Gill
Science
Stage 4
S
Part 3 – Using the energy
concept
S 43923
Number: 43923
Energy
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Extracts from Science Syllabus Years 7-10 © Board of Studies, NSW 2003
Overview pp 3-5
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Contents – Part 3
Lesson 11: Life and energy
3
Chemical changes and life
3
Energy and food chains
6
Lesson 12: Energy transfers and transformations
11
Energy efficiency
13
Electrical energy
15
Lesson 13: Resources
17
Natural resources
17
Made resources
18
Fossil fuels
19
Non-renewable sources of energy
19
Renewable sources of energy
20
Lesson 14: Energy technology
23
Energy transformations to electrical energy
24
Energy technology using steam
24
Lesson 15: Using models, theories and laws
29
How science works
29
The particle model of matter
30
A model could become a theory
31
Theories and laws
33
Suggested answers – Part 3
35
Exercises – Part 3
41
Part 3: Using the energy concept
1
2
Energy
Lesson 11: Life and energy
Most life on Earth depends on energy from the Sun. If no sunlight reached
Earth there would be no plants or animals. All that would be left alive would
be the sort of bacteria that obtain energy from chemicals. And most of these
would die as the Earth cooled from the loss of sunlight energy.
Chemical changes and life
A chemical change occurs when a new substance is produced. Chemical
changes are also called chemical reactions or reactions for short.
The two most important chemical reactions for living things are:
•
photosynthesis which traps light energy from the Sun
•
respiration which provides energy to keep living things alive and
their bodies working.
Photosynthesis
Photosynthesis is carried out in the green parts of plants. Photosynthesis
changes light energy to chemical energy stored in a sugar called glucose.
Photo means light while synthesis means to make or put together. In
photosynthesis light energy is used to put together small particles of carbon
dioxide (CO2) and water (H2O) to form larger particles of glucose
(C6H12O6).
Activity: Chemical formula – what does it stand for?
A chemical formula is a shorthand way of showing what atoms are in a pure
chemical.
C represents a carbon atom, H represents a hydrogen atom and O represents
an oxygen atom.
The formula CO2 shows that a particle of carbon dioxide is made up of one
C and two O, that is, one carbon atom and two oxygen atoms.
Part 3: Using the energy concept
3
Fill in the missing parts of the table below:
Chemical
Formula
Carbon
atoms
Hydrogen
atoms
Oxygen
atoms
carbon dioxide
CO2
1
-
2
water
H2O
glucose
C6H12O6
Compare your answers with the suggested answers. If any of your answers
are different check the numbers in the formula.
Oxygen (O2) is also produced by photosynthesis. The chemical reaction for
photosynthesis can be written as a word equation.
carbon dioxide + water → glucose + oxygen
The
means produces so the equation can be read as: carbon dioxide plus
water produces glucose plus oxygen.
The light energy trapped by the green chlorophyll in plants is used to make
this reaction occur. The chemicals on the right hand side of
in this
reaction contain more energy than the chemicals on the left hand side of .
The light energy has been transformed to chemical energy in glucose.
Respiration
Respiration is an energy releasing reaction that occurs in all parts of all
living things. The energy released is what keeps a living thing alive.
In humans the glucose and oxygen needed for respiration is carried to all
parts of the body by blood. The carbon dioxide and water produced by
respiration are carried away from different parts of the body in the blood.
In respiration chemical energy in the glucose is transformed to the heat
energy, kinetic energy, electrical energy and other forms of energy that
appear in the bodies of living things.
The chemical reaction for respiration can be written as a word equation:
glucose + oxygen → carbon dioxide + water
Or, the reaction can be read as ‘glucose plus oxygen produces carbon
dioxide plus water’.
Did you notice ways in which the equations for photosynthesis and
respiration are similar or different?
4
Energy
Comparing photosynthesis and respiration
Compare means show how things are different or similar.
Photosynthesis: carbon dioxide + water → glucose + oxygen
Respiration: glucose + oxygen → carbon dioxide + water
The chemicals that react, shown on the left hand side of the arrow, are called
reactants. The chemicals that are produced, shown on the right hand side of
the arrow, are called products.
Use the terms reactants and products to complete these sentences about how
photosynthesis and respiration are similar:
The ___________in photosynthesis are the same as the ______________ in
respiration while the ______________ in photosynthesis are the same as
the________________ in respiration.
The reactants in photosynthesis are the same as the products in respiration
while the products in photosynthesis are the same as the reactants in
respiration.
Or, you could have written: The products in photosynthesis are the same as
the reactants in respiration while the reactants in photosynthesis are the
same as the products in respiration.
If ENERGY is added to the two equations you will notice a way in which
photosynthesis and respiration are different.
Photosynthesis: ENERGY carbon dioxide + water → glucose + oxygen
Respiration: glucose + oxygen → carbon dioxide + water + ENERGY
Photosynthesis is an energy absorbing reaction requiring energy input.
Respiration is an energy releasing reaction providing energy output.
SPIRATION
RE
ENERGY INPUT
YN
TOS THES
HO
IS
glucose
+
oxygen
ENERGY OUTPUT
P
carbon dioxide
+
water
Energy in respiration and photosynthesis
Part 3: Using the energy concept
5
The role of photosynthesis is to store light energy as chemical energy. The
role of respiration is to provide energy for life from this chemical energy
Energy and food chains
A food chain shows a feeding relationship; what eats what.
A food chain can be shown using a diagram:
Or, a food chain can be shown just using words: grass → bird → cat
The
can mean ’is eaten by’ or can show the flow of energy through the
food chain. Note that an arrow in a food chain has a different meaning
compared with an arrow in a chemical equation.
