Express Notes Science Form 2
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  • I am very happy to read your articles it’s very useful for me, 
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    The writings are small due to shrinkages on the screen. My suggestion is to download it and print on an A4 paper, or better still, open it up on an iPad and you can increase the image without losing too much of its resolution. Good luck!
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    Express Notes Science Form 2 Express Notes Science Form 2 Presentation Transcript

    • Written By Ng Chee Kin B.Sc.(Hons.), MBA ngcheekin@gmail.com mrcheekin@blogspot.com.auAll Rights Reserved ©2012 Ng Chee Kin
    • Page 1 PREsSS E X p r e����� u .a 2 The tongue: CHAPTER 1 om Fine hair The World through Our Senses Bitter Epidermis Pain receptor 1.1 Sensory Organs Sour Heat t.c receptor 1 Humans have five senses. Table 1 shows the Dermis Salty Pressure senses, sensory organs and stimulus detected. receptor Cold Sweet Sense Sensory organ Stimulus receptor po Fatty layer Touch Touch, pressure, 1 Chemical particles 2 Taste projections receive receptor Touch Skin dissolve in saliva stimulus and send it to cold, heat, pain on the surface of the taste receptors the tongue Chemical gs Smell Nose 2 The sensitivity of skin depends on: substances in air 3 Taste receptor (a) the closeness of receptors Chemical sets off impulse Taste Tongue (b) the depth of receptors substances in food 4 Impulse is sent to lo Taste bud the brain to be Hearing Ear Sound 1.3 Sense of Smell interpreted as taste Sight Eye Light .b 1 The roof of the nasal cavity has many sensory cells to detect smells. 1.5 Sense of Hearing Table 1 4 Impulses are sent to the brain 1 The human ear: in 2 Each sensory organ has receptors to detect 3 Nerve sends nerve impulse to stimuli. Pinna Ossicles the brain to be interpreted 3 Pathway from stimulus to responses: Nerve impulse Semicircular ek canal 2 Receptor cell detects smell and Stimuli sensory organ nerves brain generates nerve impulse Ear Auditory canal nerve responses effectors nerves Nasal 1 Cilium contains mucus to cavity dissolve inhaled particles Cochlea he 4 Nerve impulses are electrical messages produced To the brain Eardrum Eustachian Nostril Oval window by receptors. tube 5 Effectors are organs which carry out responses. Into the lungs 6 Responses are reactions which occur after 2 The mechanism of hearing: rc receiving a stimulus. Pinna ear canal eardrum ossicles 1.4 Sense of Taste 1.2 Sense of Touch auditory cochlea oval window m 1 The surface of the tongue has many taste buds to detect chemical substances. nerve brain 1 The skin has five receptors.WB Science F2 (Exp Note) 1st.indd 1 4/2/2009 5:48:16 PM
    • Page 2 1.6 Sense of Sight 4 Devices to overcome the limitations of sight: 1.9 Stimuli and Responses in Plants Microscope, telescope, magnifying glass, 1 The human eye: 1 Tropism is a growth response to external stimuli. u periscope, x-ray, binoculars and ultrasound Vitreous humour scanning device Choroid Tropism Stimuli Example .a Supportive ligament 5 Stereoscopic vision helps predators to detect the Retina Iris location of their preys accurately. The roots grow Sclera Lens 6 Monocular vision helps prey to detect their Hydrotropism Water towards a water Yellow spot om Cornea enemies from all directions. source Optic nerve Pupil The roots grow in Aqueous humour 1.8 Sound and Hearing Geotropism Gravity the direction of 1 Properties of sounds: gravity Ciliary muscle Conjunctiva Blind spot t.c (a) they are produced by vibrations of objects. 2 The retina has photoreceptors to detect light. The shoots grow (b) they need a medium to travel, such as solids, Phototropism Light 3 Mechanism of sight: towards sunlight liquids or gases. (c) they cannot travel through a vacuum. The tendrils wrap Cornea aqueous humour lens Touch po (d) they can be absorbed by soft and rough Thigmotropism around a solid optic nerve retina vitreous humour (contact) surfaces. structure (e) they can be reflected by hard and smooth brain optic effectors nerves surfaces as echoes. 2 Nastic movements are responses of plants to gs 2 Stereophonic hearing helps to detect the location external stimuli which may come from any 1.7 Light and Sight of the source of sound. direction. 1 Reflection of light happens when it bounces off lo the surface on which it falls. 2 Refraction is the bending of light due to speed CHAPTER 2 change as it travels through transparent medium Nutrition of different densities. 