Developed
by Jonathan Osborne. Sc4, Forces
King’s College, University of London
Introduction
This activity is based on a version of a well known thought experiment
originally developed by Galileo. Thought experiments have an important
role in science as they lay out a series of ideas about how the
world should behave. Examining the argument critically is an important
task to see where fallacies might exist. If they cannot be found
to exist, then this demonstrates a fundamental idea in science
– that we believe in ideas until they are refuted. Sir Karl
Popper first advanced this idea in the first half of the 20th
Century.
The activity asks pupils to provide a written argument for their
choices. Justifying reasoning and linking an idea to the evidence
that supports it is central in science. Pupils’ writing, however,
needs to be supported and this activity uses a writing frame.
Objective
Pupils will learn
• to consider and evaluate scientific arguments;
• to develop arguments in writing;
• about a key scientific idea.
Outcomes
By the end of the lesson, pupils will be able to:
• explain using scientifically sound ideas, why, in the
absence of air, all objects fall at the same rate;
• evaluate different scientific arguments;
• communicate their arguments in written form.
Notes for Teachers
Pupils will need to know that forces are measured in Newtons and
that the pull of gravity is a force that acts on all objects.
Teaching Sequence
• Begin by posing the question, ‘Do heavier things fall
faster?’ and asking each pupil to write down his or her answer.
Ask them to give any reasons that they can think of for their answer.
• Ask the pupils to share their views with the person next
to them.
• Now demonstrate with a 1kg mass and a 1p piece (make
sure that they drop into a tray of sand to minimise the damage
to the floor). This process is likely to expose that most people
think that ‘heavier things fall faster’. The demonstration
will challenge that idea and the task offers an opportunity to
provide some reasons for what they have just seen.
• Hand out the ‘Do heavier
things fall faster?’ sheet and explain that their
task is to examine the argument that heavier things do not fall
faster than lighter ones. Tell them that the argument is presented
in steps. For each step, they must decide whether it is true or
false. Then, they must use the space beneath to justify their
choice.
• Whilst they are doing this task, circulate and find one
or two examples of a better quality answer which can then be read
out so that the class gets a better sense of what they are being
asked to do.
• Let them work in pairs on all of the steps of the argument.
Remind them that they must choose true or false and that they
MUST provide reasons for their choice as scientists do.
• Then let the pairs join with another pair (‘pairs’
to ‘fours’) to share their answers and reasoning.
• Finish by holding a class plenary. Go through each step
asking ‘Who want to argue that this is TRUE?’ and
elicit one or two arguments. Then ask ‘Who wants to argue
that this statement is FALSE?’ and, likewise, elicit one
or two arguments. You will have to resolve the argument by pointing
to what the scientific case is. Point out that it is irrefutable
which is why we believe it.
• A suggested homework activity is provided (pupil activity
sheet 2).
Pupil Activity Sheet 1: Examining a scientific argument
Do heavier things fall faster?
Lots of people think that heavier things fall faster than lighter
ones. We see it around us every day – the feather reaches
the floor after the brick and a piece of paper flutters slowly to
the ground. But is this always true?
Consider each of the following steps of the argument. For each
step, decide whether it is TRUE or FALSE. Give reasons to justify
your choice.
| Step 1:
The weight of an object is the force of the pull of gravity
on an object.
This is TRUE FALSE
Reasons to justify choice
_____________________________________________________________________________________________________________________
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|
| Step 2:
The pull of gravity on a 2kg object is twice that on 1kg object.
This is TRUE FALSE
Reasons to justify choice
_____________________________________________________________________________________________________________________
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|
| Step 3:
The rate at which an object accelerates (speeds up) depends
on the force on it and how big it is. So a 2kg object will
speed up more slowly than a 1kg object if the same force is
applied.
This is TRUE FALSE
Reasons to justify choice
_____________________________________________________________________________________________________________________
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|
| Step 4:
A 2kg object has twice as much force acting on it as a 1kg
object. But, there is twice as much matter to speed up. So,
if twice as much force acts on the 2kg object, it will speed
up (accelerate) at the same rate as a 1kg object. The result
is that it will hit the ground at the same time.
This is TRUE FALSE
Reasons to justify choice
_____________________________________________________________________________________________________________________
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|
| Step 5:
If you think that this argument is true – then why?
a) Does this argument also apply to feathers?
b) Why do you think that so many people believe that heavier
things fall faster?
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Pupil Activity Sheet 2: Examining a scientific argument
Examining a scientific Argument:
Imagine that a brick is dropped from an aeroplane, flying at a height
of 1000 metres. It falls to the ground. The statements in the boxes
below link together to explain how the brick falls.
Some boxes contain more than one statement. In each of these
boxes, pick the statement that you think is correct, and fits
into the whole explanation. Indicate your choice by putting a
line through the other statement(s) in the box.
