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Slide number 1 Subject Knowledge – Energy – Download K4.5_1.0a
Subject Knowledge - Energy
This document can be freely copied and amended if used for educational purposes. It must not be used for commercial gain. The author(s) and web source must be acknowledged whether used as it stands or whether adapted in any way.
Subject Knowledge – Energy (Download K4.5_1.0a)
Authored by Keith Ross, University of Gloucestershire
accessed from http://www.ase.org.uk/sci-tutors/
date created Nov 2005
Slide number 2 Subject Knowledge – Energy – Download K4.5_1.0a
Energy – the big ideas
1. Can we use energy up? – yes??
2. Do Fuels contain energy - no!!
3. Is Heat the same as temperature - no!!
4. Does turning the ignition key provide energy to make the car go – no!
5. Replenishable energy and the environment.
Slide number 3 Subject Knowledge – Energy – Download K4.5_1.0a
Two major misconceptions
The two major misconceptions about energy arise because of these two confusions. We need to ensure out students distinguish between:
1. Energy itself (joules) and usefulness of energy. 2. Fuel (made of matter) and energy (measured in
joules).
At this stage (key stages 1-4) don’t worry about e=mc2 (mass energy equivalence)
Slide number 4 Subject Knowledge – Energy – Download K4.5_1.0a
1. Useful energy?1. Useful energy?
“I was always confused by the word energy. I always knew it was useful but could never explain precisely to anyone what it is.
“I now realise that energy can be described in two ways ... that its usefulness can be used up ... yet the amount of energy remains the same.” Extracts from a learning log written
by a BEd Primary student where they attempt to identify changes in their understanding as a result of their study.
Slide number 5 Subject Knowledge – Energy – Download K4.5_1.0a
‘Using energy’
• High grade energy resources are used up
• .. but joules in = joules out
Slide number 6 Subject Knowledge – Energy – Download K4.5_1.0aReturn to main menu
Slide number 7 Subject Knowledge – Energy – Download K4.5_1.0a
2. Do Fuels contain energy - no!!
The following questions were put, electronically, to a group of 120 year one trainee primary teachers who all achieved a grade ‘c’ or better at GCSE science two or more years ago. Figures show % who chose each option.
Red figures suggest misconceptions
Green figures suggest useful understanding
The questions were re-administered at the end of year one, and the slides show changes in choices following a year’s science subject study
Some slides are extracts from learning logs written by the same group of students where they attempt to identify changes in their understanding as a result of their study.
Slide number 8 Subject Knowledge – Energy – Download K4.5_1.0a
Many people say that fuels and food ‘contain’ energy.
Many people say that fuels and food ‘contain’ energy.
How do you imagine energy to be associated with, or 'in', fuels and food?
(a) When fuels burn or food is respired the energy in them is released.
(b) Fuels and food contain energy-rich bonds which release energy when the bonds break.
(c) Energy can only be obtained by making new bonds. This happens during burning and respiration.
(d) The energy is not in the fuel or food itself, but is associated with both the fuel and oxygen.
Slide number 9 Subject Knowledge – Energy – Download K4.5_1.0a
Many people say that fuels and food ‘contain’ energy.
Many people say that fuels and food ‘contain’ energy.
How do you imagine energy to be associated with, or 'in', fuels and food?
(a) When fuels burn or food is respired the energy in them is released.
(chosen by 80% before study - 17% after)
(b) Fuels and food contain energy-rich bonds which release energy when the bonds break. (85% to 35%)
(c) Energy can only be obtained by making new bonds. This happens during burning and respiration. (17% to 65%)
(d) The energy is not in the fuel or food itself, but is associated with both the fuel and oxygen. (50% to 95%)
Slide number 10 Subject Knowledge – Energy – Download K4.5_1.0a
Conservation of MatterConservation of Matter
When something is dumped on the rubbish tip, goes up the chimney or down the drain, its atoms:
(a) may eventually cease to exist (chosen by half before study - 5% after) (b) may remain harmlessly in the environment
(c) may be used by living things to help them grow
(d) may remain in the environment and cause pollution
Slide number 11 Subject Knowledge – Energy – Download K4.5_1.0a
Fate of food we eatFate of food we eatConsider the material (stuff, matter, atoms...)
in our food that enters our blood and which we have used as a fuel. How does this material leave our body?
