete burning of fuels produces ________ which is a _______ gas. [carbon mono oxide, poisonous] (iii) Carbon monoxide _________ the oxygen carrying capacity of the blood. [Reduce] (iv) Petroleum refineries are a major source of gaseous pollutants like ______ and ______. [sulphur dioxide and nitrogen dioxide.] (v) _______ used in refrigerators damages the ozone layer of the atmosphere. [ chlorofluorocarbons] (vi) Ozone layer protects us from the harmful ________ rays of the sun. [Ultra Violet ] (vii) _______ of the world’s population is without safe drinking water. [25%] (viii) We can save water by remembering the 3R’s ____, ____ and ________. [Reduce, reuse and recycle] (ix) Acid rain is formed by the oxidation followed by dissolution of ________ and gases in rain water. [water vapour] Q.2. Define air pollution. What are air pollutants? Ans: When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as air pollution. The substances which contaminate the air are called air pollutants. Q.3. what are the various sources of air pollutants? Ans: Natural sources like smoke and dust arising from forest fires or volcanic eruptions. Human activity like factories, power plants, automobile exhausts and burning of firewood and dung cakes. Q.4. what is smog? Why is it harmful? Ans: A thick fog-like layer in the atmosphere, especially during winters. This is smog which is made up of smoke and fog. The smog causes breathing difficulties such as asthma, cough and wheezing in children. Q.5. What is acid rain? Ans: Sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain. Q.6 How is the Taj Mahal affected by air pollution? Ans: Pollutants in air are discolouring its white marble. Q.7 What is meant by ‘Marble Cancer’? Ans: Acid rain corrodes the marble of the monument. The phenomenon is also called “Marble cancer”. Q.8 Write the full forms (i) CFC (ii) CNG (iii) LPG (iv) WWF Ans:(i) chlorofluorocarbons(ii)Compress natural gas(iii) Liquefied petroleum gas(iv) World Wide Fund Q.9 what is greenhouse effect? Name four greenhouse gases. Ans: A part of the radiation that falls on the earth is absorbed by it. The trapped radiations further warm the green house earth. This is called the greenhouse effect. CO2 ,CH4 , N2 O, SO2 Q.10 Write a note on global warming. Ans: Greenhouse gases like CO2 traps Sun’s heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming. Q.11 What is Van Mahotsav? Ans: Van Mahotsav is an annual tree-planting festival in India, celebrated in the first week of November. Q.12 Why does the increased level of nutrients in the water affect the survival of aquatic organisms? Ans: The increased level of nutrients in the water, enhance the growth of algae in the water body. Once the algae dies, they serve as food for decomposers like bacteria. For the decomposition, a lot of O2 in the water body decreases and may kill aquatic organisms. Q.13 Why do we say that the river Ganga is dead at many places? Ans: This is because the pollution levels are so high that aquatic life cannot survive. Q.14 What is potable water? Ans: Water which is suitable for drinking is called potable water Q.15. What are the various methods by which water can be made safe for drinking? Ans: The various methods by which water can be made safe for drinking are: (a) Using candle type filter (ii) boiling (iii) by adding chlorine tablets or bleaching powder to the water 1. Explain the following terms:-
(a) Reproduction- The process of giving rise to new organisms of the same species. (b) Fertilization-The fusion of male & female gametes. (c) Zygote- The single-celled structure formed on the fusion of male & female gametes. (d) Metamorphosis- The gradual transformation of an organism from one form to another during its life cycle (e) Hermaphrodites-The organisms having both male & female reproductive organs in the same body. Eg:- Earthworm, Leech (f) Foetus- The multicellular structure formed after the repeated cell divisions in the Zygote formed as a result of fertilization. (g) Larva- The active form that emerges from the eggs . (h) Placenta- The specialized tissue that attaches the developing foetus to the uterine wall & provides for it nourishment, respiration & excretion. 2. Give reasons for the following:- (a) Gender of the resulting offspring is determined by the male parent in humans. Ans- The Y-chromosome bearing sperm that fertilizes an ovum results in a male offspring. The X-chromosome bearing sperm that fertilizes an ovum results in a female offspring. (b) Sex hormones regulate secondary sexual characters. Ans- The functioning of our reproductive organs is regulated by the sex hormones and one of the functions is the appearance of secondary sexual characters at puberty. (c) Platypus & Echidna lay eggs but are not oviparous animals. Ans- They lay eggs but feed the young ones on milk through the mammary glands. (d) Sperm needs to have motility. Ans – Sperms have to enter the female reproductive passage and fertilize the ovum by travelling through the vagina & uterus for this in the fallopian tube/ oviduct. LONG ANSWER TYPE QUESTIONS:- 1. Explain where the embryo stays till it is fully developed and also explain how its nutritional , respiratory & excretory functions are carried out. Ans- The embryo gets attached to the uterine wall through the Placenta which is a specialized tissue richly supplied by blood & takes care of all the developmental functions of the developing embryo- nutrition, respiration & excretion. 2. What is Asexual reproduction? What are the advantages of this method? Ans- The mode of reproduction that involves a single organisms & also doesn’t require any special organs or cells. Its advantages are:- (a) Offsprings produced are identical to the parents so desired traits can be transmitted to the next generation (b) A quick method of reproduction (c) Only one parent organism is required, no special organs or cells also required. 3. Explain the meaning of Binary Fission. Name a few organisms that reproduce like this & draw a series of diagrams to demonstrate this process in Amoeba. Ans- The method by which an organism divides into two equal halves . Other organisms are:- Paramecium, Euglena, Bacteria. Refer to figure 9.12 of NCERT 4. Explain how budding occurs. Name a few organisms that reproduce like this & draw a series of diagrams to demonstrate this process in Hydra. Ans- Small bulges appear on the sides of the body of the organisms that gradually develop into new organisms. Sponges & Yeast besides Hydra. Refer to figure 9.11 of NCERT 5. What is Metamorphosis? With the help of flow diagrams illustrate the life cycles of a Silkworm & Frog. Ans- Metamorphosis- The gradual transformation of an organism from one form to another during its life cycle. Silkworm:- Egg -->Larva/ Caterpillar--->Pupa/ Cocoon---> Adullt Frog:- Egg---> Tadpole(Larva)- --> Froglet- --> Adult Frog |
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