# TSST-energy.ppt

28 de May de 2023
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### TSST-energy.ppt

• 2. Why & how teach energy? In small groups, discuss:  Why and how is energy taught at KS3?  What do students gain from it?  Is this a useful preparation for GCSE & A-level studies? Jot a few things down so that you can report back. 5 minutes 2
• 3. It’s easy to go wrong In what way is each of these statements wrong? 1. ‘The moving pencil uses kinetic energy.’ (QCA) 1. ‘The steam [from a volcano vent] is converted into energy and transported to Europe via a 1,200-mile sea-floor cable.’ (a London newspaper) 1. ‘Carbonaceous matter is converted to heat or other forms of energy.’ (Physics World) 2. ‘Energy makes things happen.’ (ASE Big Ideas) 1. ‘The bulb lights because energy flows from the battery to the bulb.’ (Sophie, Year 9) 3
• 4. Energy historically Steam engines: • 1712 Newcomen, efficiency ~1%, • 1775 Boulton & Watt, efficiency ~7%
• 5. Energy and power by analogy time power energy   measured in joules, MJ or kWh time flow me water volu   measured in litres time energy power  measured in joules per second, W, MW, GW, TW, kWh per day water time volume flow  measured in litres per minute
• 6. Energy today How many Mars bars would I need to climb a mountain? How much coal/oil do I use in a day? Will UK electricity production match peak demand? Can the Sun supply the world’s energy needs? What is the efficiency of a motor? How high can a projectile go? Answering questions like this requires a calculation. 6
• 7. Learning outcomes • describe physical processes in terms of energy stores and transfers • distinguish between temperature and internal energy • explain thermal transfers (conduction, convection, radiation) • calculate the specific thermal capacity of metal objects • discuss energy changes associated with change of state (latent heat) • explain the law of conservation of energy, calculate efficiency in energy transfers and recognise dissipation • relate work done by a force to and • describe rate of mechanical working as power • apply energy concepts to decision-making about energy policy • use a variety of experiments to convey key ideas about energy Ep = mgh Ek = mv2 2
• 8. Teaching challenges • ‘Energy’, an everyday word, in science is an abstract quantity. • Energy conservation defies common sense, as everyday things ‘run out of energy’. • Simply naming different types of energy, or energy chains, provides no explanation for physical processes. • Students find work done (force exerted over a distance) more difficult than impulse (force exerted over an interval of time). • Although temperature is a very familiar and tangible property, it needs to be associated with the random thermal motion of particles inside a body (internal energy).
• 9. What is ‘energy’? ‘A certain quantity that does not change’ ‘It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.’ Richard Feynman The law of conservation of energy
• 10. Energy stores & pathways Practical Physics guidance notes • Helpful language for energy talk • What’s wrong with ‘forms of energy’? • Does energy make things happen?
• 12. A circus of energy experiments Working in pairs, do as many experiments as you can. ~30 minutes [please do NOT write on instruction sheets]
• 13. Mechanical energy For an object starting from rest, Work done Therefore no surprise that, in some mechanical systems, e.g. roller coaster, or pendulum W = F ´displacement = F ´(average velocity´time) W = Ft ´ v 2 = mv( v 2 ) = mv2 2 impulse = force´time = mv mgh+ mv2 2 = constant
• 14. ‘Mechanical equivalent of heat’ Early in 19th C, ‘heat’ was thought to be a fluid, called ‘caloric’. Many experiments, mainly 1840 – 1900, showed conversions of heat to/from mechanical or electrical sources, leading to the concepts of energy & energy conservation. James Prescott Joule, Manchester brewer & amateur scientist. 40 expts! e.g. Swiss honeymoon: thermometer to measure temperature of water at top & bottom of a waterfall. 1850 article, Philosophical Transactions (Royal Society) Clausius, Thomson (Lord Kelvin), Helmholtz, Rankine T c t m h g t m    C kg J c o 4200 water, of capacity heat specific 
• 15. Students often confuse … Thermal energy (store) Temperature Heating (pathway) Average energy per particle e.g. a sparkler is hot (high temperature) because each particle of metal has lots of energy e.g. a bath full of water is not as hot (lower temperature) because each particle has less energy. Directly measurable. Total energy of the system Depends on number of particles in a body and the energy of each one e.g. a sparkler has less energy than a bath full of water because there are many more particles in a bath. A process or pathway which changes the energy store of an object 15
• 17. Thermal transfers Energy transfer from one store to another because of a temperature difference. conduction: Ek transferred from atom to atom convection: bulk movement of a fluid caused by localised thermal expansion and hence differences of density in the fluid. radiation: warm body emits a continuous spectrum of electromagnetic radiation, with peak frequency related to absolute temperature.
