Forensics fake problem
Murder by the sea
Giles Redhill was found dead in his study at 10:40 am. His cook has reported hearing shots fired
at 10:30 am. Statements have been taken from all guests staying at the house.
There are three suspects. Each one has a witness to say where they were at 10:20 am but each
would have had time to enter the house and shoot Giles.
Rose Redhill was
spotted sunbathing
on Sandy Cove.
Poppy Potter
was spotted
in the garden
painting
the new
summerhouse.
Stairs to
Sandy Cove
house
Daisy Duke was spotted swimming
in the sea off Pebble Beach
© Association for Science Education and Centre for Science Education 2010
Forensics fake problem
The evidence
The evidence
When the forensics team arrived, they
examined Giles’s study and found small
patches of what looked like white powder
dotted over the floor.
Identify the substances on the soles of
Poppy’s and Rose’s shoes. Say whether
they are a solid, liquid or gas.
Examination under a microscope revealed this
to be made of small white crystals.
Use your understanding of how particles
move to explain why the white liquid had
spread over parts of Daisy’s shoes
whereas Rose’s shoes just had tiny specs
of crystals that had not spread.
Forensics asked to see the shoes that the
three suspects had been wearing that
morning.
Their observations are below:
Shoe
Observations
Poppy
Potter
Top of shoes covered with
large patches of a white sticky
liquid.
Rose Redhill
Tiny crystals of various colours
(yellow/brown/white) on the
bottom of the shoes.
Daisy Duke
Was not wearing shoes this
morning.
© Association for Science Education and Centre for Science Education 2010
DS Sharon Fletcher immediately rules Poppy
and Rose out of her enquiries.
However, she is puzzled. If Daisy had run
barefoot straight from swimming in the sea
you would expect to find drips of seawater on
the floor of the study.
Use the idea of particles to explain where
the seawater has gone, where the white
crystals left on the study floor came from,
and why they appeared.
Forensics fake problem
Teachers’ guide
Goal
The problem targets understanding part of the
Big Idea: Particles.
 A model may be used to describe solids,
liquids and gases as being made up of very
many tiny particles.
 Particle theory may be used to explain the
physical properties of solids, liquids and
gases.
 It can also be used to explain changes such
as dissolving, heating and cooling and
changes in terms of the particle model.
 The particle model can also explain how
separation techniques can separate
mixtures.
APP links
The problem could be used to assess
achievement against criteria in the
‘Explanations’ strand of AF1.
Marking guide
APP L3
Use straightforward scientific evidence to answer questions.
• Correctly identifies the substance on Rose’s shoes as sand and states
that it is a solid.
• Correctly identifies the substance on Poppy’s shoes as paint and states
that it is a liquid.
APP L4
Uses scientific ideas when describing simple processes or phenomena.
 Uses the idea of particles to explain that the particles in the crystals of
sand cannot move position (although they will be in constant motion in
a fixed position) and therefore the crystals cannot spread or flow.
 Uses the idea that particles in a liquid can move position to explain
that once a drop of paint lands on Poppy’s shoes it can flow and
spread out.
APP L5
Uses abstract ideas or models or more than one step when describing
processes or phenomena.
 Describes seawater as containing dissolved salt and describes this in
terms of the salt being divided into very small particles that can then
mix in between the water particles
 Explains that as the drips of seawater warm up the water particles
move faster until eventually they spread out so far that they become a
gas (water vapour).
 The drips of seawater had therefore dried before the forensics team
got to the scene leaving just the crystals of salt that had been
dissolved in the water.
Note: if there is evidence for more complex thinking in the student’s
answer that uses knowledge that has not been taught then a level 6
can be awarded.
© Association for Science Education and Centre for Science Education 2010
Picture credits
Picture
Slide
Credit
Assessment from the Forensics unit © Association for Science Education and Centre for Science Education 2010. Teachers and others who
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© Association for Science Education and Centre for Science Education 2010