Chapter 5: Using energy

Transcription

1 Chapter 5: Using energy Unit The joule (J) is the unit for measuring energy. 2 Students ould state any five from: kineti, sound, heat, eletrial, light, nulear, gravitational potential, hemial, elasti potential. 3 a kineti energy: in a moving ojet d e sound energy: in virating air partiles elasti potential energy: in a strethed or squashed spring gravitational potential energy: in ojets positioned aove the ground light energy: released from glow-worms 4 The energy in food is usually stated in kilojoules rather than joules eause one joule is a very small amount of energy. 5 Sound is produed y a virating ojet, suh as the string of a guitar or the prong of a tuning fork. In this way, sound is a form of kineti energy. 6 Petrol, kerosene and oil all possess hemial energy. 7 Student answers. Some examples are: ar rashing into an ojet, a golf all hitting a tree, the effets of a ylone, two people running and rashing into eah other, tripping over while running. 8 a 3 megajoules = J = J 7500 kilojoules = J = J 9 a joules = 2.5 megajoules 5000 kilojoules = J = J = 5 MJ 10 a hemial energy elasti potential energy Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 1

2 11 Chemial energy from food an e used y your ody to produe: growth (forming new moleules and storing energy) sound energy (talking, singing) kineti energy (movement) heat energy (ody warmth) 12 a heat energy d e f kineti energy hemial energy kineti energy hemial energy gravitational potential energy 13 a Daning for an hour, Ben uses: 30 kj 60 = 1800 kj of energy. One serving of this ereal with whole milk has an energy ontent of 930 kj. This means Ben would need to eat almost two serves to supply the energy for his hour of daning. When Ben danes, kineti energy, sound energy and heat energy are present. 14 Note that it is assumed that all ojets are on the ground exept where speifially stated otherwise. a d e f g h i hemial elasti potential hemial gravitational hemial hemial hemial gravitational hemial Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 2

3 j elasti 15 Many orret answers are possile, as long as the mass lifted (in kilograms) multiplied y the height lifted (in entimetres) equals 100. Two examples are: She ould lift a 20 kg ag of onions 5 m off the ground. She ould lift a 5 kg ag 20 m. 16 i Glass A, all A and ar A all have more energy than their pair. ii Eah glass has the same amount of water, ut glass A is hotter and so has more heat energy. Ball A has more energy than all B eause it is higher and so has more gravitational potential energy. Car A has more energy than ar B eause it is moving faster and so has more kineti energy. Unit There are many possile responses that involve energy transfer. For example, heat from a gas heater warming you up; kineti energy transferred from a person s leg to a footall. 2 A solar ell onverts light energy into eletrial energy. 3 a listening to an ipod: heat energy playing riket: heat and sound energy 4 a false true false 5 hemial energy 6 a An energy transformation refers to one form of energy hanging into another form of energy. For example, when a ranh falls from a tree, its gravitational potential energy is transformed into kineti energy. Eletrial energy is transformed into kineti energy of water partiles, whih is heat energy. This heat energy is transferred to the grains of rie as they ook. 7 a The Law of Conservation of Energy states that energy an never e reated or destroyed, ut an only e onverted from one form to another. The law means that energy an e onverted from one form into another, Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 3

4 suh as from gravitational potential energy into kineti energy as an ojet falls, ut annot e reated from nothing. Similarly, energy annot disappear. It is always onverted into other forms. For example, a all rolling along the ground eventually stops eause its kineti energy is onverted into heat energy as a result of frition. 8 Any ojet that moves (provided it is not in deep spae) moves against another sustane. It may have wheels that roll along the ground, or engine parts that move in oil, or it may move through air partiles. Regardless of the sustane that it is in ontat with, some frition will exist and heat energy will e produed. 9 Engine effiieny is the output of useful energy output ompared to the input of energy. This is usually expressed as a perentage. 10 Any heat losses produed y a devie will inrease the input of energy into the devie needed to get useful work done. (Unless the devie is a heater.) 11 The proess of onverting a fossil fuel suh as oal into household eletriity is very ineffiient eause heat energy is lost at every stage of the proess. Refer to Figure a From most to least effiient: steam engine, diesel engine, jet turine, petrol engine If 100 MJ of energy is input into the jet engine, 30% of this energy, or 30 MJ will e onverted to useful energy. 75% of energy is wasted in a typial petrol engine. 13 a The soure of this energy is the hemial energy that was ontained in the food that you have eaten (whih is onverted into kineti energy through your musles), and also gravitational potential energy if you are going downhill. Types of energy that are produed inlude kineti energy, sound energy and heat energy. 14 a ii d e i and v iv i and v iii Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 4

