Triple Science case study
Physics
Name of centre
Ravens Wood School
Name of teacher
Jacqui Hopkinson
Subject
Physics
Specification
AQA
Brief description of case study
This introduces the idea of momentum through practical demonstration, student
experiment and analysis of measurements.
Disclaimer
It is important that the content of this case study is your own work and cannot be
attributed to any other source (eg a published scheme of work). Please confirm that this
is your own work by signing below.
Signed: Jacqui Hopkinson
Date: 16 October 2008
Page 1 of 9
Topic
Range and content
The principle of the conservation of linear momentum; that it is a vector quantity and
how the principle can be used to explain collisions
How Science Works
1.1 Data, evidence, theories and explanations
Pupils should be taught:
a how scientific data can be collected and analysed
b how interpretation of data, using creative thought, provides evidence to test ideas and
develop theories
c how explanations of many phenomena can be developed using scientific theories,
models and ideas
1.2 Practical and enquiry skills
Pupils should be taught to:
b collect data from primary or secondary sources, including using ICT sources and tools
Extract from Key stage 4 programme of study: http://curriculum.qca.org.uk/key-stages-3-and4/subjects/science/keystage4/index.aspx
Context of the lesson within scheme of learning
Students would previously have encountered Newton’s laws. Later they will use the
principles of the conservation of linear momentum to describe and explain a range of
contexts.
Learning objectives
• Know the equation for momentum and be able to work out the momentum of an
object travelling at different velocities.
•
Understand the concept of conservation of momentum and its significance in
calculating velocities. (Extension: understand that the conservation of momentum is
a necessary consequence of Newton’s third and second laws.)
•
Recognise the significance of the fact that velocity is a vector by using this to explain
the case of explosions.
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Learning outcomes
Students will be able to:
• state the equation for momentum and be able to work out the momentum in a range
of situations
•
•
•
(most students) explain that in a collision the total momentum after is equal to the
total momentum before the collision
(most students) use the law of conservation of momentum to work out the final
velocity of vehicles that stick together
(some students) work out the final velocity of vehicles in more complicated situations
and understand that this is a necessary consequence of Newton’s second and third
laws.
Key concepts/knowledge/skills/understanding addressed by this lesson
• A qualitative idea of momentum – a feel for it. A quantitative definition of momentum.
The idea of conservation of momentum, and how to use it to calculate velocities of
objects after collisions, including recoil velocities
• Analysis of experimental data can answer questions and help us to understand the
physics of a situation
Curriculum opportunities
X
a Research, experiment, discuss and develop arguments.
b Pursue an independent enquiry into an aspect of science of personal interest.
c Use real-life examples as a basis for finding out about science.
d Study science in local, national and global contexts, and appreciate the
connections between these.
e Experience science outside the school environment, including in the workplace,
where possible.
f Use creativity and innovation in science, and appreciate their importance in
enterprise.
g Recognise the importance of sustainability in scientific and technological
developments.
h Explore contemporary and historical scientific developments and how they
have been communicated.
Other curriculum opportunity from specification (give details):
Extract from Key stage 3 programme of study: http://curriculum.qca.org.uk/key-stages-3-and4/subjects/science/keystage3/index.aspx?return=/key-stages-3-and-4/subjects/science/index.aspx
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How Science Works progression in this lesson
The aspect of How Science Works being developed is:
•
Interrogation of raw data can help us to understand and make predictions about the
world.
How are students making progress?
In the past students have been encouraged to draw graphs with data. In this experiment
it is more appropriate to manipulate the data mathematically to find patterns and
equalities. They can then predict what will happen in other situations.
Assessment opportunities in this lesson
In the starter the teacher can see how many of the class have a general feel for the idea
of momentum and its connection to mass and velocity. During the starter practical the
teacher will be asking questions like ‘Which would be harder to stop, a mini or a lorry, if
they were both going at 30mph?’
During the main experiment the questions will relate to the conservation of momentum:
‘If I crash this cart into a cart of the same mass which is still, and they stick together,
what will their speed be afterwards? (Same, more, less, half, double?) To help ensure
that you can assess understanding across the whole class, ask students to write their
answers on mini whiteboards and hold them up.
How ICT is used to support learning
This lesson relies heavily on the use of ICT. Data will be collected using light gates and
the computer can calculate the momentum before and after collision. This data is then
projected on to a screen where the students can see it, record it and manipulate it
manually. Or, if preferred, it can be exported to Excel and saved to a shared drive where
the students can access it and manipulate it in Excel.
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Overview of lesson
Lesson title: Keeping the momentum going
Approximate length of lesson: 60 minutes
Starter
Discuss what momentum is, and show a heavy object moving slowly and a
light one moving fast with the same momentum
Main
1 Collect data experimentally, collectively using data-logging apparatus
2 Manipulate the data individually and report back on findings. Teacher then
to explain the law of conservation of momentum and go through an
example
Plenary
Put examples on the board and ask students to hold up their answers on mini
whiteboards
Lesson in detail
Lesson title
Keeping the momentum going
Lesson structure
Learning
episode and
timing
Detail
Starter
(10 minutes)
Introduce the property of momentum
Using a linear air track (to remove almost all friction) and light gates,
ask a student to push a cart gently for about 1 second. Record its
final speed. Ask the same student to push another cart (now with
masses added) with the same force for the same time.
(Alternatively, this can be done by pulling back an elastic band – this
is not strictly accurate, but it will work.)
The more massive cart will have a slower speed. They may have
different speeds but they have the same momentum.
Ask questions that draw on students’ experience of moving objects
of different sizes and speeds.
Momentum = mass x velocity
Write this on the board.
Ask students a few questions regarding the momentum of different
objects ranging from electrons to elephants!
