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This activity explores the nature of
a good scientific explanation.
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| Overview of the activity |
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Explanations are
a key focus of science. This activity, which develops
an activity used previously at KS3, and published
by SEP as part of materials on Teaching
about Ideas and Evidence in Science at KS3,
was used in ASCEND to encourage students to think
about one feature of the nature of science, by considering
the characteristics of a scientific explanation.
The aim of the session was to help students
a) appreciate that explanations play a central role
in science
b) to have criteria for ‘good scientific explanations’:
in science explanations are expected to |
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i) be logical
ii) be based on evidence and/or accepted
scientific ideas
iii) usually be consistent with accepted
scientific knowledge
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| The session includes
two activities. The first involves students working
in pairs forming their own explanations for phenomena,
and then swapping their explanations with another
pair. The second activity involves evaluating a
mooted set of explanations. The first activity is
intended to provide students with an engaging activity
that will get them thinking about explanations,
and (by working with the explanations from another
pair) and considering what makes a good explanation.
The second activity reinforces this by asking students
to evaluate mooted explanations. |
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| Rationale for the activity |
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| It is intended to use
the two activities within the same session if sufficient
time is available (i.e. the ASCEND sessions were
90 minutes long). However, the activities could
be used in two successive sessions if less time
is available for a session. |
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| 1. Introducing scientific
explanations: ‘suggest an explanation’ |
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The first activity is designed to
get students discussing possible explanations, and
so provide a starting point for thinking about what
a good explanation might be in the context of specific
target phenomena. This activity is based around
a large set of invitations to suggest an explanation
for various phenomena. Although students may well
know accepted explanations for some (from school,
or informal science learning) the set was designed
to include a wide range of phenomena for which most
students would not have a ready-made explanation.
It was known from using this idea in school with
a top set Y9 (13-14 year old) science group, that
most able students found this to be an enjoyable
activity and that the choice of phenomena
to explain had been appreciated.
The activity has been developed for use with most
able KS4 (14-16 year-old students). In the version
of the activity used in ASCEND and included on the
CD here, students work in pairs to suggest explanations
– discussing the merits of their ideas, before swapping
their responses with another pair, and offering
each other feedback on the strengths and weaknesses
of their ideas. |
The set of questions provided has been designed
to:
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Cover a wide range of topics;
• Include some examples unlikely to have
arisen in science lessons;
• Offer some questions that can have explanations
at different ‘levels’ of explanation;
• Include questions intended to encourage
students to think ‘out of the box’. |
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| It is certainly not
expected that students will know current scientific
explanations for all the phenomena. The aim of the
exercise is to give a context for thinking about
the characteristics of a good scientific explanation,
rather than whether students can recall explanations
they have learnt. |
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| Some of the ‘explanations
wanted’ (there are 50 in the set) were for: |
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•
Why is sea water salty?
• Why don’t people lay eggs?
• Why does salt dissolve in water?
• Why do elastic bands stretch?
• Why do people have hairy armpits?
• Why are there 24 hours in a day?
• Why are only 3 elements (iron, nickel
& cobalt) strongly magnetic?
• Why don’t insects have lungs?
• Why do people age?
• Why do acids turn indicators red?
• Why don’t fish have arms?
• Why do we each have 2 nostrils?
• Why do knees only bend one way? |
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Clearly it is unreasonable
to expect secondary students to have scientifically
valid understandings of (for example) the origins
of ferromagnetism: but such questions have been
included as an opportunity for students to think
around issues, and explore their understanding (in
a way that may not commonly happen within the confines
of GCSE classes). Attempting to explain something
like the absence of lungs in insects can clearly
link to a range of relevant school science ideas.
Teachers should not be concerned if they feel they
can not offer satisfactory explanations in response
to some of these ‘why’ questions: nor can the author
(it being easier to pose than answer such questions!)
It is considered here that it is very important
that students do not get the impression that science
is about closed questions, and all the major puzzles
already have answers. (Such a view is likely to
discourage the most curious from looking to science
as a career direction.)
Some questions may certainly be seen form different
perspectives. An explanation for there being 24
hours in a day could either be about why the earth
takes the time it does to spin, or about why the
day would be divided into 24 equal periods (rather
than say 10 or 100 or 25).
Most questions can be answered at several different
levels of understanding, and this is important in
coming to understand the qualities of a scientific
explanation. So, for example, the sea is salty because
it contains a lot of dissolved salt, and salt dissolves
in water because it is soluble. These are explanations
in a sense, but do not help us understand the phenomena
much better. Indeed, using a label such as ‘soluble’
is little more than a tautology (in responding to
that particular question) if that is simply how
we label substances that dissolve in water. These
type of responses invite a further ‘but why?’.
Similarly, to say that humans do not lay eggs
because they are mammals is pretty limited in explanatory
terms – but sadly may well reflect just the kind
of answers we are training students to provide in
school science!
Many students seem not to have the ‘epistemic hunger’
of wanting to take explanations further: but this
is one area where we should expect the gifted to
persevere until they are satisfied they understand
a question.