A food chain always starts with a plant able to change light energy into
chemical energy. Plants are called producers because they produce their
own food. All the other living things in the food chain are called consumers
as they cannot produce their own food.
When the plant is eaten, chemicals in the plant provide energy to the planteating animal. When a bird is eaten by a cat, the chemicals in the bird
provide energy to keep the cat alive.
The chemical energy stored in glucose can be used by:
•
plants
•
animals which eat plants
•
animals that eat animals which eat plants
•
animals that eat both plants and animals.
Activity: Carnivores, herbivores and omnivores
Have you seen the terms carnivore, herbivore and omnivore before? Try to
match these three words with the definitions and examples below:
Term
6
Definition
Example
plant eater
bird
animal eater
cat
plant and animal eater
human
Energy
Check that you had the bird as a herbivore, cat as a carnivore and human as
an omnivore.
The energy that a bird, a cat and a human use to keep alive came from
chemical energy in glucose. This chemical energy came from light energy
that was trapped in photosynthesis.
An Australian food chain example
rose sap → scale insect → ladybird → wagtail → hawk
Scale insects are very small animals. They eat the sap of some plants,
especially roses. Ladybird beetles eat scale insects. Willy wagtail birds love
to eat ladybird beetles, and hawks eat wagtails.
Do you think the food chain means that one hawk eats one wagtail only? Or
maybe one ladybird eats one scale insect only? No, they need more food
than that.
Several wagtails would make a good meal for a hawk. It would take a large
number of ladybirds to feed a wagtail and a still larger number of scale
insects to feed a ladybird.
The numbers below are estimates of how many of each kind of living thing
are needed to supply the food in the chain.
rose sap
lots
→
scale insect
1000s
→
ladybird
100s
→ wagtail →
3
hawk
1
So one hawk might eat three wagtails a day. But three wagtails might each
need to eat 100 ladybirds for their energy. And 100 ladybirds might each
need to eat 1000 scale insects. These insects need to be feeding on lots of
rose sap.
At each step in a food chain, energy is lost, mostly as heat.
What is a food pyramid?
Another way to look at the relationship between organisms in a food chain
is to draw a food pyramid. The diagram following is a food pyramid.
Part 3: Using the energy concept
7
A food pyramid
Notice that the sections get smaller towards the top of the pyramid.
The producer is always at the base of the pyramid. The top consumer is
always at the apex (top point) of the pyramid.
Approximately 10% of energy is transferred from one living thing to its
consumer. It follows then that the mass of plants eaten is much greater than
the mass of animals that feed on them and so on. This gives the pyramid
shape.
Notice that:
•
the food pyramid contains all the organisms in the food chain
•
the producer is on the bottom of the pyramid
•
the relative number of organisms usually gets smaller up the pyramid
•
each section gets smaller up the pyramid
•
the energy needed to support organisms in the food chain is more at
the base of the pyramid and less at the top.
Ecosystems and food webs
An ecosystem is a space where living things are interacting. Some examples
of ecosystems are a rainforest, a coral reef, a lake or a grassland.
In an ecosystem there are many food chains. If food chains are linked
together the linked food chains are called a food web. A diagram of
connected food chains does look a bit like a spider’s web.
8
Energy
Activity: Understanding a food web
Look carefully at the food web in an Australian grassland ecosystem:
eagle
fox
rabbit
bandicoot
pasture grass
wild grass
tree roots
Food web of an Australian grassland ecosystem
a) List the consumers.
_________________________________________________________
b) Identify the organisms eaten by the fox?
_________________________________________________________
c) Name the producers.
_________________________________________________________
d) Which of the following organisms could best take the place of the rabbit
in this food web? Is it a dog, a cat, a pigeon or a wallaby? Give a reason
for your answer.
_________________________________________________________
_________________________________________________________
e) Why would there be more rabbits than eagles in this community? Use
energy in your answer.
_________________________________________________________
Part 3: Using the energy concept
9
f)
Draw a food pyramid to show the relative numbers and energy flow in
the feeding relationship between pasture grass, rabbits and foxes in this
community.
Compare your answers.
Complete the Exercise 3.1: How well do you understand food pyramids?
10
Energy
Lesson 12: Energy transfers and
transformations
This lesson distinguishes between energy transfer and energy transformation
then shows you how to use energy information available at home.
Activity: Investigating energy transfer and energy transformation
What you need
•
two rulers
•
marbles or round lollies such as Jaffas, Koolmints or Jilamints
What you do
1
Find a horizontal surface such as a flat tabletop or desktop. Arrange the
two rulers side by side with edges between half and one centimetre
apart.
2
Check that a marble/round lolly can fit in the groove between the two
rulers. If not adjust the gap between the ruler edges.
3
Check that the marble/round lolly rolls freely along the groove if it is
flicked with a finger. If it doesn’t then adjust the equipment:
4
5
• are the ruler edges smooth enough?
• does the groove width need adjustment?
• are the marbles/round lollies you are using round enough?
Place five marbles/round lollies together in the groove so that they are
touching one another.
Flick another marble/round lolly from the end of the groove so that it
rolls along the groove and hits the row of lollies.
What you observed
1
Describe what happened when the marble/round lolly hit the row. What
did you see? What did you hear?
_________________________________________________________
_________________________________________________________
Part 3: Using the energy concept
11
2
Which of your observations was an energy transfer, that is, the transfer
of the same form of energy from one location to another?
_________________________________________________________
_________________________________________________________
3
Which of your observations was an energy transformation in which
some of the kinetic energy of the marble/round lolly was transformed to
another type of energy?