3 Defects of vision: 2.1 .bClasses of Food in Defects of Possible Ways of 1 Seven classes of food (nutrients): Symptoms vision causes correction Nutrient Sources Function Deficiency disease Short- • Can see near • Lens is too Concave ek sightedness objects clearly thick lenses Carbohydrates Sugar, starch, glucose • Supply energy to the body Body lacks energy, marasmus • Cannot focus on • Eyeball is Proteins Milk, fish, eggs, chicken • For growth Stunted growth, kwashiorkor distant objects too long • Repair of body tissues he Long- • Can see distant • Lens is too Convex Fats Oil, ghee, margarine, butter • Keep the body warm Body lacks energy sightedness objects clearly thin lenses • Transport vitamins A, D, E and K • Cannot focus on • Eyeball is • Supply a lot of energy near objects too short rc Fibre (roughage) Fruits, vegetables, cereals • Helps peristalsis and removal of Constipation Astigmatism • See distorted • Irregular Cylindrical undigested food from the body images surface of lenses or the cornea through m Water Fruits, vegetables, drinking • Dissolves chemicals in the body Dehydration surgery water • Controls body temperatureWB Science F2 (Exp Note) 1st.indd 2 4/2/2009 5:48:17 PM
    • Page 3 Nutrient Sources Function Deficiency disease 2.3 Human Digestive System Vitamins Vitamin A Carrot, fish liver oil, green • For night vision • Night blindness 1 Digestion is the breakdown of large food u vegetables • Healthy skin • Skin infections molecules into smaller molecules that can be easily absorbed by the body. .a Vitamin B Milk, eggs, meat, cereals • Healthy nervous system • Beriberi 2 Digestion occurs in the alimentary canal (or • Formation of red blood cells • Anaemia gut): Vitamin C Citrus fruit, vegetables • Healing of wounds • Scurvy om • Resistance to diseases Mouth oesophagus stomach Vitamin D Made by our body in sunlight, • Strong bones and teeth • Rickets optic nerve small intestine duodenum also found in eggs, milk large intestine anus Vitamin E Nuts, vegetable oil, whole grains • For healthy reproduction system • Sterility t.c • Fights against diseases 3 Peristalsis is the contraction and relaxation of the muscles along the gut wall. Vitamin K Made in the human intestine, • Helps blood clotting and stops • Prolonged bleeding 4 Enzymes are substances which generally act as also found in green vegetables bleeding catalysts to speed up the chemical reactions in po Minerals Calcium Milk, cheese, green vegetables • Strong bones and teeth • Rickets our body. • Healthy muscles and nerve • Osteoporosis • Muscle cramps Oesophagus – Produces a wave-like action called peristalsis gs Sodium Table salt, cheese, meat • Controls body fluid • Muscular cramps – Peristalsis helps to push bolus into the stomach • Proper functioning of nerves Iron Meat, green vegetables, eggs • For the formation of haemoglobin • Anaemia Mouth Stomach – Physical digestion – Produces gastric juices in the red blood cells lo occurs – Gastric juice contains Iodine Seafood, iodised salt • For making hormones in the • Goitre – Starch is broken hydrochloric acid and down into maltose protease thyroid glands – Proteins are broken Phosphorus Meat, eggs, vegetables cheese, .b milk, • Strong bones and teeth • Stores energy • Rickets • Fatigue Liver down into polypeptides or peptones in Potassium Bananas, meat, nuts • Proper functioning of nerves • Paralysis Gall bladder Pancreas produces produces bile pancreatic juice 2 Food tests: 2 The energy requirement depends on the age, ek Nutrient Test Result body size, sex, occupation, physical activity, Large intestine Starch (a type of Blue-black climate and state of health of an individual. Iodine test 3 Calorific value (or energy value) is the amount of Rectum carbohydrate) colour energy released from one gram of a particular Anus Glucose (a type Benedict’s Brick-red he type of food. of carbohydrate) test precipitate Duodenum Lower part of small intestine Protein Millon’s test Red precipitate Class of food Energy value (kJ/g) – Receives bile from the gall – Secretes intestinal juice blader and pancreatic juice – Maltose is broken down Fat Emulsion test Milky solution rc Carbohydrates 17 – Starch is broken down into into glucose maltose – Polypeptides are broken 2.2 The Importance of a Balanced Diet Proteins 18 – Proteins are broken down into down into amino acids polypeptides – Fats are broken down into m 1 A balanced diet contains seven classes of food in Fats 39 – Fats are broken down into fatty acids and glycerol the right amount. fatty acids and glycerolWB Science F2 (Exp Note) 1st.indd 3 4/2/2009 5:48:18 PM
