Subject Knowledge - Energy
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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 1
Subject Knowledge – Energy – Download K4.5_1.0a
Energy – the big ideas
Can we use energy up? – yes??
Do Fuels contain energy - no!!
Is Heat the same as temperature - no!!
Does turning the ignition key provide
energy to make the car go – no!
5. Replenishable energy and the
environment.
1.
2.
3.
4.
Slide number 2
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 3
Subject Knowledge – Energy – Download K4.5_1.0a
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
Slide number 4
by a BEd Primary student where they
attempt to identify changes in their
understanding as a result of their
study.
Subject Knowledge – Energy
– Download K4.5_1.0a
‘Using energy’
• High grade energy resources are used up
• .. but joules in = joules out
Slide number 5
Subject Knowledge – Energy – Download K4.5_1.0a
Slide number 6
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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 7
Subject Knowledge – Energy – Download K4.5_1.0a
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 8
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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 9
Subject Knowledge – Energy – Download K4.5_1.0a
Conservation 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 10
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Fate of food we eat
Consider 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 11
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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 12
Subject Knowledge – Energy – Download K4.5_1.0a
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 13
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Demonstrations
•
•
•
•
Char and flame
Syrup tin
Candle and methane
Match and methane
Slide number 14
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In the following slides:
Oxygen or processes involving oxygen are
coloured red.
Fuels, food, etc not oxidised are green
The 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
Slide number 15
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An Ecosystem?
Oxygen
used
Fuel line
Fuel cell
Electrolysis of
water
Oxygen
produced
Electric
motor
Solar cell
Photosynthesis
Slide number 16
Respiration
Subject Knowledge – Energy – Download K4.5_1.0a
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 17
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Adding 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 18
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Getting 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 19
Subject Knowledge – Energy – Download K4.5_1.0a
The rich Gambian Languages
burn
flame-burn
maala
taka
Slide number 20
char-burn
jani
laka
English
English
Mandinka
Wolof
Subject Knowledge – Energy – Download K4.5_1.0a
In the following slides:
The everyday life-world view is coloured blue
Suggestions for teaching approaches follow
Emphasise 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).
Slide number 21
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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 22
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Use 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 23
Subject Knowledge – Energy – Download K4.5_1.0a
Count the atoms
carbohydrate + oxygen = water + carbon dioxide
CHOH
+ O2
H
H
C
= H2O
O
O
O
+
CO2
O
H
O
C
H
O
Slide number 24
Subject Knowledge – Energy – Download K4.5_1.0a
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 25
Subject Knowledge – Energy – Download K4.5_1.0a
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 26
Subject Knowledge – Energy – Download K4.5_1.0a
Emphasise 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 27
Subject Knowledge – Energy – Download K4.5_1.0a
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 28
Subject Knowledge – Energy – Download K4.5_1.0a
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 reset the system – this energy:
• breaks the strongly bonded -OH group from ADP and replaces it
with the weakly bonded third phosphate of ATP again.
Slide number 29
Subject Knowledge – Energy – Download K4.5_1.0a
Return to main menu
2 other confusions
3. Heat and temperature
4. Control systems
Slide number 30
Subject Knowledge – Energy – Download K4.5_1.0a
Heat and temperature
You 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 31
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Temperature
i.
ii.
when water at 600C in a jar is shared between two cups
when the water from the two cups are mixed
Figure 4.2 (From Stavy and Berkovitz 1980)
Slide number 32
Subject Knowledge – Energy – Download K4.5_1.0a
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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 33
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 34
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)
http://www.footprintnetwork.org/
*million joules
Slide number 35
Subject Knowledge – Energy – Download K4.5_1.0a
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