gr7 - Sources of energy & potential &kinetic energy (3).pdf

Energy and Change An everyday example of a simple mechanical system is using a pair of sciss9rs to cut paper. In Figure 10.9, the water wheel is turned by the energy tho~ comes from falling water. In an electrical system such as the one in Figure 10.10, chemical potential energy in the cell (batter...

Energy and Change An everyday example of a simple mechanical system is using a pair of sciss9rs to cut paper. In Figure 10.9, the water wheel is turned by the energy tho~ comes from falling water. In an electrical system such as the one in Figure 10.10, chemical potential energy in the cell (battery) will cause an electric . current to flow, which in turn causes the bulb to shine. Figure 10.q A waterwheel Figure 10.10 • A simple electrical circuit Mechanical systems are also found in sporting activities. A cricket bat striking a cricket ball is a begin, a bowler bowls the cricket ball at good example. the batsman-. Potential energy in the arm muscles of the bowler is transferred to the cricket ball as kinetic energy and the ball travels through the air. The batsman hits the ' energy in the muscles ball with his bat. Again, potential ' . of the batsman is transferred to the cricket bat as kinetic energy. The bat strikes the ball, resulting in a change in di.rection and speed. To ' Figure 10.11 A batsman striking a cricket ball The energy transfers in this example can be shown in flow diagrams. bowler (potential energy) INPUT . ball speeds . towards batsman (kinetic energy) OUTPUT · -throws·cricket ball · PROCESS _ .., ., r batsman (potential energy) hits the cricket ball PROCESS . INPUT ball speeds towards the boundary (kinetic energy) . . OUTPUT Figure t0.12 Energy transfers in cricket I, nl nnd ldnAtiC eneraU I' Energy and Change 2. -..... Where does the initial ·energy in this system come from? Where does the energy go to? What did you observe as a result of this change in energy? Explain how the ener~y is transferred in this . system by using a flow diagram ... . Write a conclusion using your results. Suggest how the result~ could be made mo~e accurat~. Draw a bar graph to show the results you . obtained from "' ' 3. 4. 5. I • - 6. '1. 8. . . the investigation. . .' Lesson 2 . Potential and kinetic energy in therm al systems · . thermal: refers to heat ' . One substance is described as being warmer than another substance because it has more thermal energy. The warmer a substanc~ is, the greater kinetic energy its particles have. lace when heat energy is transferred Thermal tra_nsfer takes p_ fro~ one area or object to another. Heat energy will move · from a warmer area or object to a · cooler one, until it is evenly distributed. The more heat energy an object has, the hotter it feels to touch and the · faster its particles move. There is more kinetic energy in warmer areas or objects than colder areas or objects than colder areas or objects. Figure 10.14 A kettle used to boil water Heat transfers take place in many household appliances such as geysers, stoves and kettles. • Topic 10 P~tential and kinetic energ_y 0 All of these appliances have an electrical element that h~ats up and so warms the water or air that is inside them. Below is a thermal transfer flow diagram for an electric kettle. ... - electricity supply to kettle (input) '-. ~ ' r "' / '-. element heats up due to thermal (process) transfftr . 'I r water in kettle begins to boil (output) ... ~ ~ ./ '-. Figure 10.15 Thermal transfer flow diagram for electric kettle The hot water from the kettle can be used to make tea. Once the tea is poured into a cup, the liquid will begin to cool. The tea is warmer than the surrounding air so heat energy will move from the tea to the surrounding air. The ·tea will lose heat. ~....,. ~---- -• v.-=~!'f't""('\ ;. . "' "1- ~ '• ;: r .. '_· ~ • . . ._ ~- i·~-----. • •• ~- I • .. • I • • ~•, ·_ ·::.·, ,~·- - } ~- ,- -----.... ........:...~-~~ .... .~ ..~ .:_ Figure 10.16 Hot tea will lose heat to cooler surroundings. Cool fact: Thermal imaging camer as can be used to diagnose injuries in people. The image of the heat coming off of various parts of a person's body allows doctor s to see where there might be injuries withou t them having to do any invasive tests. Figure 10.17 A thermal image of a human Lesson 3 . . Poten tial energ y and l<inetic energy in .