_________________________________________________________
_________________________________________________________
Conclusion
Explain the difference between an energy transfer and an energy
transformation using examples from this activity.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
Compare your response for this activity with those in the suggested answers
section.
Demonstrate hygienic work practices by placing any round lollies used in
the waste bin. Do not allow anyone to eat them!
Activity: Classifying energy transfers and energy transformations at
home
Many energy transfers and energy transformations at home involve electrical
appliances.
Remember that:
•
in a transfer it is the same form of energy that is transferred from one
location to another location
•
in a transformation one form of energy is transformed to at least one
other form of energy.
In the table below one transfer and one transformation have been done for
you. If you decide on a transfer show the type of energy. If it is a
transformation show the energy change.
12
Energy
Change
Transfer/transformation
Energy
operate an electric fan
transformation
electrical → kinetic
moving fan blade moves air
transfer from blades to air
kinetic
toaster heats bread
gas burns in heater
turn on electric light
use microwave oven
turn on radio
use hot water bottle
use battery
Check your answers.
Energy efficiency
When energy is transferred or transformed some of the energy is lost.
The energy doesn’t disappear. Some of it just doesn’t make it to where it
was supposed to go in a transfer. For example, in cooking bread in a toaster,
some of the heat rays transfer energy to other parts of the toaster instead of
the bread. In a transformation some of the energy changes to forms that are
not wanted. For example the electric motor in a fan changes some of the
electrical energy to heat instead of kinetic energy of air.
If the amount of energy input and the amount of energy output are known
the efficiency can be calculated:
efficiency =
output
input
Why can’t the output of energy be greater than the input of energy?
The Law of conservation of energy states that energy cannot be created.
You cannot get more energy out than what you put in. Some of the energy
you put in will be changed to unwanted forms of energy or transferred to
locations that you don’t want it to go to. So the ouput is always less than the
input.
Efficiency is often stated as a percentage.
% efficiency =
Part 3: Using the energy concept
output 100
×
input
1
13
Activity: Calculating and comparing the energy efficiency of microwave
ovens
On the back or side of a microwave oven you can find a label giving input
and output information.
Among this information you should find watts (W) of input and watts (W)
of output. A watt is a joule per second. So comparing watts is the same as
comparing joules of energy per second.
Dividing the output watts by the input watts will give you the efficiency.
Using the percentage key on a calculator will give you efficiency as a
percentage.
Look at these information labels from two microwave ovens:
NEC domestic microwave oven, model 726
14
Energy
NEC domestic microwave oven, model 668
Calculate the efficiency of each oven to decide which is the most efficient.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
Check your calculations.
Electrical energy
Try to imagine your life without any electrical energy, and that includes
electrical energy from batteries!
No phones, no TV, no radio, no computers, no recorded music, no
microwaved food, no lighting or airconditioning of homes or buildings, no
cars, buses or trains. No communication systems! Chaos on city roads
without traffic lights! Even gas heating at home probably has an ignition and
control system that requires electrical energy to work!
You’ve probably noticed that you have at least two wires supplying
electrical energy to your home, a plug connected to the electricity supply
has at least two pins and that a battery has two terminals.
Part 3: Using the energy concept
15
A simple model of electrical energy has electrically charged particles
flowing in one wire/plug/terminal and out the other wire/plug/terminal.
Between the wires/plugs/terminals are electrical circuits through which the
electricity can flow. Each electrical circuit is a pathway for the transfer of
electrical energy.
When a switch is turned on the charged particles can move through an
appliance and their electrical energy transformed to another form of energy.
Lighting circuit: electrical energy → light energy
Heating circuit: electrical energy → heat energy
Motor circuit: electrical energy → kinetic energy
Complete the Exercise 3.2: Energy ratings of electrical appliances.
16
Energy
Lesson 13: Resources
Natural resources
Natural resources are materials obtained from nature. Natural resources
include plants, animals, fossil fuels (coal, oil, natural gas) and minerals.
Energy is needed to find natural resources, to separate them from other
materials like sand, soil, water and rocks, and to transport them to where
they are used by humans.
Activity: Natural resources from living things, air, Earth and oceans
1
Place the following natural resources in the appropriate column of the
table below: wool, oxygen, metal ore, salt, coal, wood, fish, natural gas
Living things
2
Air
Earth
Oceans
Now match these seven natural resources with the statements below
about the energy required to extract them.
a
b
c
d
e
f
g
Energy is used to fuel boats, sort, cut, freeze or dry, refrigerate and
transport _____________.
Energy is used to cool air to nearly –200°C to separate
__________.
Energy is used to drill, run pumps on pipelines and to liquefy
_____________ before exporting it from Australia.
Solar energy is used to evaporate sea water then diesel fuel is used
to operate bulldozers and trucks to collect _____________.
Energy is used to cut ____________, sort it, chemically remove
impurities and transport it overseas.
Energy is required to cut, dry, process and transport ___________.
Energy is used to discover, extract and separate ____________.
Check your answers.
Part 3: Using the energy concept
17
Made resources
Made resources are manufactured from natural resources.
The energy used to make made resources from natural resources has
changed with time.
Until about five thousand years before the present time (5000 BP) energy
for made resources mostly came from food used in human muscles.
Pyramids and other monuments, weapons, tools, dwellings, cloth and
cooking equipment were all made using human muscle energy. Heat energy
from burning wood or charcoal was used to make pottery and to extract
copper and lead from ores.
About 2300 BP moving water was used to move water mills that ground
grain to flour. Windmills started to be used for making flour and pumping
water about 1400 BP.