• 18. Heat capacity thermal store associated with a temperature change but no change of state. Start simple: Why is a bite of hot potato more likely to burn the tongue than a bite of cabbage at the same temperature? Which foods stay hot longer on your plate? Thermal (heat) capacity of an object: energy stored or released by an object per degree of temperature change, in J oC-1 ‘Specific’ thermal capacity: energy stored or released by a kg of material per degree of temperature change, in J kg-1 oC-1 Materials used as coolants have a high specific thermal capacity. Table T mc Q  
• 19. Experiments to determine c • Electrical method • Method of mixtures e.g. solid placed in water energy lost by hotter object = energy gained by cooler object NOTE: Both the equations above assume no heat loss. Insulate calorimeter & include it in calculations. • Using a cooling curve ref: Nelkon & Parker Advanced level Physics Practical Physics Energy collection ‘Thermal physics’ T mc IVt    object by gained energy supplied energy electrical temp m equilibriu the is where , ) ( ) ( 3 2 3 2 2 1 3 1 1 T T T c m T T c m   
• 20. Latent heat thermal store associated with a change of state but no temperature change. Term ‘latent’ introduced ~1750 by Joseph Black [derived from the Latin latere, to lie hidden]. Fusion: reversible change solid to liquid Vaporisation: reversible change liquid to vapour Table heat latent specific mass  Q
• 21. Cooling or heating curves previously schools used naphthalene (now hexadecanol)
• 23. Latent heat Experiments • Fusion: Melting ice in a calorimeter • Vapourisation: passing steam through a calorimeter; electrical method. References: Nelkon & Parker Advanced level Physics, Practical Physics Energy collection ‘Thermal physics’ Applications releasing energy as liquid changes to solid • hot pad hand-warmer • thermal energy storage in buildings
• 24. UK Energy futures David MacKay, Sustainable energy – without the hot air Concerns about UK energy policy: • Fossil fuels are a finite resource • Security of energy supply – for the UK population and the economy – not reliant on foreign energy sources – diversified sources mean more robust • CO2 and climate change ‘Numbers, not adjectives’
• 25. A balance sheet Energy consumed Energy produced Cars Wind Planes Solar Heating and cooling Hydroelectricity Lighting Offshore wind Gadgets Waves Food and farming Tide Stuff – materials from cradle to grave Geothermal Public services Fossil fuels - coal, oil and gas Energy industries Nuclear
• 26. Ben Goldacre, Bad science 12 December 2009 Climate change? Well, we’ll be dead by then ‘Zombie arguments survive, immortal and resistant to all refutation, because they do not live or die by the normal standards of mortal argument.’
• 27. In the science classroom? Carefully structured discussions to develop skill in policy-related argument, based on • science, if possible including quantitative estimates • social values • a basic understanding of how collective (social, political and economic) decisions are made in the UK … simplifying the breadth and depth of science to match pupils’ age and ability
• 28. Useful websites Climateprediction.net follow links Support -> Schools Realclimate.org climate scientists’ blog and archive Google Earth v5 time series images show impact of climate change UK Energy Flows comprehensive Sankey diagram published every 3 years The Guardian pages on Climate change - plus related Environment pages … and weblinks
• 29. Support, references www.talkphysics.org SEP Energy now! cdrom, 3 booklets Energy storage, Solar power, Wind power Energy topic, Practical Physics website, including Guidance pages David Sang (ed, 2011) Teaching secondary physics ASE / Hodder