    • Page 4 2.4 Absorption of Digested Food 5 Plant kingdom can be divided into: 7 Classification of non-flowering plants: (a) flowering plants 1 Absorption is the diffusion of digested food from (b) non-flowering plants Non-flowering plants u the gut into the bloodstream. 6 Classification of flowering plants: 2 Absorption mainly happens in the small intestine. .a 3 Villi on the inner wall of small intestine help to Flowering plants Conifers Mosses Ferns Algae speed up the absorption. om 2.5 Reabsorption of Water and Defecation Monocotyledons Dicotyledons Examples: Examples: Examples: Examples: • Pine tree • Stag’s • Cup • Seeweed 1 Reabsorption happens in the large intestine. • Casuarina horn moss • Phytoplankton 2 Water, with dissolved minerals and vitamins are tree fern reabsorbed into our body. t.c 3 Defecation is the process of removing faeces from the body through the anus. Two CHAPTER 4 4 Difficulty in defecation is called constipation, One cotyledon which is caused by the lack of water and cotyledon Interdependence among Living po roughage in the diet. Organisms and the Environment A maize grain cut in A green bean (split 2.6 Healthy Eating Habits half into two) 4.1 Interdependence among Living Organisms 1 We should practice healthy eating habits to gs prevent diet-related diseases. Network- Key terms Description 2 We should eat a wide variety of foods according to the recommended amounts in the food pyramid. veined leaf Species Organisms with common characteristics lo which can breed among themselves to CHAPTER 3 Parallel-veined produce fertile offspring leaf Flower Biodiversity 3.1 Organisms and Their Classification .b Stem Stem Tap root Population Community A group of organisms of the same species which live in the same place Many types of populations living in Fibrous root in 1 Biodiversity (or biological diversity) refers to the the same place, interacting with one wide variety of organisms on earth. Example: Maize plant Example: Balsam another ek 2 Organisms are classified into groups called plant Habitat The place or area where an organisms kingdoms, such as animal and plant kingdoms. • Fibrous root system live and reproduce (a) vertebrates (animals with backbones) • Parallel-veined • Tap root system (b) invertebrates (animals without backbones) leaves • Network-veined Ecosystem The community of organisms living in he 4 Vertebrates are divided into five groups: • Non-woody and leaves the same habitat, together with the soft stems • Woody and hard non-living environment Vertebrate Characteristic • Other examples: stems Fish Slimy scales and fins Grass, orchid plant, • Other examples: Ecology The study of relationship between living rc Amphibians Exposed and moist skin sugar cane, paddy rubber tree, things and the environment Reptiles Hard dry scales rose shrub, bougainvillea, 1 A balanced ecosystem is created when there is Birds Feathers and wings m sunflower plant interdependence among living organisms and Mammals Hair or fur the environment.WB Science F2 (Exp Note) 1st.indd 4 4/2/2009 5:48:20 PM
    • Page 5 4.2 Interaction between Living Organisms 1 Biological control uses the prey-predator 4.5 Conservation and Preservation of Living relationship to control pests. Organisms u Type of interaction Description Examples 4.3 Food Web 1 Conservation is the wise use of natural resources Prey-predator • A predator is • Goat (prey) with the least disturbance to the ecosystem. .a an animal that and tiger Key terms Description 2 Preservation refers to the actions taken to hunts other (predator) maintain ecosystem in its balanced state. animals for food • Frog (prey) Producer Green plants which can produce 3 Some steps to conserve and preserve ecosystem: om • A prey is an and snake food through photosynthesis. animal hunted (predator) and killed by • Rat (prey) and Steps Purpose Consumer Animals which eat plants and other predators for owl (predator) animals Controlling To minimise destruction of habitats food Decomposer Organisms that break down dead pollution of animals and plants t.c Competition Intra-specific • Competition • Wolves animal and plant materials into Managing natural To protect animals and plants by competition between the compete with same species of each other simpler substances which can be resources the establishment of sanctuaries, organisms for food and used again by the producers. forest and wetland reserves po mate 1 A pyramid of numbers shows the number of Renewing natural To restore destroyed habitats Inter-specific • Competition • Crows and fox organisms at each stage of a food chain. resources due to logging, mining and competition between compete with overfishing organisms of each other for Number of gs Level 4 Managing forest To minimise deforestation and different species food organisms (tertiary consumer) decreases, illegal logging, and prevent forest Symbiosis Commensalism • Interaction • Remora fish Level 3 (secondary fires between two (commensal) Size of