Two hundred and fifty years ago burning coal was used to run steam
engines. The movement from the steam engines was used to pump water out
of underground mines and to run machinery in the first factories.
Electrical energy has various sources over the last two hundred years:
200 BP
batteries transforming chemical energy to electrical energy
120 BP
windmills transforming kinetic energy to electrical energy
100 BP
coal burning electric power stations
50 BP
uranium using nuclear power stations produce electricity
30 BP
solar energy was transformed by solar cells to electrical energy
Electrical energy is the main energy used to produce made objects today.
Many objects that were made from natural resources one hundred years ago
are now made from synthetic materials.
Simple chemicals obtained from petroleum, coal and natural gas are built up
(synthesised) into new synthetic materials. Billiard balls are now made of
plastic rather than elephant ivory while lubricating oil now comes from
petroleum instead of whale blubber. Knife handles are plastic rather than
bone.
18
Energy
Fossil fuels
Fossil fuels such as coal, petroleum (oil) and natural gas have formed from
the remains of past life (fossils).
Predictions based on current rates of use and known reserves indicate that
Australia has enough:
•
coal for about 1 000 years
•
natural gas for about 100 years
•
petroleum for about 10 years.
Coal is burnt to provide heat energy for electric power stations (thermal
coal) and used to extract iron from iron ore (coking coal).
Natural gas can be used in gas turbine power stations when demand for
electrical energy is high (hot summer days and cold winter nights). Its main
use is for burning as a source of heat energy. Some natural gas is used to
make fertilisers and plastics.
Petroleum is separated into fractions such as petrol, diesel fuel and heating
oil. About 95% of the world’s petroleum is burnt as fuel. The other 5% is
used to make chemicals and synthetic products such as plastics and rubbers.
Non-renewable sources of energy
Non-renewable sources of energy are being used up and cannot be replaced
in a short period of time.
Fossil fuels are examples of non-renewable sources of energy. Once a fossil
fuel has been burnt (changing mostly to carbon dioxide and water) it is lost
forever.
Most of the fossil fuels used on Earth have formed in the last 300 million
years but humans may use them all up after about 300 years of use. Humans
are using fossil fuels up at a million times the rate at which fossil fuels are
formed! (Imagine how long your money would last if you spent it at a
million times the rate at which you obtained it!) This is why fossil fuels are
regarded as non-renewable sources of energy.
Another type of non-renewable energy is nuclear energy. Nuclear materials
have been around since the Earth formed 4.6 billion years ago. Uranium
could probably supply energy needs for thousands of years. Other forms of
nuclear energy, yet to be developed, might supply energy for tens or even
hundreds of thousands of years. However, nuclear materials suitable for
energy production would eventually be used up so nuclear energy is
regarded as a non-renewable source.
Part 3: Using the energy concept
19
Renewable sources of energy
Renewable energy is from sources that can be renewed, that is, used over
and over again.
Biomass
Material that can be obtained from living things is called biomass. Wood is
an example of biomass that can be burnt releasing energy.
If care is taken to replace the trees which are removed as wood, the energy
supply is renewed.
Other biomass can be changed into liquid or gas fuels. In Brazil a lot of the
sugar cane crop is used to make liquid ethanol which is used as a fuel for
cars instead of petrol. In some parts of Australia ethanol made from sugar
cane or waste from processing grains is mixed with petrol and sold at petrol
stations. Even waste cooking oil from fish and chip shops has been used in
some diesel engine vehicles!
Biogas is mostly methane gas obtained from the breakdown of sewage or
manure from pigs and chickens. The biogas can be burnt in air releasing
energy. Some sports fields built on landfill covering rubbish tips use biogas
methane to provide lighting.
Solar energy
The Sun is a star about half way through its lifetime. So solar energy should
be available for about another 4.6 billion years.
You may have a solar (also called photovoltaic) cell in a watch or calculator.
Solar cells are also used to provide electrical energy in isolated places such
as telephones in outback Australia. Space vehicles and satellites have solar
panels made up of solar cells to provide electricity.
Wind energy
Wind energy is the most rapidly increasing method of generating electricity
in Australia and the world. The large blade generators are placed on hills in
windy areas—some people call these tourist attractions while other people
call them visual pollution. Denmark generates more than 15% of its
electricity from wind.
20
Energy
Geothermal energy
Leaving out areas containing volcanoes, Australia has the hottest rocks in
the world near the border between South Australia and Queensland.
Temperatures of 250°C are easy to access. These hot rocks should remain
hot for tens or hundreds of millions of years.
Tidal/wave energy
Water moved by tides can be used to turn huge blades in water turbines.
Waves can be used to move air in tubes; the air moving back and forth in the
tubes can turn blades in air turbines. Movement of the turbines is transferred
to electrical generators that change kinetic energy to electrical energy. Huge
tides off NW Australia and waves near Wollongong are possible sources of
tidal/wave energy.
Hydroelectricity
Hydroelectricity changes the kinetic energy of water moving downhill into
electrical energy. The Snowy Mountains scheme and hydroelectricity plants
in Tasmania provide about 8% of Australia’s electricity. In wetter and more
mountainous countries such as Canada, Brazil and New Zealand over half
the electricity comes from hydroelectricity.
Electrical energy production worldwide in 2000
Type of electrical energy production
% worldwide
Coal burning
39
Natural gas burning
17
Hydroelectricity
18
Uranium in nuclear reactors
16
Oil burning
8
Wind, solar, geothermal, tidal/wave
2
Complete Exercise 3.3: Energy resources of Australia.