A question such as why our knees only bend in
one direction clearly has several possible
types of answers. It can be answered in terms of
anatomy and physiology: the structure of the joint,
and the functions and properties of bone, muscle,
tendons etc. It also has a developmental answer:
how bodies grow to work that way. And, as always
in biology, there is the evolutionary explanation
– why we have evolved to have such a joint (which
is clearly different in nature to the hip joint)
in that position.
Even scientists may be criticised for sometimes
presenting ‘evolutionary just so stories’ – explanations
for how and why certain traits or structures have
evolved based on what seems feasible rather than
deriving from a strong evidence base. It is useful
for students to learn to appreciate how feasible
explanations, consistent with what we know, may
turn out to be refuted as further evidence comes
to light. |
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| 2. ‘Good’ and ‘poor’ scientific
explanations |
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The second activity
is one that had previously been found challenging
by top-set Y9 students. This involves the students,
working in groups, considering a set of prepared
explanations (many designed with specific flaws
– some more subtle than others) and selecting examples
of good and poor scientific explanations.
This is a high level activity according to the taxonomy
of thinking skills (see Chapter 3). The students
are asked to give their reasons why particular explanations
are judged to be poor. For this activity, the students
are provided with some suggestions about what makes
a good or poor scientific explanation. Teachers
may decide to only allow students access to this
support material after they have spent some time
working on the exercises based on their own ideas.
The main resource for this activity is a set of
mooted ‘explanations’ of various scientific worth,
for students to critique. ( The materials also include
templates for photocopying as A3 sheets for answering
the exercise.) |
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| Magnesium oxide
is produced when magnesium is burnt in air
as burning is a chemical reaction with oxygen. |
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Example 1: Why is magnesium oxide produced |
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‘if
I suddenly created a new science with all
. . . terminology . . . okay, say you’ve
never heard of a window . . . say . . .
you don’t know what a surface is . . . and
you start talking about surfaces . . . say
you start talking about . . . say you don’t
know what evolution is, and you start talking
about evolution, that’s all very well. But
you – don’t – know – what – evolution –
is, so you’d have to know the context for
it to be good science. If we assume they
know the context . . . if we assume they
know what an oxide is, that they know .
. . what magnesium is, that they know what
burning is and chemical reactions and things
. . . because . . . who are you explaining
to . . . ?’
(An ASCEND delegate considers the importance
of audience in judging an explanation) |
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As with most of the ASCEND activities,
there is plenty of scope for individual teachers
to modify the set – perhaps by adding some of their
own examples (especially useful to highlight dubious
explanations that have arisen in class, or to focus
thinking on recent topics.)
The set of explanations is designed to include examples
of common types of flaws in arguments, as well as
more sound examples. It is important to note that
although some of the examples are clearly ‘wrong’
from a scientific viewpoint, others offer various
degrees of sophistication. |
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| A lever can
be used so that a small force moves a large
weight, thus using less energy than moving
the weight directly. |
Example 2: An explanation
that contradicts scientific principles |
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| We always see
lightning before hearing the thunder because
the lightning sets off a process in the cloud
that builds up to a thunder rumble. |
Example 3: A feasible
explanation that is inconsistent with scientific
knowledge |
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Although the activity
asks students to identify examples of good and poor
scientific explanations, and justify their choices,
it is not intended that students come to think that
explanations are either good or poor.
As with most of the ASCEND activities, the final
outcome is less important than the process of debate
and argument through which students explore the
activity.
For example, the following explanation is logical: |
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| The apparent
movement of the stars through the night sky
suggests that either the earth spins round,
or that the rest of the universe rotates around
the earth. |
Example 4: A thought-provoking
explanation |
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| That the former option
(the spin of the earth) is currently accepted in
science does not make the other possibility logically
incorrect – although application of Occam’s razor
suggests that the movement of the earth is a better
option, as it is a simpler explanation. Gifted students
(especially pedantic ones) could point out other
logical possibilities: the stars revolve within
an otherwise fixed universe; some sort of field
around the earth deflects light from the stars in
such a ways as to give the appearance of relative
motion… For the purpose of this activity, exploring
the strengths and weaknesses of explanations is
more important than knowing which explanation is
currently believed correct. |
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| Scaffolding for
students |
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| Teachers using these
activities will need to decide how much help in
the way of hints and suggestions to give students,
and at what points to provide any support. The resource
materials on the CD offer two useful sheets. One
offers guidance on what an explanation is in relation
to other key ideas (see the figure). This sheet
may also be useful in supporting some of the other
ASCEND activities that discuss laws and models.
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Some
ideas about Science
Science is about understanding
(making sense of) the world (i.e.
the universe in which we exist,
not just the earth).
We try to understand the world
by developing theories
that enable us to explain what
happens, and what might happen
in the future (under various conditions).
An explanation is an answer to
a ‘why’ question. A scientific
explanation uses scientific ideas
(such as theories) to answer questions.
A theory is a way of explaining
the relationship between different
things. Theories are developed
by scientists in response to their
observations.