· electr ical syste ms ....,. is a system . It is formed when An electric.al circuit . . items such as cells or batteri es, switche s and bulbs are joined up using insulat ed connec ting wires. An -electric al circuit forms a system . An examp le of an electric al system is shown in switch- +---~.: - cell Figure 10.19. ~n Figure 10.19, the source of the electric al energy is the cell. The electric al energy that the cell ge'n erates create s a flow of charge d particle s that travel around the circuit. Finally there is an output which results in the oulb glowing. This can be summa rised in a flow diagra m (Figure 10.20). a• Topic 10 Potential and kinetic ·energy . light bulb Figure 10.1q A simple electrical system electric current sta rts to flow (prdcess) pot ent ial ene rgy in cel l (inp ut) Fig ure 10.2 0 An elec tric al circ uit is a sys tem ...... light bulb glows (output) l Le ss on 4 gy in bio log ica l er en c eti kin d an gy er en l tia ten Po s ys te ms _ / _ y sys tem s. Or ga nis ms erg en ate cre to le ab are s ism an org Living l po ten tia l en erg y in the ir sto re food an d so the y have chemica nt by tra ns for mi ng the bodies. They can use thi s for moveme po ten tia l energy int o kinetic energy. Consider a horse as an example. The horse ea ts grass. The grass contains ca rbo hy dra tes tha t contain po ten tia l energy. This chemical potential energy wa s formed using the Sun's light energy. When the horse ea ts grass, some of the energy is used to maintain the horse's body, some is stored in the horse's bo dy and the rest is used by the horse to move and do work. The energy in the horse's muscles can be pu t to use in several ways. In Figure 10.22 a) the energy is being used for pulling a ca rt. Figure 10.21 A hor se gra zin g a rider (Figure 10.22b). . rry ca to d use be o als can rgy en~ e Th I & • Topic 10 Potential and kinetic energy Figure 10.22 a) A horse-drawn cart used for transport b) A Basuto pony and its riders ., Cool fact: Before motor cars were invented, humans were dependent on horses for transport. The power of a motor car engine is still described in terms of 'horsepower'. Food chains and energy producers: . organisms like plants that are able to convert energy from the Sun into chemical energy consumers: animals that eat plants and other animals A food chain shows how energy is passed from one living organism to another (Figure 10.22). Plants are producers and trap light energy from the Sun. They change it to chemica1 potential energy during photosynthesis. Animals are consumers. Animals get energy·from plants when they eat them. Animals can also eat other animals. In this way energy is passed from one living organism to another in a Figure 10.23 A food chain shows · food chain. how energy is passed from one organism to another. ft 1. 2. 3. 4. 5. 6. I I• Where does the initialen ergy in a biological · © _ system come from? . . . Individual . Where is the energy transferred to? : · .What energy changes tak~ place when a·· · ·. ~ .· . ·· . · ·: . , horse eats grass? he Draw a flow diaQram, with arrows, to show t _ energy transfer in this-system. ·.·.' ·. . !' .,. What is a food chain? :. · Give an example of food chai~ and use it to ~xplai11 how energy is transferred through it. :j Lesso n 5 Law of conse rvation of energy The law of conservation of energy When energy is used, it does not simply disappear. The energy is changed from one form of energy into another. This is stated in the law of conservation of energy. Conservation of energy does not mean saving energy. The law states that energy can neither be created nor destroyed, but it can be converted from one form to another. law of . cdnservatlon of energy: a law that states : that energy in a system is never lost but simply · converted to a · different form energy transformation: when energy changes from one form to another, for example . . potential enerQY ·to kinetic energy or vice versa Fuel such as petrol is needed to provide the energy for a car to move. Petrol contains chemical potential energy. The petrol is burnt in the engine and provides the energy that moves the mechanical parts of the engine. This is called mechanical kinetic energy. Some of the energy fr.om the petrol is given off as heat. This heat energy is said to be 'lost', because it is not useable in the system. However, the energy is no~ lo~t as such., but has been converted from one form to here has been an energy transformation . another. We say that t_ G • Topic 10 Potential and kinetic ene~gy • • • In Le sso n 3 yo u bu ilt an e1ect nca l c1rcu1t wit h a buzzer in it l energy in the cell wa~ In su ch a