Physics is difficult to understand from static pictures and processed texts.
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A typical picture on physics of waves for illustration purposes (Image by Loo Kang)
For example, the picture above aims to illustrate the idea of a time-dependent phenomenon such as a longitudinal wave in a closed ends pipe. The picture shows only one instant of time, say time t = T/2. However, this is not effective in developing student knowledge.
How context can aid in knowledge building
According to many educational psychologists, knowledge is constructed. Meaning is made by the human mind, rather than transmitted from notes to it. Without context, the mind has little way to situate the meaning-making process. Hence, adding the context will situate the physics described. With clear progression of lesson development, teachers can help in the bootstrapping process of knowledge building. In this case, first stating that the physics described in a situation is about the longitudinal wave of sound in a closed ends pipe, followed by showing a real-life pipe and finally progressing to a simulation will assist in knowledge construction.
The diagram shows physics at one time when it is a time-varying phenomenon
Animations can be used to depict the time-varying motion of the air particles.
Students can either use a YouTube version to explore:
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The image shows a longitudinal wave in a closed ends pipe showing regions of compression ( high air pressure) and rarefaction (low air pressure)
A gif version for repeated animation which can be inserted in electronic books or web pages.
The texts are processed or synthesized when understanding needs to be constructed
The statement "Zero displacement occurs at both the rarefaction and the compression" is a summary derived after having observed the phenomena. However, it is often presented as a fact to be summarized, which does not aid student understanding.
Text should be used to present the phenomens, perhaps at specific time like at time = 0, time = T/4, time = 2T/4, time = 3T/4 and time = T where T is the period of the wave.
A suggested text could be like this
For example, in a closed end pipe, the air particles are assumed to be ordered uniformly for ease of visualization. At time =0, the air particles are position in their undisturbed positions. The red line represents the displacement along the x-axis from the equilibrium position. Assuming period of the wave is T. At time = 0, at this point, the ends of the pipe are in the rarefaction and the middle pipe is in compression. At time = T/4, the particles are all at their equilibrium position and therefore, no regions of rarefaction nor compression. At time = T/2, the particles are distributed according to the red line, where at the ends, nodes N, the displacement is still zero away from the equilibrium. At this point, the ends of the pipe are in compression and the middle pipe is in rarefaction. At time = 3T/4, the particles are all at their equilibrium position again and therefore, no regions of rarefaction nor compression At time =T, the particles are back at the same position as T =0 and the cycle repeated.
Finally, add a simulation for students to inquiry and clarify their doubts and what if thinking. Inquiry learning is a signature learning strategy widely accepted by the Physics teaching community using both real and virtual laboratories.
You can go here for a full screen simulation!
Order of information is not intuitive
The displacement-versus-time graph should be taught before the pressure-versus-position graph as most students are more familiar with the concept of displacement after learning the topic on kinematics.
Consistently show Compression first then Rarefaction later. note that the "R" and "C" was shown probably because of the diagram positional order.
SLS Lesson
An SLS lesson has been created by the author on VLE.
You can email the author at Lawrence_WEE@moe.gov.sg ato be added to the lesson as co-editor
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