Part 3: Using the energy concept
21
22
Energy
Lesson 14: Energy technology
Technologies make tasks easier or more convenient. A technology can be as
simple as a sharp edge used for cutting or as complex as the worldwide
network of computers called the Internet.
Advanced technologies mostly use electrical energy. However only about
one third of the world’s population has a reliable supply of electricity.
Another third of the world is connected to electricity but their supply is
unreliable while the remaining third of the world’s population has no
electricity supply.
Nevertheless the world relies more and more on electrical energy. Electrical
energy is the most versatile energy source, easily changed to kinetic,
potential, light, heat, sound or chemical energy.
Activity: Energy transformations in everyday devices
List everyday devices that you have at home that change electrical energy to:
a) light energy
_________________________________________________________
_________________________________________________________
b) heat energy
_________________________________________________________
_________________________________________________________
c) sound energy.
_________________________________________________________
_________________________________________________________
Check y our answers.
Part 3: Using the energy concept
23
Energy transformations to electrical
energy
Do you have devices at home that can produce electrical energy?
You may have an outdoor light that uses solar energy collected by a solar
cell to run the light at night.
Some calculators and watches have small solar cell panels to change light
energy to electrical energy.
Many cars in the future will be equipped with electric motors as well as
petrol engines. Electrical energy produced by a generator run by the petrol
engine is stored in batteries and used to operate the electric motors in the
wheels. When maximum power is required both the petrol engine and
electric motors provide power. In city traffic the less polluting electric
motors only are used. When cruising the batteries are recharged by the
petrol engine. These vehicles will be able to halve the consumption of petrol
by cars.
Energy transfers in a ‘hybrid’ car run by petrol and electric motors
Energy technology using steam
Before electrical energy started to become widely available about a century
ago most energy used in factories and mines in the 1700s and 1800s came
from steam engines. Fuels such as wood or coal were burnt, water boiled
and the kinetic energy of the steam used to produce movement in machinery
or pumps.
Today most electric generators are turned by turbine blades which are
moved by the force of high pressure steam. The steam is made by boiling
water using heat released by burning coal, oil, wood or waste plant material
or even heat released in nuclear reactors from uranium.
To help you understand how heat energy from burning fuel could be used to
produce movement carry out the following activity.
24
Energy
Activity: Making a simple steam engine from a soda water can
What you need:
•
unopened can of soda water
•
spirit burner or candle at least 1 cm thick
•
matches
•
tray at least 4 cm deep, e.g. rectangular takeaway food container
•
pin or very small thin nail
•
thin string or thin rubber band at least 10 cm long
•
retort stand, bosshead and clamp
•
safety goggles
•
access to a sink.
What you do:
1
Don't open the can. Carefully rotate the puller so that it is over the place
where the hole appears when a can is opened.
2
Carefully bend the puller so that it is at right angles to the top of the
can. You should be able to hold this vertical puller section and freely
swivel the unopened can around the bent puller section.
Put your safety goggles on now. Soon you will make a small hole in the
unopened can with the pin. There could be a sudden pressure release that
suddenly moves the pin.
3 Place the unopened can in the tray to catch leaking soda water. Hold
the pin about half way down the side of the can. Holding the pin at
about 30° to the surface, make a small hole in the side of the can.
Now turn the can through half a turn (180°) and push the pin in the
same way to make a second hole about 30° to the surface but on the
opposite side.
Part 3: Using the energy concept
25
4
Put the can in a sink just above the sink hole. Shake the can so that jets
of soft drink come out the holes. The jets should come out at an angle to
the surface, not at right angles. The two jets should also stream out in
opposite directions.
When the can is about half empty put it on its side with one of the holes
down for another five minutes. You want most, but not all of the soda
water, out of the can.
5
Set up the retort stand, bosshead and clamp with the spirit burner/candle
on the stand base. Loop the string or rubber band through the hole in the
can puller so the equipment is like this:
Experimental set up
6
Adjust the equipment so that the bottom of the can is a few centimetres
above the top of the spirit burner/candle. Check that the can freely
swivels around the puller. Light the burner. Continue heating the can
for at least three minutes after its liquid contents start to boil.
7
Observe what happens to the can when the spirit burner/candle flame is
put out.
What you observed:
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
26
Energy
Activity: Matching changes as energy transfers or energy
transformations
Listed below are a number of changes that happened in this activity. Under
each change you are to complete either the energy transfer statement or the
energy transformation statement.
1
Match burning
_________ energy transfer from_________ to ___________ energy is
transformed to___________ energy
2
Spirit burner/candle flame heating liquid water in aluminium can
_________ energy transfer from_________ to ___________ energy is
transformed to___________ energy
3
Liquid water changing to gaseous water (steam)
_________ energy transfer from_________ to ___________ energy is
transformed to___________ energy
4
Steam jets coming from holes causing can to turn
_________ energy transfer from_________ to ___________ energy is
transformed to___________ energy
5
String or rubber band twisting as can turns
_________ energy transfer from_________ to ___________ energy is
transformed to___________ energy
6
String or rubber band unwinding after spirit burner/candle is put out.
_________ energy transfer from_________ to ___________ energy is
transformed to___________ energy
Check your answers.
Complete the Exercise 3.4: Most steam engines were not locomotives?
Part 3: Using the energy concept
27
28
Energy
Lesson 15: Using models, theories
and laws
How science works
Scientists work at science in many different fields and many different ways.
However, what they do often fits the following steps, and can be applied to
your everyday life.