(a) The atoms are all used up and only energy is left. Chosen by 37% at start and by 2% at end(c) We breathe a lot of it out as carbon dioxide and
water vapour.(38% to 77%)
Slide number 12 Subject Knowledge – Energy – Download K4.5_1.0a
Primary ITT student with C at GCSE - learning log extracts
Primary ITT student with C at GCSE - learning log extracts
“I found the principles of burning very enlightening. The constructive process of oxygen forming oxides resulting in an increase in weight now seems very obvious.”
Slide number 13 Subject Knowledge – Energy – Download K4.5_1.0a
Primary ITT student with C at GCSE - learning log extracts
Primary ITT student with C at GCSE - learning log extracts
“I gradually came to realise how much of a part ‘atoms’ do play in matter.
“I have always assumed that as materials go though the process of change, the atoms from which they are made up, change too.
“However, this unit helped me to understand that atoms are indestructible and I can look at any substance now and judge that ..
“.. regardless of what change it goes through the atoms will remain the same.”
Slide number 14 Subject Knowledge – Energy – Download K4.5_1.0a
DemonstrationsDemonstrations
• Char and flame
• Syrup tin
• Candle and methane
• Match and methane
Slide number 15 Subject Knowledge – Energy – Download K4.5_1.0a
The stretched oxide modelThe stretched oxide model
• The model shows oxygen being ‘dragged away’ from carbon dioxide and water to form free oxygen and leave behind carbohydrate.
• This is the process that happens in photosynthesis, driven by solar energy
In the following slides:Oxygen or processes involving oxygen are coloured red.Fuels, food, etc not oxidised are green
Slide number 16 Subject Knowledge – Energy – Download K4.5_1.0a
An Ecosystem?An Ecosystem?
PhotosynthesisRespiration
Oxygen used
Fuel line
Oxygen produced
Solar cell
Electrolysis of water
Fuel cell
Electric motor
Slide number 17 Subject Knowledge – Energy – Download K4.5_1.0a
The two meanings of ‘burn’The two meanings of ‘burn’
• The next few slides show a vital distinction between digestion and respiration – processes that get confused in the minds of children.
• The same distinction needs to be made between the two meanings of ‘burn’: char and combust
Slide number 18 Subject Knowledge – Energy – Download K4.5_1.0a
Adding energy to Food and fuelAdding energy to Food and fuel
• Heating decomposes it into (char)coal, oil and inflammable smoke (gas)
• Digestion decomposes it to faeces, blood sugar and inflammable gas (flatulence)
• These are all still fuels and can flame-burn – these are endothermic processes, requiring an input of energy
Slide number 19 Subject Knowledge – Energy – Download K4.5_1.0a
Getting energy from Food and fuelGetting energy from Food and fuel
• Combustion and Respiration add oxygen to form carbon dioxide and water
• These are oxides. The processes are exothermic, transferring useful energy.
• The oxides can be ‘re-charged’ by solar energy during photosynthesis to reform fuel/food and oxygen
Slide number 20 Subject Knowledge – Energy – Download K4.5_1.0a
The rich Gambian LanguagesThe rich Gambian Languages
burn English
flame-burn char-burn English
maala jani Mandinka
taka laka Wolof
Slide number 21 Subject Knowledge – Energy – Download K4.5_1.0a
Emphasise the distinction between matter and energyEmphasise the distinction
between matter and energy• Life-world view - biomass (eg. cornflakes, wood )
is energy. • Call it fuel which combines with oxygen (matter) • The energy associated with them is like a spring -
• stretched (energy stored as fuel and oxygen kept apart)
• when relaxed (energy released as oxides re-form).
In the following slides:The everyday life-world view is coloured blueSuggestions for teaching approaches follow
Slide number 22 Subject Knowledge – Energy – Download K4.5_1.0a
Emphasise that gases are the material products of combustion
Emphasise that gases are the material products of combustion
• Life-world view - flames, hot air, exhaust gases are forms of energy – “they are weightless”.
• Account for matter during evaporation and burning.
• Collect exhaust gases from above a flame and see the water condense
Slide number 23 Subject Knowledge – Energy – Download K4.5_1.0a
Use the atom concept primarily to explain the conservation of matterUse the atom concept primarily to explain the conservation of matter
• Life-world view - atoms come and go like bulk materials which burn, evaporate react.
• Distinguish between indestructible atoms and bulk materials– water evaporates but the atoms are still there
• Introduce chemical equations with ball and stick models or drawings to allow the actual atoms can be counted on each side.