consumer) Passing of To monitor commercial hunting, lo organisms and shark organisms • The commensal (host) increases Level 2 (primary legislation of overfishing, and protect receives benefits consumer) wildlife protection endangered species Amount from the host • The host is not harmed nor received any .b of energy decreases Level 1 (producer) Educating the public To increase public awareness on the importance of conservation and preservation of ecosystem in benefit 4.4 Photosynthesis 4 Technology which can help in the conservation Mutualism • An interaction • Fungi (provide and preservation of living organisms: ek which benefits shelter 1 Photosynthesis is a process of making food by both organisms to algae) green plants. and algae Technology Importance 2 Requirements for photosynthesis: (produce food (a) Water Tissue culture To increase the population of he for fungi and (b) Carbon dioxide (cloning endangered species itself) (c) Chlorophyll technology) Parasitism • A parasite • Tapeworm (d) Sunlight benefits by (parasite) Artificial To prevent the extinction of 3 Products of photosynthesis: rc living in or on living in insemination the endangered species (a) Oxygen the host the human (b) Glucose Satellite imaging To detect fires in the ecosystem • The host is intestine Chlorophyll and prevent the destruction m harmed by the (host) Water + Carbon dioxide Oxygen + Glucose of natural habitats parasites SunlightWB Science F2 (Exp Note) 1st.indd 5 4/2/2009 5:48:21 PM
    • Page 6 4.6 Role of Humans in Maintaining the Balance of 2 A water molecule contains two atoms of 4 Similarities between evaporation and boiling: Nature hydrogen and one atom of oxygen. (a) both involve the change of state from liquid 3 Electrolysis is a method of breaking down water to gas (steam) u 1 Examples of human activities: using electricity. (b) both processes absorb heat (a) Deforestation 4 During electrolysis, oxygen gas is released at .a (b) Land overuse due to intensive farming the anode and hydrogen gas is released at the 5.4 Solution and Solubility (c) Overfishing and overhunting cathode. (d) Industrialisation om Key terms Definition (e) Poor solid waste management 5.3 Evaporation of Water 2 The effects of human activities: Solution A product formed when a solute (a) Global warming 1 Evaporation is the process by which a liquid dissolves in a solvent (b) Destruction of habitats changes into water vapour. 2 Factors affecting the rate of evaporation of Solute A substance which dissolved in a (c) Extinction of species t.c water: liquid (d) Soil erosion (e) Pollution of air, water and soil Solvent A liquid which dissolves a substance Factors Explanation Dilute solution A solution which has very little solute po Temperature The higher the temperature of the in it CHAPTER 5 of the surrounding, the higher the rate of Concentrated A solution which has a lot of solute Water and Solution surrounding evaporation of water solution in it gs Surface area The larger the surface area of water, the Saturated A solution which has maximum of water higher the rate of its evaporation solution amount of solute in it 5.1 Physical Characteristics of Water Humidity The lower the humidity, the higher the Suspension Mixtures which contains insoluble 1 Impurities can change the physical characteristics rate of evaporation of water lo of water. substances Movement Air movement increases the rate of 1 Differences between a solution and a of air evaporation suspension: Freezing point = 0° Boiling point = 100°C Expands upon freezing .b 3 Differences between evaporation and boiling: Solution Suspension Evaporation Boiling in Contains dissolved Contains insoluble A slow process A fast process substances substances Physical ek Odourless, Occurs at the surface of Occurs throughout liquid Homogeneous (uniform Non-homogeneous characteristics Density tasteless, liquid in colour and transparent (opaque or cloudy of pure water = 1 g/cm3 at 4°C colourless appearance) appearance) Occurs at all temperatures Occurs at the boiling point he (below the boiling point of liquid Light can pass Light cannot pass of liquid) through it through it Poor electrical Poor thermal conductor conductor Nothing visible observed Air bubbles observed No residue is formed Residue is collected when filtered when filtered rc Affected by humidity, Affected by air pressure, temperature of presence of impurities, rate 5.2 Composition of Water surrounding, surface of heating and volume of 2 Solubility is the maximum amount of a solute in m 1 Water is made up of hydrogen and oxygen area of water and air liquid grams that will dissolve in 100 g of solvent at a elements. movement certain temperature.WB Science F2 (Exp Note) 1st.indd 6 4/2/2009 5:48:22 PM