Step
Everyday example
1
Identify a problem
My feet smell
2
Gather background information
Read about foot infections
3
Develop a hypothesis which can
be tested
If I keep my feet drier then there is
less chance of smelly infection
4
Identify variables and what
needs to be controlled
Wear the same type of socks and
shoes while keeping feet dry
5
Design an experiment to test the
hypothesis
For one week keep one foot dry
while the other is allowed to get wet
6
Make observations and collect
data
Sniff feet, socks or shoes to
compare. Record results for a week
7
Identify possible sources of
error in results
Don’t forget which sock or shoe
came off the left foot before
recording results
8
Come to a conclusion based on
data that supports or rejects the
hypothesis
Decide whether keeping a foot dry
reduces smelly foot
9
Communicate results and
conclusion.
Let members of your family (and a
friend?), know what you found out.
To understand and explain the results of investigations scientists have
developed models, theories and laws. This lesson reviews the particle
model/theory and the law of conservation of energy. These are two of the
most important ways of understanding how the world works.
Part 3: Using the energy concept
29
The particle model of matter
The particle model of matter assumes that matter is made up of particles that
are small, can vibrate around fixed positions, move freely over one another
or move at high speed. This model can be used to compare the three states
of matter.
State of matter
Volume property
Shape property
fixed
fixed
fixed
bottom of container
volume of container
whole container
Activity: Using the particle model of matter to explain states of matter
properties
1
Explain why a solid has a fixed volume and fixed shape.
__________________________________________________________
__________________________________________________________
__________________________________________________________
2
Explain why a liquid has a fixed volume but shape that is the same as
the bottom of its container.
__________________________________________________________
__________________________________________________________
__________________________________________________________
3
Explain why a gas has the same volume and shape as its container.
__________________________________________________________
__________________________________________________________
__________________________________________________________
Check your answers.
Now use the particle model to explain expansion and contraction. Modify
the simple model just used to explain solid, liquid and gas properties by
adding the concept of kinetic energy.
30
Energy
Activity: Using a modified particle model of matter to explain expansion
and contraction of solids and liquids
Solids expand when heated and contract when cooled. And so do liquids,
and so do gases. Use the concept of kinetic energy in the answers below.
1
Explain why a solid expands when it is heated.
_________________________________________________________
_________________________________________________________
2
Use the term kinetic energy to explain why a hot liquid contracts when
it becomes a cool liquid.
_________________________________________________________
_________________________________________________________
Check your answers.
A model could become a theory
If a model is successful it could become a theory.
A model is often changed. The new model is then tested to see if it is closer
to how the world works. If it is, the new model replaces the old model.
There are many models. Different scientists can develop slightly different
models. The models can be compared to find the best.
A theory is not changed as much as a model. A theory is agreed upon by a
number of scientists. The theory is changed only when there is good
evidence to change.
A theory must:
•
explain what has already been observed
•
predict what has not yet been observed
•
be able to be tested by further experiments or observations
•
be capable of being changed as required by new results.
In chemistry the particle model became very successful in explaining what
happened in reactions and in understanding the properties of chemical
substances. In physics mathematical equations for the particles were
developed to explain the properties of gases.
Part 3: Using the energy concept
31
The particle model is now often called the particle theory. Sometimes it is
called the kinetic molecular theory because it explains using the idea that
small particles (molecules) have different amounts of moving (kinetic)
energy.
The kinetic molecular theory for gases uses the following ideas:
1
Gases are made up of molecules (particles) with a lot of kinetic energy
moving at high speed.
2
The higher the temperature the higher the kinetic energy and speed of
the molecules.
3
When a molecule hits the wall of its container it exerts a pressure and
rebounds without losing energy. The total gas pressure is made up of all
the pressures exerted by all the molecules.
Activity: Using the particle theory of matter to predict changes in gas
pressure
1
Predict what happens to the gas pressure if more gas particles are put
into a container of gas. In other words, what happens if there are more
gas particles hitting the wall of the container?
_________________________________________________________
_________________________________________________________
2
Predict what happens to the gas pressure if the temperature of gas in a
container is increased. In other words, what happens if the gas particles
have more kinetic energy when they hit the wall? … and what happens
if the gas particles are moving faster and hit the walls more often?
_________________________________________________________
_________________________________________________________
3
Use the particle theory to explain why the gas pressure in a bike tyre
decreases if it leaks gas.
_________________________________________________________
_________________________________________________________
4
Use the particle theory to explain why the gas pressure in a bike tyre is
lower on a cold day.
_________________________________________________________
_________________________________________________________
Check your answers.
32
Energy
You have just used a simple particle model, a particle model using the
kinetic energy concept and finally the kinetic molecular theory.
Scientists usually use the simplest model or theory that can explain
observations. If this is unsatisfactory they might modify the model or theory
to better explain observations.
Theories and laws
A theory can be open to doubt. Sometimes predictions made using a theory
are not supported by an experiment or further observations. The theory may
have to be changed and a better theory developed.
In science theories are being discarded, modified and improved all the time.
A theory that may be useful now could be replaced by a better, more useful,
theory in a year or ten years time. So far the particle theory has proved very
useful and there is no other theory that could replace it.
If a scientific theory has survived every test it can become a scientific law.
A law is a law only if it works for every test and experiment.
There are not many scientific laws. The most important of all is the law of
conservation of energy. Energy cannot be created or destroyed. Energy just
undergoes transformations (changes from one form to another) or transfers
(like when heat transfers from one place to another). The total amount of
energy does not change.
This is the most important scientific law of all, applying in all sciences, all
the time and in all parts of the known Universe.
Complete Exercise 3.5: Designing a scientific investigation.