Information collected during observations
and experiments are called data.
When we observe a regular pattern
in our data, we sometimes call
this a ‘law of nature’.
Before scientists can carry out
an experiment, they must already
have an idea of what the relationship
might be.
An idea about a relationship that
has yet to be tested is called
a hypothesis. To test a
hypothesis scientists must design
an experiment and predict
what the outcomes would be if
the hypothesis is correct. There
are always lots of possible hypotheses
that could explain any observation,
so an experiment can never prove
a hypothesis is the correct one.
Experiments are subject to
errors.
Scientists often try to simplify
what they are studying by making
models. |
Figure 4.1: Information
provided for students |
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| Finding flaws in
explanations |
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| The second guidance
sheet included offers ideas on evaluating explanations
in science. The students are informed that an explanation
may: |
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seem logical, but not actually answer
the question asked
• seem logical, but be based on false
information or use principles that scientists
do not accept
• be illogical, so that the steps in the
explanation do not follow on from each
other
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| Some of the explanations
included in the examples for students are sound,
but may require some thinking though. |
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| It takes the Earth
about 23 hours and 56 minutes to turn once
on its axis compared with the distant stars.
However, because the Earth orbits the Sun
as well as spinning on its axis, it needs
to turn further before it faces the same way
compared to the sun. Each day the Earth moves
about 0.25% around its orbit, and so the Earth
needs to turn for an extra 4 minutes (0.25%
of a day) to return the same face to the Sun.
One day is therefore taken to be 23 hours
56 minutes + 4 minutes = 24 hours. |
Example 5:
A sound scientific explanation |
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| Others may be best considered
partial explanations. For example, the albedo of
Venus (about 65%) is higher than Pluto (about 40%),
so the following explanation ‘makes sense’. |
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| The planets
reflect the sun’s light, but some planet surfaces
reflect a larger proportion of the light reaching
them. Pluto is much less bright in the sky
than Venus because Pluto’s surface reflects
a smaller proportion of the sun’s light. |
Example 6: An incomplete explanation |
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However, such an explanation
is - at best - partial. Pluto is much smaller than
Venus (about a fifth the diameter), so has less
surface reflecting; is much farther from its source
of illumination (about 50 times as far from the
sun), and is much farther from us as observers.
The difference in albedo is a fairly minor factor
by comparison.
The students are also provided with some examples
of common types of flaws that may be found in ‘scientific’
explanations: |
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•
re-labelling – giving an explanation which
is just a renaming of the thing to be
explained
• tautology – when the thing to be explained
is assumed in making the explanation
• anthropomorphism – when human feelings
and motives are used to explain the activity
of non-humans
• animism – when inanimate objects are
treated as if they were living
• teleology – explaining in terms of objects
and processes having some purpose
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| A number of the examples
of mooted explanations provided demonstrate these
types of flaws. |
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| metal objects
will often ‘ring out’ when struck, because
metals are sonorous. |
Example 7: An ‘explanation’ that simply labels the
phenomenon to be explained |
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| Electrical
appliances are often ‘earthed’ as a safety
precaution in case any wires become disconnected
inside. The earth connection protects people
from electrocution as the charge wants to
travel to earth through the easiest path. |
Example 8: An explanation that uses anthropomorphism |
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| There was very
little oxygen in the atmosphere of the early
earth, and only very simple life was possible.
The oxygen in the air is mostly a by-product
of living things. Organisms evolved that produced
oxygen so that more complex animals and plants
would be able to evolve. |
Example 9: An explanation that is teleological:
suggesting that nature has a purpose |
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| Resources |
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| The following resources
are included on the CD: |
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| Resource |
Description |
Filename |
| Instructions
for ‘suggesting explanations’ |
Instructions
for first activity: groups of
4 students to work in pairs on
developing and then offering feedback
on explanations |
Act
4 Instructions 1 |
| Suggest
an explanation |
A
set of invitations to explain
a range of phenomena – students
select from these for the first
activity |
Act
4 suggest |
| Ideas
about science |
A
simple ‘one side of A4’ introduction
to some key terms in science –
explanations, and how these relate
to theories, laws, data and hypotheses. |
Act
4 Ideas about science |
| Explanations
about science |
A
‘one side of A4’ introduction
to explanations in science, including
criteria for judging explanations. |
Act
4 Explanations about science |
| Spotting
the flaws in explanations |
A
‘one side of A4’ summary of common
flaws in explanations, including
tautology and teleology. |
Act
4 Flaws |
| Instructions
for ‘judging explanations’ |
Instructions
for the second activity: evaluating
examples of prepared explanations |
Act
4 Instructions 2 |
| Explanations
to judge |
A
set of explanations of variable
scientific value for students
to critique and evaluate |
Act
4 to judge |
| Good
explanations |
Sheet
to be produced A3 size for students’
selected examples of good scientific
explanations |
Act
4 good |
| Poor
explanations |
Sheet
to be produced A3 size for students’
selected examples of good scientific
explanations |
Act
4 poor |
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| Download
PDF of activity 4 brief |
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