    • Page 7 3 Factors affecting the solubility of a solute: 3 In neutralisation, an acid reacts with an alkali to 5.8 Preservation of Water Quality produce to produce a salt solution. Factors Explanation 1 Causes and effects of water pollution: u Acid + Alkali Salt + Water Nature of Different solutes have different solubility in Causes Effects .a solute the same solvent 5.6 Water Purification Silt (mud and sand) Water becomes muddy and The solubility of a solute varies with Temperature rivers become shallower temperature Water purification om Purpose method 4 The rate of dissolving means the time taken by a Domestic waste (garbage Contains harmful micro- solute to dissolve completely in a liquid. Filtration To separate solid particles such as clay, and untreated sewage from organisms which can cause 5 Factors affecting the rate of dissolving: sand and other insoluble particles homes) cholera and typhoid Factors Explanation Boiling To kill micro-organisms with heat energy t.c Agricultural waste (pesticides Causes rapid growth of algae Temperature The higher the temperature of the solvent, Chlorination To kill micro-organisms with chlorine and fertilisers) and therefore reduces oxygen the higher the rate of dissolving level in the water Distillation To remove dissolved substances, insoluble particles and to kill micro-organisms po Rate of stirring The higher the rate of stirring, the higher the rate of dissolving Oil spillage (from tankers in Kills aquatic life and seabirds Ultraviolet (UV) To kill micro-organisms with ultraviolet the sea) Size of solute The smaller the size of solute particles, the treatment rays particles higher the rate of dissolving Industrial waste (chemical Poisons aquatic life and cause gs 6 Water is known as the universal solvent. It can 5.7 Water Supply System and radioactive wastes from skin cancer dissolve most substances. factories) 7 Organic solvents can also be used to dissolve 1 Process of water treatment in a water treatment lo some solutes. plant: 2 Ways to control water pollution: 8 Characteristics of organic solvents: Screening Aeration Coagulation Ways of controlling (a) volatile (evaporate easily) Explanation (b) carcinogenic (likely to cause cancer) (c) toxic (poisonous to the living cells) (d) flammable (easy to catch on fire) .b Filtration Sedimentation Chlorination and fluoridation water pollution Prevention • Planning of proper sewage system in in the new residential areas Process of water • Treating wastewater before Purpose 5.5 Acid and Alkali treatment discharging into the public sewage ek Screening To remove large objects (fish, branches and system 1 Properties of acid and alkali: rubbish) • Avoid dumping rubbish or waste into Acid Alkali Aeration To dissolve oxygen and to remove unpleasant the water smell and taste he • Corrosive • Corrosive Coagulation • Alum – To make small particles stick Enforcement • Imposing fines and punishment for • Turns moist blue litmus • Turns moist red litmus paper paper red blue together to form larger and heavier lumps those who dump untreated water, • Has a pH less than 7 • Has pH greater than 7 • Lime – To reduce the acidity of water garbage and chemical wastes into • Tastes sour • Tastes bitter and feels soapy rivers rc Sedimentation To settle out and remove large lumps • Reacts with most metals to product hydrogen gas Filtration To remove the remaining solid particles Monitoring • Raw sewage should be treated and turned into safe effluent before m 2 Both acid and alkali need water to show their Chlorination and • Chlorine – To kill harmful micro-organisms fluoridation • Fluoride – To prevent dental decay discharging into the sewage system properties.WB Science F2 (Exp Note) 1st.indd 7 4/2/2009 5:48:23 PM
    • Page 8 CHAPTER 6 Factor Relationship Device Explanation Air Pressure Volume Air pressure increases when volume Drinking straw (a) Air sucked from u decreases straw causes low pressure in the .a 6.1 Air Pressure Temperature Air pressure increases when Atmospheric pressure pushes the water straw. temperature increases 1 Air pressure exists when the air around us presses up the straw (b) Air pressure pushes liquid into the straw om on the surfaces of the objects. Water 2 Activities to show that air exerts pressure: 6.2 Application of the Principle of Air Pressure Drinking straw and the mouth. (a) Device Explanation Gas Under High Pressure Water Syringe (a) When the piston is t.c pulled up, a lower 1 Gases can be compressed into liquid under high Cardboard Piston pressure is created pressure, and stored in gas tanks. pulled 2 Safety measures when using gas under high upwards inside the barrel of the syringe. pressure: When the hand