Part 3: Using the energy concept
33
34
Energy
Suggested answers – Part 3
Activity: Chemical formula – what does it stand for?
Chemical
Formula
Carbon
atoms
Hydrogen
atoms
Oxygen atoms
carbon dioxide
CO2
1
-
2
water
H2O
-
2
1
glucose
C6H12O6
6
12
6
Activity: Understanding a food web
a) rabbit, eagle, bandicoot, fox
b) rabbit, bandicoot
c) pasture grass, wild grass, tree
d) wallaby, like the rabbit, feeds on pasture grass and wild grass
e) eagles are higher up the food pyramid than rabbits and since only about
10% of the energy in rabbits would be transferred on being eaten by
eagles there must be many more rabbits than eagles (this assumes the
eagles do not mostly eat bandicoots).
f)
foxes
rabbits
pasture grass
Food pyramid
Part 3: Using the energy concept
35
Activity: Investigating energy transfer and energy transformation
1
The moving marble/round lolly stopped, losing its kinetic energy. The
marble/round lolly at the other end moves away with kinetic energy. A
click sound was heard as the rolling marble/round lolly hit the row of
marble/round lollies.
2
Kinetic energy was transferred from the rolling marble/round lolly to
the marble/round lolly at the other end of the row.
3
The click sound showed that some of the kinetic energy of the rolling
marble/round lolly was transformed to sound energy.
Conclusion
In an energy transfer, the same type of energy is transferred from one
location to another. This happened when the kinetic energy of the rolling
marble/round lolly was transferred to the marble/round lolly at the other end
of the row.
Activity: Classifying energy transfers and energy
transformations at home
Change
Transfer/transformation
Energy
operate an electric fan
transformation
electrical → kinetic
moving fan blade
moves air
transfer from blades to air
kinetic
toaster heats bread
transfer of heat rays from
element
heat
gas burns in heater
transformation
chemical → heat
turn on electric light
transformation
electrical → light
use microwave oven
transformation
electrical → heat
turn on radio
transformation
electrical → sound
use hot water bottle
transfer
heat
use battery
transformation
chemical → electrical
Activity: Calculating and comparing the energy efficiency of
microwave ovens
800
100
×
1200
1
= 66.7%
970
100
model 668 % efficiency =
×
1400
1
= 69.3%
model 726 % efficiency =
Therefore the model 668 is more efficient.
36
Energy
Activity: Natural resources from living things, air, Earth and
oceans
Living things
Air
Earth
Oceans
wool
oxygen
metal ore
salt
natural gas
fish
wood
1
Energy is used to fuel boats, sort, cut, freeze or dry, refrigerate and
transport fish.
2
Energy is used to cool air to nearly –200°C to separate oxygen.
3
Energy is used to drill, run pumps on pipelines and to liquefy natural
gas before exporting it from Australia.
4
Solar energy is used to evaporate sea water then diesel fuel is used to
operate bulldozers and trucks to collect salt.
5
Energy is used to cut wool, sort it, chemically remove impurities and
transport it overseas.
6
Energy is required to cut, dry, process and transport wood.
7
Energy is used to discover, extract and separate metal ore.
Activity: Energy transformations in everyday devices
a) Electrical energy to light energy
light globe, fluorescent light, television receiver, electric
torch/flashlight
b) Electrical energy to heat energy
All of the devices in part a also produce some heat energy as well as
light energy. The electric radiator, electric heater, electric stove/oven,
microwave oven, electric jug, electric toaster, heat lamp, electric hot
water service, any electric motor in any device changes some of its
electricity to heat.
c) Electrical energy to sound energy
television receiver, radio receiver, tape/CD/DVD player, electric bell,
smoke alarm, fire alarm, burglar alarm, telephone
Activity: Matching changes as energy transfers or energy
transformations
1
Match burning
chemical energy is transformed to heat (and light) energy
2
Spirit burner/candle flame heating liquid water in aluminium can
heat energy transfer from gaseous flame to liquid water (through the
solid aluminium)
Part 3: Using the energy concept
37
3
Liquid water changing to gaseous water (steam)
heat (or kinetic) energy transfer from liquid water to gas
4
Steam jets coming from holes causing can to turn
kinetic energy transfer from steam to can
5
String or rubber band twisting as can turns
kinetic energy is transformed to potential energy
6
String or rubber band unwinding after spirit burner/candle is put out.
potential energy is transformed to kinetic energy
Activity: Using the particle model of matter to explain states of
matter properties
1
The particles in a solid are close together, touching one another in a
regular arrangement, occupying a fixed volume and having a fixed
shape.
2
A liquid has a fixed volume because the particles are touching one
another. A liquid takes up the same shape as the bottom of its container
because the particles are free to move over one another.
3
A gas has the same volume and shape as its container because the gas
particles move freely at high speed and fill every part of the container.
Activity: Using a modified particle model of matter to explain
expansion and contraction of solids and liquids
1
A solid expands when it is heated because the solid particles have more
kinetic energy, vibrate more around their fixed positions and take up
more space.
2
A hot liquid contracts when it becomes a cool liquid because it has lost
kinetic energy. The liquid particles move less and move in a smaller
space.
Activity: Using the particle theory of matter to predict changes in
gas pressure
38
1
The gas pressure is the total pressure of all the gas particles hitting the
wall of the container. Doubling the number of gas particles would
double the number of hits and double the gas pressure.
2
If the temperature of gas in a container is increased the particles will
have more kinetic energy. The particles will exert a greater pressure
when they hit the wall and they will hit the wall more often because
they are moving faster. This causes the gas pressure to increase.
