Waves and Energy

Waves and Energy

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Connecting to the Curriculum
Marking Student Responses
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This task is about looking at features of waves and making inferences based on your observations.
Facts about waves
  • Waves carry energy.
  • The waves on the surface of the ocean get their energy from wind.
  • The height and wave-length tell us about the amount of energy a wave carries.

Question 1Change answer

a)   Look carefully at this picture showing how waves change as they get close to the shore.
     Complete the sentences below.
diagram of wave behaviour at the beach
i)  As the water gets shallower the wavelength (distance between peaks) of the waves gets biggergets smallerstays the same.
ii) As the water gets shallower the amplitude (height) of the waves gets biggergets smallerstays the same.

Question 2Change answer

b)  Imagine you are swimming at a beach with waves similar to those in the picture below.
     Describe how your swimming experience would be different in the deep and shallow water.
 
More Facts About Waves
  • Waves on the sea are surface waves.
  • Surface waves occur along the boundary of two different substances, e.g., air and water.
  • In earthquakes, seismic waves can carry energy as both surface waves and waves through the earth. Surface waves cause the greatest damage.

Question Change answer

c)  Choose a boundary description for each surface wave example and place it on the table.
     The first one has been done for you.
Image counting main image

Question

d)   Compare the 2 pictures below. If the seabed in Picture A is just like the bedrock in Picture B,  what part of Picture B corresponds to the water in Picture A?
 
Waves-2-picturesx-energy-and-arrows800px-wide.png
 
 

    • The houses

    • The trees

    • The soft earth

    • The waves

Question Change answer

 In an earthquake, surface waves travel across the earth’s surface just like waves on the surface of the sea. 
 
e) i)   Look at Picture B and select the house you think will be most damaged by surface waves in an earthquake.

Question 1Change answer

ii)   Explain why you made your choice in the above question.

Question 1Change answer

f)   Using an analogy like sea waves can be useful to to predict earthquake damage, but this model may not tell the "full story". What other factors might affect which house is damaged the most?
Task administration: 
This task can be completed online with SOME auto-marking.
Level:
5
Curriculum info: 
Science, Communicating in science, Physical World
Key Competencies: 
Thinking
Keywords: 
waves, energy, earthquakes, surface waves, thinking with models
Description of task: 
Students to apply their understanding of basic wave behaviour at the sea shore to make an inference about waves in a different but analogous context: to predict where the worst damage might occur in an earthquake.
Curriculum Links: 
Key competency: Thinking
Nature of science: Communicating in science
 
Science capabilities
The capabilities focus is brought about by the conversations students have and the questions they ask.
 
Capability: Interpeting representations
This resource provides opportunities for students to discuss how scientists use a model to convey information. Comparing models for the behaviour of waves in different contexts provides an opportunity for students to strengthen their capability to make sense of representations.
Science capabilities: 
Interpret representations
Answers/responses: 
  Student responses Y10 (03/2017)
a)  i)
     ii)
Answer that includes recognising:
  • As­­ the water gets shallower the wavelength (distance between peaks) of the waves gets smaller.
  • As the water gets shallower the amplitude (height) of the waves gets bigger.
easy
 
b)
Responses should include an observation and a reason (related to the wave diagram),   
e.g., You would be tossed around more in shallower water because the waves are higher or,
If you swim out beyond the breakers into deeper water the water feels calmer because the amplitude of the waves is less.  
Don’t accept “there are more waves”. There will be the same number of waves (frequency stays the same).  As the water gets shallower the wave speed slows down. The waves bunch up so the wavelength decreases.
 moderate
c) surface waves answer with ticks.PNG easy
d)
The soft earth.
Students recognise analogous features in the 2 diagrams.
 moderate
e) i)
    ii)
House b will be most damaged.
Correct explanations involve students recognising the soft earth is effectively getting shallower (above the bedrock) and so behaves just like the waves on the beach.
  • The soft earth will behave in a similar way to the sea water when it gets shallower.
  • The surface waves will be more violent (biggest/higher amplitude) when the layer of soft earth on top of the bedrock has become very shallow, i.e., at house b.
​e.g., the earth underneath house b is the shallowest so there will be bigger waves.
An expert explanation will include a reference to energy in the wave.
e.g., The energy of the wave is most concentrated under house b as it is concentrated in less vertical depth of soft earth, and therefore this house will be most damaged.
 difficult
f)
There are a variety of other factors that could affect how much damage occurs at any point in an earthquake including:
  • what materials the houses were made of
  • how well they are built
  • how deep the quake was
  • where the quake struck and therefore the direction of the earthquake waves
  • if there were local structures that collapsed such as landslides, fallen trees, etc.
 difficult
Based on responses from 82 Year 9 and  10 students.
Diagnostic and formative information: 
   Student response Next steps
a) and
b)
Most (over 80%) of students could correctly interpret the diagram and describe the changes to wavelength and amplitude as the water became shallower.
However, less than half of the students gave a full description of what it would feel like to swim in water with waves like those represented by the model.
Common omissions or errors were:
  • Students didn't support or explain their description fully, i.e., how it would be different in deep and shallow water. e.g., It would be harder to swim in shallow water.