5 15 a The useful energy output is the kineti energy produed. Perentage energy effiieny = (useful energy output energy input) 100 = = 20% This means that 20% of energy input is onverted into a useful form of energy output. 16 a Sound energy produed = 2000 J ( ) J = 800 J Perentage energy effiieny = (useful energy output energy input) 100 = = 40% 17 a heat and sound energy The radiator ontains a liquid that asors some of the unwanted heat energy that is produed y the engine, and transfers the heat energy to the air. This makes the engine muh less likely to overheat. 18 When an ojet falls to the ground, all of its gravitational potential energy is onverted into kineti energy until the moment it hits the ground. An apple falling from the top of an apple tree has more gravitational potential energy than an apple falling from a lower part of the tree. So the apple from the top of the tree will have more kineti energy when it hits the ground. 19 a eletrial energy sound energy + heat energy hemial energy heat energy + sound energy + light energy gravitational potential energy kineti energy + sound energy + heat energy 20 kineti energy (of wind) eletrial energy kineti energy (of fan inside vauum leaner) + heat energy + sound energy Unit Many possile responses. Some examples are: turn off applianes and lights when they are not eing used; turn applianes off at the wall; use more energyeffiient applianes; re-use items rather than uying new ones; redue the use of private ars; redue the numer of flights; have shorter showers. 2 Any new household refrigerator, freezer, television, washing mahine, lothes dryer, single-phase air onditioner and any dishwasher sold in Australia. Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 5

6 3 Heat flows from regions of higher temperature to regions of lower temperature. 4 The Wright rothers ahieved the earliest reord of powered, heavier than air ontrolled flight in Compat fluoresent gloes are muh more energy effiient. 6 The energy rating lael shown in Figure shows four stars. This tells a onsumer that this appliane has a good level of energy effiieny, ut they should ompare ratings of similar applianes to see if there is a more effiient model in their prie range. 7 There are many possile responses. Some examples are: Floor insulation traps heat and saves on heating osts. The 6-star reverse yle air onditioning system is very energy effiient and will use less energy than other models. Eaves over the windows provide shading that redues ooling osts. Pool lanket traps heat in the pool, reduing heating osts. Compat fluoresent gloes are energy effiient ompared to inandesent gloes. Gas-oosted solar hot water system maximises the use of solar energy, whih redues gas use. North-faing aspet allows more solar energy to e olleted for heating water and produing eletriity, and makes the house warmer in winter whih uts heating osts. 8 Adding insulation to a house and sealing up gaps redues the heat exhange etween the inside and the outside of the house. This makes the heating used (or ooling used) more effetive and saves energy. 9 Regenerative raking stores some of the ar s kineti energy while raking and uses this to harge an eletri motor. This means that less energy needs to e used to make the ar run, whih inreases its energy effiieny. 10 To have wide use in the future, organi photovoltais need to e more effiient than they urrently are, otherwise the ost of produing them will not e worth the eletriity generated. 11 A dry washing mahine ould save energy ompared to a regular washing Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 6

7 mahine eause it does not need pumps to fill the mahine with water, or heating elements to heat the water. 12 Heat energy flows from regions of higher temperature to regions of lower temperature, so heat will flow from you hand (warmer) to the glass (ooler). 13 The odies of airraft needed to eome enlosed in order to redue the drag fore of frition that ats on them as they travel through the air. 14 The energy rating lael system was set up in this way, eause applianes are eoming more effiient every year. If the most effiient devies already had a 6 star rating in the first year of laelling then there would e no way to show improvement. 15 A 100% effiient ar would need very little fuel. It would e silent while eing driven, and the engine would not get hot. 16 Student responses should inlude all dates and events shown on pages 195 and 196 of the student ook, although the 400 BCE information ould e left out to avoid too muh lank spae in the timeline. 17 Student responses will depend on the appliane hosen. Chapter review 1 Stored energy is also alled potential energy. 2 Four types of stored energy are: gravitational potential energy, hemial energy, nulear energy and elasti potential energy. 3 Photosynthesis is the proess in whih green plants onvert sunlight to hemial energy. 4 A solar (or photovoltai) ell. 5 Many answers are possile. 6 You ody still needs energy while you are asleep to allow your heart to eat, your lungs, rain and other vital organs to funtion, and all of the other hemial and iologial proesses that happen all the time in your ody to ontinue. 7 An Energy Rating Lael assists onsumers y allowing them to ompare different models of the same type of appliane (suh as a refrigerator or dishwasher) to see whih offers the greatest energy effiieny. Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 7

8 8 Many answers are possile. Sample answers are: Kineti: push something over, suh as a owling all knoking a pin down Light: produe eletriity using a solar ell Heat: ook an egg in a frying pan Eletrial : make an alarm lok ring J 10 Manufaturers ould hange the way the devie was tested or misrepresent the test results to make it appear more energy effiient that it really is. 11 a The SudZ mahine is more energy effiient. The SudZ mahine requires fewer joules. Although the differene in energy use etween the two washing mahines may e small for one wash, the differene in energy use etween the two mahines will e large over the total life of the washing mahines. 12 a Chemial energy heat energy The solution would not remain at 29 C all day. The heat energy produed will e gradually transferred to the eaker and the air. This happens eause heat energy flows from the higher temperature solution to the lower temperature glass and air. The energy flow will ontinue until the solution has the same the temperature as that of the surroundings. 13 Individual student response required. Thinking sientifially 1 B 2 B 3 C 4 C Copyright Pearson Australia 2011 (a division of Pearson Australia Group Pty Ltd) ISBN Page 8