sys tem , che mic al po ten tia was in tur n converted to co nv ert ~d to ele ctr ica l energy, which the buzzer rang. This shows me cha nic al an d sou nd energy when . form into another. tha t en erg y is tra nsf orm ed from one ms and energy transfer Energy syste_ energy system: . nt energy thi s top ic you ha ve learnt ab ou t differe In . a network of store and release energy. The pa rts can tem sys A . ms ste sy s different source rk together. This of a sys tem are interconnected and wo of energy tha t . system will aff ect inte rac t wit h one me an s tha t a change in one pa rt of the another sucti,,_~i~~/-·~· sys tem..In a simple electrical system, the of rts pa all energy y 3, adding extra cells to tf:le ·· ' ,_ ivit act al ctic Pra in e on the as the transfer: in the system. This passing of cir cui t increases the amount of energy uit glow brighter. If energy from one ma kes a ligh t bulb att ach ed to the circ will pa,:t of a sys tem d light bulb is added in series;-th e lights on· sec a r, eve how to another • be cam e dimmer. s when energy is passed In a sys tem , energy transfer happen system to another when on or transferred from one pa rt of the bring ab ou t a change. In the pa rts interact. This interaction will above, the extra cell had the example of an electric circuit given {and therefore transformed) po ten tial energy tha t was transferred and resulted in the·light int o an electric current {kinetic energy) tems diagram to the bulb ge ttin g brighter. If you apply a sys r system would look like example of the electrical circuit, then you the one in Figure 10.24. ext ra cell . _ in circ uit light bul b glows brig hte r increased cur ren t in circ uit ene rgy sys Figure 10.24 Diagram of an ele ctri cal tem · rgy was sto r~ in the In the system shown, the potential ene into kinetic energy when it electrical cell. It wa s then transformed current in the circuit. caused an increased flow of electrical energy : . • Topic 10 Potential and kinetic 0 The change brought about by this system was that the light bulb became brighter. Energy transf~r in an electric motor A good example of converting energy in one system to energy in another can be found in electric motors. Electric motors are used in many everyday appliances. The electrical system in a motor transfers electrical energy from a battery tq the mechanical parts of the motor. When the battery is connected, an electric current flows along the moving parts in the motor. 'The current produces a force that turns the coil. Figure 10.25 A simple electric motor Energy _transfers in a motor involve chemical energy, electrical energy and kinetic energy. You will learn about electric motors in more detail in Grade 8. Th·e picture below shows a toy airplane that is , powered by a rubb~r band. When the propeller is · turned by hand, it twists 't he rubber band. When · the propeller is released, it spins and the plane flies. 1. What is the inpu_t into· .. : : the system? II ! f 1 d1 " vldual . 2.. What is the output from the system? . -■ l 3. What is the process in . · ·Figure 1D.26An aeroplane which i this system? is profJ':lled by a rubber band j 4. What energy transfers have taken place? .. . . . .· . Explain how the energy that was put into the system has been used. _ . 1 6~ · Draw an energy flow diagram for the system shown l here · · · · · · ·'I! I I ~i . I' I ? • ..... _ • • ~ • • • : I • • ' • ~ - - - - ~ - - ~-•••. - • - - ~ - . . . . _ , _ _ ~ - • Topic 10 Potential and kineti~ energy • - - ~ . • ·- •L ~ W_ _ _ _, • ~- : __;_./ Summa ry -_ • • • • • • • Energy is the ability to do work. Energy is measure d in Joules. Almost all the energy on Earth comes from the Sun . There are many forms of energy: chemical energy, light energy, electrical energy, sound energy, nuclear energy, heat energy, potential energy and movement , o~.kinetic energy. . ~ Potential energy is stored energy that is available for later use. · Kinetic energy is the energy of movemen t . Energy may be transform ed from one form to another. The law of c0nservatior1 of energy states that energy · · caA neither be created nor destroyed , but it can be converte d from one form to another. An energy system is a network of different sources of energy that interact with one an0ther to bring about · a change. .. Different types of energy systems include mechenie al, thermal, electrical and biologica l. Energy may be transferre d from one ·object to another or from one system to another, as in e motor;. 4 • • •