  • ​Some students focussed on non-science details such as the depth of the water, e.g., If I was swimming in the shallower water I would be able to touch the ground and if I was in deeper water I might drown.

  • Misinterpreting the effect of decreasing water depth on wave frequency, e.g.,  You would be hit by higher waves more frequently in shallower water whereas in deeper water the waves would be less frequent and tall.
 
When students look at the sea wave diagram, they might think there are more waves as the water gets shallower, i.e., the frequency of waves increases. It is important for them to understand that it is not possible for the frequency to change (any more than more cars can't exit a traffic bottleneck than enter it). Instead the wave speed slows down as it reaches shallower water.
Provide opportunities to view and discuss youtube or web clips showing waves on the beach etc.
d),
e), and
f)
About two-thirds of students were able to recognise that the soft earth was analagous to the sea water in the two diagrams.
However, they found it considerably more difficult to recognise how the waves in the two models behave similarly. Question e) highlighted the difficulty that students had in applying what they know about one model to a new analagous situation.
Consequently, less than half of students chose house b as the one likely to be the most damaged, and only about a fifth of students were able to correctly explain their prediction - despite the task scaffolding.
Common errors were:
  • Some students merged the two models together assuming the earthquake would bring water into the valley,  e.g., As  house c would already be somewhat submerged in water being pushed up from the earthquake meaning it wouldn't take as much damage from waves as it is not sitting on the surface, but just below it. So it would not be as badly damaged.
  • Students ignored the analogy or resorted to other aspects of prior knowledge.

    • e.g., House c, because it's closest to the direction of the surface earthquake.
    • e.g., House b, as there is a tree in front of the house, the quake energy will push the tree on top of the house. 
Question f) gave students an opportunity to draw on their prior knowledge about earthquakes to suggest other factors that could affect earthquake damage. Many students correctly suggested the materials the house was built from, or the magnitude, depth, and position of the earthquake. Students who were confused by the analogy commonly either:
  • Mentioned sea water affecting the houses, e.g., The house could get flooded or;
  • Suggested the wind could affect the earthquake waves. 
It is important for students to understand a model before they apply it to other situations.
Provide opportunities to discuss how we use models to make sense of complex ideas, and the benefits and limitations of using models.
Get students to discuss their experiences in the waves at the beach to make sense of what they are experiencing in relation to the model.
Look at other models, e.g., the water cycle, carbon cycle, and discuss science concepts behind the models and what they mean to us in terms of our day to day lives.
Next steps: 
Capability 4: Interpreting representations
Scientists represent their ideas in a variety of ways, including models, graphs, charts, diagrams and written texts.
Comparing the behaviour of waves in different contexts provides an opportunity for students to strengthen their capability to make sense of representations in the context of science
To support students to test their understanding about scientific models give them opportunities to ask each other questions about their interpretations:
  • Can they decide if the data in the model supports their explanation?
  • Is the explanation of sufficient quality to support their claim/conclusion?
  • Do they have sufficient vocabulary to give a rich an accurate description?
Students need to know quite a lot about science knowledge to be able to interpret/understand all the information a model is telling us and to be able to apply the science behind the model to alternate situations.
To support their understanding about what a model represents:
  • Can they look for what is the same and what is different when comparing two models?
  • Do they look for the relevant science?
  • Can they critique: discuss the benefits and limitations of a model?
  • Can they create their own model for a scientific idea?