Science at key stage 3 (Year 7)
Unit 7K: Forces and their effects
Section 5: How do different materials stretch?
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Objectives |
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- to draw an appropriate curve/line graph to fit quantitative data, including choosing the scales
- why it is important to repeat measurements
- to describe and compare trends shown in graphs
- to make predictions from a graph
- to use a graph to identify anomalous data
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Activities |
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Outcomes |
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Children: |
- Ask pupils about work they did on stretching materials in key stage 2. Establish that they understand that the greater the force pulling down on a material the more it stretches. Ask pupils to explore this in more detail by adding weights to a spring, measuring the extension and predicting the extension when additional weights are added. Help them to plot a suitable graph of their results.
- One way of supporting graph plotting is to get each pupil to stand in line at a height representing the value. Two other pupils, suitably marked, represent the axes, and lie on the ground and stand to the left. (For more details see
Getting to grips with graphs (AKSIS, ASE, 1999).)
- Ask pupils to repeat the experiment with a rubber band and to plot a similar graph. Before they draw a curve through the points suggest they repeat their readings once or twice. Plot all readings and help pupils to decide what line to draw. Show examples of the graphs for both the spring and the rubber band. Ask pupils to describe the differences between them and to explain what they show about the differences in stretch.
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- represent the collected data on an appropriate line graph
- explain how they decided on their line of best fit, using repeated measurements and identifying anomalous results
- describe and compare relationships shown by the graphs,
eg with the spring, every time you add 0.1N it extends another 0.5cm, but with the rubber band the prediction is more difficult
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Points to note |
- If some pupils need additional help with graph plotting, this could be done while others take repeated readings, which could then be treated as a class set.
- The force/extension graphs for rubber bands are nonlinear at the extremes.
- With some pupils it may be better to measure length, not extension, and to compare springs of different stiffness.
- Other pupils could be encouraged to relate the stretching of materials to the idea of forces between particles. Unit 7G 'Particle model of solids, liquids and gases' includes an introduction to particle theory (not including interparticle forces).
Safety
- keep feet out of the way in case the elastic band breaks, eg by putting a large box or tin underneath so that feet are automatically clear
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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