is released, the water in po (b) The air pressure (a) Keep aerosol cans away from the sources the glass does not flow out because air of heat, such as open flames, sunlight and Atmospheric outside forces liquid pressure presses on the under surface of the Nozzle pressure heaters. High temperature may cause an cardboard. forces the into the barrel of Liquid liquid into the syringe. explosion. gs (b) (b) Do not dispose aerosol cans into incinerators the barrel Steam as they may explode. Steam Cover condensed Siphon (a) A lower pressure is Cold (c) Do not dent or puncture aerosol cans as they Steam water Reduced pressure developed in the may explode. lo Atmospheric Atmospheric when water presure tube. (d) Gas tanks must be kept in an open, cool and Hot pressure pushes flows out of tube water water into tube (b) The air pressure good ventilated place. outside pushes (e) Always place the gas tank upright to prevent Heat When cold water is poured over a heated tin, the tin is crushed and collapses. .b Tube filled with water water into the tube. gas from leaking. (f) Turn off the valve each time after use. (g) Perform regular gas leakage checks to ensure in 3 The kinetic theory of gases can be used to explain there are no leakages. the existence of air pressure. Spraying pump (a) When the piston ek 4 According to the kinetic theory of gases, Reduced is pushed, the air (a) a gas has many particles which are far apart Air is compressed presure inside the barrel is CHAPTER 7 and pressure when air from each other increases when comes out at compressed, pressure Dynamics (b) these gas particles move freely and randomly, Piston piston is pushed high speed increases and pushes he in all directions Fine droplets air out of nozzle at (c) these gas particles continuously collide with high speed. 7.1 Force the walls of the container and bounce back Push (b) The pressure reduces Liquid 1 A force is a push or a pull acting upon an object. (d) a force is exerted by the gas particles on the when air comes out rc Atmospheric pressure pushes 2 Effects of forces: walls of the container liquid up the tube at high speed. (a) Can change shape (e) the force produces a pressure on the walls of (c) Air pressure pushes (b) Can change position the container liquid up and out as m (c) Can change direction 5 Factors affecting air pressure: fine droplets. (d) Can change speed (increases or reduces speed)WB Science F2 (Exp Note) 1st.indd 8 4/2/2009 5:48:24 PM
    • Page 9 3 Different types of forces: 5 Methods to reduce friction: CHAPTER 8 Type Description Method Application Support and Movement u Gravitational The force that causes objects to fall to the Roller or ball bearings In automobiles and machines force ground .a Magnetic force The force that acts on magnetic materials at Layer of air cushion Hovercrafts 8.1 Support Systems in Animals a distance Lubricants (grease, oil) Moving gears, engine pistons, Electrostatic The force that is caused by charged door hinges Support System Description Examples of animals om force materials Wheels Roller blades, trolleys, sofas, Exoskeleton An outer skeleton Grasshoppers, Frictional force The force that is caused by surfaces in (in invertebrates) which is made of cockroaches, pianos, wheelchairs contact hard materials prawns, crabs Electromagnetic The force that is produced by running (such as chitin) force electricity through a magnetic material t.c 7.4 Application of Work Endoskeleton An internal Humans, elephants, (in vertebrates) skeleton which is horses, whales 7.2 Measurement of Force 1 Work is done when a force is exerted to move an made of bones and object in the same direction as the application of muscle attachments 1 The SI unit for force is Newton (Symbol: N). po the force. 2 Spring balance (or Newton balance) can be used Hydrostatic Liquid (mainly Earthworms, sea to measure force. Work (J) = Force (N) × Distance (m) skeleton (in water) which anemones, starfish invertebrates) supports and 7.3 Application of Frictional Force maintains body 2 The unit for work is joule (J). gs 1 Frictional force has a magnitude and a direction. 3 1 joule of work is done when 1 newton of force shape and turgidity 2 The direction of the frictional force is parallel moves a distance of 1 metre, in the direction of to the surface and in the opposite direction of the force. 1 Aquatic vertebrates have smaller endoskeletons lo motion. compared to land vertebrates. 