3
The gas pressure in a bike tyre decreases if it leaks gas because fewer
particles are hitting the inside wall of the tyre to produce pressure.
Energy
4
The gas pressure is lower on a cold day because the particles have less
kinetic energy and hit the inside wall of the tyre with less pressure and
less often.
Part 3: Using the energy concept
39
40
Energy
Exercises – Part 3
Name: ____________________________________________________
Teacher: __________________________________________________
Exercise 3.1: How well do you understand food
pyramids?
You can check your understanding of food pyramids by answering these
questions.
1
Consider this food chain:
cabbage leaves → caterpillar → lizard → snake
a) In the space below, draw a food pyramid to represent this food
chain.
b) Can you see that the arrows in the food chain could represent three
different ideas?
What information do the arrows give about:
i. what eats what? __________________________________
ii. numbers of living things? __________________________
iii. energy? ________________________________________
c) Does your food pyramid show that there are more lizards than there are
snakes in this community? Explain.
_________________________________________________________
_________________________________________________________
Part 3: Using the energy concept
41
d) How would the other organisms in the food chain be affected if all the
caterpillars were killed?
_________________________________________________________
_________________________________________________________
42
Energy
Exercise 3.2: Energy ratings of electrical appliances
Samples of energy labels can be seen in shops or at the web site
<http://www.energyrating.gov.au> This website is Australia’s leading guide
in choosing an energy efficient appliance.
There are two types of labels:
•
Energy rating labels show the energy efficiency using a star rating (six
stars is the most energy efficient). These labels must be on all new airconditioners, clothes dryers, clothes washers, dishwashers and
refrigerator/freezers sold in Australia
•
Energy endorsement or top energy saver awards (TESAW) introduced
in 2004. Awarded to the most energy efficient models on the market in
their class at the time of testing.
Energy ratings of electrical appliances are available to help Australians take
responsible actions and buy more energy efficient appliances. This can
reduce the amount of greenhouse gases such as carbon dioxide released to
the atmosphere by power stations. Many scientists think that increase in
greenhouse gases is causing changes in the Earth’s climate.
Seek out the two types of labels in a shop or go to:
<www.energyrating.gov.au/rac3.html> and
<www.energyrating.gov.au/tesaw-main.html> to see the labels. Then,
answer the questions below:
1
Who runs this program of providing scientific information?
_________________________________________________________
2
What does the power abbreviation kW represent?
_________________________________________________________
3
Why do some airconditioner labels have two sets of star ratings?
_________________________________________________________
4
Where do you go for more information?
_________________________________________________________
5
Note down the make and model name/number for an air conditioner,
clothes dryer, clothes washer, dishwasher or refrigerator/freezer. Find
out its energy rating.
Appliance type
Make
Model name/number
Energy rating
Part 3: Using the energy concept
43
Exercise 3.3: Energy resources of Australia
The map below shows important energy resources of Australia.
Timor
gap
Ranger
mine
North west
shelf
Bowen
basin
Roxby
downs
Leigh
creek
Cooper
basin
Hunter
valley
Collie
Snowy
mountains
Latrobe
valley
Bass strait
Tasmanian
highlands
Important energy sources in of Australia
Complete the table following by writing in the last column whether the
resource is non-renewable or renewable.
44
Energy
Location
Resource
Leigh creek
black coal
Collie
black coal
Bowen basin
black coal
Hunter valley
black coal
Latrobe valley
brown coal
Bass strait
petroleum
Bass strait
natural gas
North west shelf
natural gas
Timor gap
natural gas
Cooper basin gas field
natural gas
Cooper basin hot rocks
geothermal
Ranger mine in Kakadu
uranium
Roxby downs mine
uranium
Snowy Mountains
hydro
Tasmanian highlands
hydro
Part 3: Using the energy concept
Renewable/nonrenewable
45
Exercise 3.4: Most steam engines were not
locomotives
Use research tools to find information. For example, you may need to use a
library, an encyclopaedia, the Internet or ask people around you.
A steam engine is a machine that uses steam to produce useful movements.
The first steam engines did not haul trains on rails. Steam engines attached
to trains on rails are best called steam locomotives.
1
Hero, a Greek who lived in the Greek city of Alexandria in present day
Egypt nearly two thousand years ago, is often credited as the inventor
of the first steam engine.
Use research tools to find information about Hero’s steam engine.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
2
Compare (show how things are similar or different) Hero’s engine and
the simple steam engine you made from a soda water can.
Similarities:
_________________________________________________________
_________________________________________________________
Differences:
_________________________________________________________
_________________________________________________________
3
The oldest surviving rotating steam engine in the world, still capable of
working, is in Sydney’s powerhouse museum. Find out how this famous
stationary steam engine ended up in Sydney at:
<http://www.powerhousemuseum.com/exhibitions/boulton&watt.asp>
_________________________________________________________
_________________________________________________________
_________________________________________________________
46
Energy
Exercise 3.5: Designing a scientific investigation
Here is an opportunity for you to design a scientific investigation. Your
course requires you to carry out at least one substantial research project
during Stage 4 (Years 7 and 8). This exercise enables you to plan how you
could work the way scientists do.
You are not to carry out the investigation, just set out your ideas.
Step
1
Identify a problem
2
Gather background
information
3
Develop a hypothesis
which can be tested
4
Identify variables and
what needs to be
controlled
5
Design an experiment to
test the hypothesis
6
Make observations and
collect data
7
Identify possible sources
of error in results
8
Come to a conclusion
based on data that
supports or rejects the
hypothesis
9
Communicate results and
conclusion
Part 3: Using the energy concept
My possible scientific investigation
47