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Main 1
(20 minutes)
Start by colliding a moving cart with a stationary cart of the same
mass. (Make sure that you have the masses of all the carts written
on them.) The second cart will be between the light gates on the
linear air track. Use Blu-Tack® and a drawing pin, or magnets, to
ensure that the carts stick together after collision. Show the
momentum before and the total momentum after by using extra
columns on the spreadsheet. Students are asked to state what they
have seen.
Ask students to discuss what will happen if the stationary cart is
heavier/lighter? Then let them test their predictions, using the
demonstration kit.
Try one example where both carts are moving in the same direction
before the collision. This is hard to do as they must both pass
through the first gate and collide between the gates, but it is worth a
few attempts.
Also show one example where the carts arrive from different
directions and collide in the middle before moving off together.
Some students can use this data as an extension as it is going to
involve the vectorial nature of momentum and lead on to the work
on explosions.
Main 2
(20 minutes)
Students have to calculate the momentum before and after each of
the collisions, either manually or using Excel (if you are able to save
the data to a shared area for them to pick up).
After about 10 minutes most students conclude that the total
momentum before the event is equal to the total momentum after.
Use the spreadsheet to ensure that all of them see this. Encourage
those who are ready to think about vectors and help them to work
out the final example.
Write the principle of conservation of momentum on the board, and
make sure that all students have a record of this principle.
Explain that this principle can be used to find the velocity of vehicles
after a collision (or in accident investigations to find the speed of the
vehicles before!)
Go through a worked example on the board with input from the
students.
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Plenary
(10 minutes)
Give some simple examples and ask students to choose a final
speed from a selection. If one cart travelling at 4m/s hits another
that is stationary and they stick, what will be the final speed?
Students should write their answers on the whiteboards and hold
them up.
Also give them a variety of situations and ask them which cart has
more momentum, which is harder to stop moving? This will show
the progression from the start of the lesson. (Two carts travelling at
2.5 m/s have different masses. Cart 1 has a mass of 100kg and cart
2 has a mass of 50kg. What is the momentum of cart 1? What is the
momentum of cart 2? And which will be harder to stop? Answers on
a whiteboard please!)
Reflection and evaluation
Starter
It is useful to introduce the idea of momentum and to see that an object with high mass
and low velocity can have the same momentum as an object with low mass and high
velocity. It gives students a feel for the idea that momentum can be given to an object by
applying a force over a period of time.
Main
Main 1: During this part of the lesson the students will get a feel for the idea of
conservation of momentum. At this point it will be a general feel for the fact that, if you
increase the mass of an object, it will slow down so that its momentum stays constant.
As the session progresses, the teacher can ask various prediction-type questions to
assess if the students are getting the idea (eg ‘What do you think will happen this time?’)
Main 2: This is the point where the students will manipulate the data and come to the
more formal understanding that the total momentum before and after the collision is the
same. Personally, I tend to stick to the manual method, as you do not get distracted with
the spreadsheet.
While the students are doing this, it is useful for the teacher to mingle and guide the
students. Some students can be stretched at this point to try and explain why the final
experiment does not seem to give the correct result. If they do not get the idea for
themselves, remind them that velocity, and so momentum, is a vector.
All of this will take much less time than it has taken you to read this!
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Plenary
This is particularly useful with the mini whiteboards to allow you to see if any of the
students are confused about the principle. Some students will find the mathematical
manipulation difficult, but all should be able to answer the simple questions to do with
collision between carts of the same mass. The plenary session with the boards allows
you to see quickly how far each student has progressed during the lesson and who will
need help.
I find this fits easily in the time and allows time to develop discussion at different stages
depending on the group.
Opportunities to differentiate learning
First, all the students get a feel for momentum and understand that both mass and
velocity contribute to it. Second, it is expected that most students will be able to use the
law of conservation of momentum to find the common speed of two vehicles following a
completely inelastic collision (ie one where they stick together). Some students will be
able to cope with questions where the two objects do not stick together, or where there
is a change in direction. A change in direction brings in the whole idea of momentum
being a vector (a fact which all the students should know) and makes the calculations
more difficult.
Some students will tackle the examples with a change in direction and use the idea of
momentum being a vector. In the next lesson we will be looking at explosions and the
idea that the momentum before is zero so the momentum after must be zero and
therefore there must be positive and negative momentums.
A structured worksheet can help students who are struggling with the basic calculations
because of the mathematics involved.
Risk assessment
Not appropriate.
Opportunities to take this further
Thinking through how the principle of conservation of momentum is, in fact, consistent
with Newton’s laws of motion.
Extending the examples to think qualitatively about non-linear collisions.
Applying new understanding to road safety.
Page 8 of 9
Resources
For this lesson I use a linear air track with carts and weights that attach to them. Use
Blu-Tack® and a drawing pin, or magnets, to ensure that the carts stick together after
collision.
Each cart has an interrupter card, which interrupts a light beam in the light gates at
A and B. The signals then pass through a data logger to a computer with suitable
software installed. I find it particularly helpful to be able to display this information on my
classroom interactive whiteboard.
Mini whiteboards and board pens are issued so that I can assess quickly the
understanding of many class members. I do find that counting resources out and in is
vital!
You may also like to have calculators available for any student who has come
unprepared.
Bibliography
National Strategies Framework for Teaching Secondary Science: Overview and Learning
Objectives (2008) www.standards.dcsf.gov.uk/secondary/frameworks
Science Programme of Study for KS3 (Extract from National Curriculum) (QCA 2008)
http://curriculum.qca.org.uk/key-stages-3-and4/subjects/science/keystage3/index.aspx?return=/key-stages-3-and4/subjects/science/index.aspx
Science Programme of Study for KS4 (QCA 2008) http://curriculum.qca.org.uk/keystages-3-and-4/subjects/science/keystage4/index.aspx
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