3 Factors affecting magnitude of frictional force: 7.5 Application of Power 2 Aquatic vertebrates gain support from Factor Description buoyancy. Type of surface The rougher the two surfaces are, the greater the frictional force between them .b 1 Power is the rate of doing work. Work done (J) 3 Buoyancy is the force from water that enables objects to float. Power (W) = ––––––––––––––– in Weight of object The heavier the object, the greater the 8.2 Support Systems in Plants Time taken (s) frictional force 4 Advantages and disadvantages of friction: Support system Description Examples of plants ek 2 The unit for power is watt (W) or joule per second Advantages Disadvantages (J s–1). Buttress roots Large roots which Rain tree, flame of form the base of the the forest • Provides a good grip and • Wears off surfaces in stem to provide extra prevents objects from contact, such as shoe soles 7.6 Importance of Force in Life he support slipping and tyres 1 Our daily activities cannot function without • Provides resistance to • Produces unwanted heat Prop roots Roots which grow Banyan tree, maize force. from the branches or motion, so that moving that can damage surfaces 2 Importance of force: the nodes of the stem • Produces noise and causes rc objects can stop (a) frictional force enables us to hold all objects • Produces heat, for example noise pollution (b) magnetic force and electrical force make the Clasping roots Roots which enable Orchids, money striking a matchstick • Wastes energy as more machines work the plant to climb by plant, pepper growing around and plant m energy is needed to (c) gravitational force allows objects to stay on overcome friction gripping its support the groundWB Science F2 (Exp Note) 1st.indd 9 4/2/2009 5:48:25 PM
    • Page 10 2 A stable object does not topple easily. Support system Description Examples of plants Type of 3 The centre of gravity of an object is the point at Feature Use Examples lever Tendrils Coiled structures that Cucumber, garden which the whole weight of the object seems to u develop from the stem pea, pumpkin concentrate at. or leaf. They wrap 4 The centre of gravity of an object is also the Second- L between F and E To produce • Nutcracker .a around the support point of equilibrium of the object. class a large • Paper cutter E and help the plants to lever force from a • Wheelbarrow 5 The centre of gravity of objects can be determined F climb small force • Bottle opener using a plumb line. om Thorns Modified braches that Bougainvillea 6 Factors that affect the stability of an object: L cannot be removed easily from the stem Factor Description Prickles The outgrowth of the Roses Position of the The lower the centre of gravity of an object, Third- E between F and L To produce • Broom t.c epidermis which can centre of gravity the more stable is the object class a large • Ice tongs be easily removed E Base area The larger the base area of an object, the lever movement • Fishing rod from the stem F more stable is the object from a small • Human arm Air sacs Provide buoyancy and Brown alga movement L po help plants to stay 9.2 Importance of Stability afloat in water 1 Stability is important to ensure that an object Stilt roots Roots which develop Mangrove tree does not topple over. from the main stem of 4 The moment of a force refers to the turning gs 2 Stability of an object can be increased by: the trees effect of a force. (a) lowering its centre of gravity (b) increasing its base area 8.3 Appreciating the Support System in Living Moment of a force (N m) lo Organisms = Force (N) × Perpendicular distance from the 1 Physically disabled persons, aged people, CHAPTER 10 pivot to the force (m) injured persons use various ambulatory aids for .b additional support. Simple Machine 5 Moments in a lever describe the opposing 2 Examples of ambulatory aids are: 10.1 Levers moments produced by the effort and the load in (a) Cane (walking stick) in a lever. (b) Crutches 1 Levers are simple machines. 6 When two opposing moments are balanced: (c) Walking frame 2 A lever consists of a rigid bar that turns freely ek 3 Beached and stranded whales will die because about a fixed point (called fulcrum, F), when a their internal organs will be crushed by their force (called effort, E) is applied to overcome the Load (N) × Distance of load from the fulcrum (m) own weight. resistance force (called load, L). = Effort (m) × Distance of the effort from the 3 There are three classes of levers. fulcrum (m) he Type of CHAPTER 9 lever Feature Use Examples Stability First- F between E and L To produce • Pliers rc class a large • Scissors 10.2 Appreciating the Innovative Efforts in the E Design of Machines to Simplify Work 9.1 Stability lever F force from a • Crowbar small force • Claw hammer 1 Levers can be used to design machines that help m 1 The stability of an object refers to its ability to L to simplify our work. maintain its original position.WB Science F2 (Exp Note) 1st.indd 10 4/2/2009 5:48:26 PM