Slide number 24 Subject Knowledge – Energy – Download K4.5_1.0a
Count the atomsCount the atoms
carbohydrate + oxygen = water + carbon dioxide
O
O
O
O
CO
H
HOC
H
H
CHOH + O2 = H2O + CO2
carbohydrate + oxygen = water + carbon dioxide
CHOH + O2 = H2O + CO2
Slide number 25 Subject Knowledge – Energy – Download K4.5_1.0a
Emphasise digestion as the process by which food enters the
blood.
Emphasise digestion as the process by which food enters the
blood.• Life-world view - food goes from mouth to
anus along the alimentary canal
• Food's path is mouth – digestive system – blood – cells. Then:• 90% is a fuel - joins with oxygen, and leaves the body
at the lungs (and as water in urine).
• 10% is for growth - adds to body biomass by helping to construct new cells.
Slide number 26 Subject Knowledge – Energy – Download K4.5_1.0a
Emphasise digestion as the process by which food enters the blood.
Emphasise digestion as the process by which food enters the blood.
• “Where does the food which you eat leave the body”
• Life-world view “it leaves as faeces”. • … but faeces are still fuel (food), and have never
really entered the body and have not yet joined with oxygen.
• Encourage them to say “it leaves from the lungs and in urine” or (for the 10% of our food used to replace body tissue) “as house dust”
Slide number 27 Subject Knowledge – Energy – Download K4.5_1.0a
Emphasise the constructive side to burning (combustion) and respirationEmphasise the constructive side to
burning (combustion) and respiration
• Life-world view burning is a destructive process - only ashes remain.
• Encourage pupils to see exhaust gases as massive, an increase in mass as oxides are built up
• See Water and carbon dioxide we breathe out as oxidation products of the food we eat
• See the ashes left after a wood fire, as oxides of the metals that were taken in as minerals during the lifetime of the tree.
Slide number 28 Subject Knowledge – Energy – Download K4.5_1.0a
Emphasise the role of oxygen in burning (combustion) and respiration
Emphasise the role of oxygen in burning (combustion) and respiration
• Life-world view air keeps us alive.
• Emphasise: panting; starving the brain of oxygen; smothering a fire etc. all as evidence for the constructive role of oxygen.
Slide number 29 Subject Knowledge – Energy – Download K4.5_1.0a
Avoid the use of the term ‘high energy bond’ in ATP (at A level)Avoid the use of the term ‘high
energy bond’ in ATP (at A level)• The third phosphate group in ATP is weakly bonded to the
rest of the molecule. • It costs much less than the usual 400 kj per mole to break. • ATP is therefore a reactive molecule. • By breaking this weak bond and replacing it with a
stronger bond, energy is made available to do useful things in the cell.
• Energy from the glucose-oxygen system is used to to re-set the system – this energy:• breaks the strongly bonded -OH group from ADP and replaces it
with the weakly bonded third phosphate of ATP again.
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Slide number 30 Subject Knowledge – Energy – Download K4.5_1.0a
2 other confusions
3. Heat and temperature
4. Control systems
Slide number 31 Subject Knowledge – Energy – Download K4.5_1.0a
Heat and temperatureYou add 10 kettle-fulls of boiling water to
some cold water in a bath to make the bath water warm.
true or false: the bath water now has more heat energy in it than a kettle full of boiling water.
38% said the bath had less heat in it than the kettle
Slide number 32 Subject Knowledge – Energy – Download K4.5_1.0a
Temperature
ii. when the water from the two cups are mixed
Figure 4.2 (From Stavy and Berkovitz 1980)
i. when water at 600C in a jar is shared between two cups
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Slide number 33 Subject Knowledge – Energy – Download K4.5_1.0a
5. Energy and the environment
Renewable or replenishable energy?
Since energy becomes degraded (as matter is cycled) we cannot actually renew energy, though the matter in which the energy is stored can be renewed, or re-charged.
Thus it is better to call energy sources that can be re-charged: replenishable
Slide number 34 Subject Knowledge – Energy – Download K4.5_1.0a
• Use of man power to move a statue in Egypt, about 2000 B.C. Today we each have the services of more energy slaves than are pulling the statue in this picture.
• (Wilson A.W. (1976) “What is Energy” Exeter: Wheaton)
Slide number 35 Subject Knowledge – Energy – Download K4.5_1.0a
Human muscles• A well-nourished slave produced about 3 Mj* of
energy a day through respiration• We each ‘use’ an average of about 400 Mj a day
in our industrial society• To produce 400 Mj a day we would therefore each
need 160 slaves – pedalling away at cycle generators.
• To grow food for this muscle power (even if they were draught animals) would need the land areas of several Earths (our global footprint)
*million joules
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http://www.footprintnetwork.org/