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Wave speed investigation

A simple investigation of wave speed with a tray half filled with water.
[Wave in a tray] This investigation is a nice, simple set up with very little instructions given to students. All you have to provide them with is a tray with some water in, a metre rule and a stopwatch. Simply, they lift the tray to create a wave. Tell them they need to calculate the speed of a wave in the tray, and that is the only instruction you provide. The equation we are hoping they will use is speed equals distance over time. They then measure the length of the tray which will give them the distance the wave has to travel.
And then they measure the time it takes to cover that distance.
This is useful to link into the forces and motion topic to show how equations from other areas of physics can be applied in other situations. The advantage of this method is students often come out with different ways of measuring the speed of the wave. Some will take repeat readings, some may time how long it takes a wave to just travel one length, whilst others may time it moving backwards and forwards and then take the average. This can lead onto a number of interesting discussions. Should they take repeat readings, should they measure the wave for just one length of the tray or let it go back and forth a number of times and then take the average?
Do students realise they need to take the average? This can help build their maths skills, and get them to see how this could improve the reliability of their results. One way to develop this further is to give groups different depths of water in their trays. This way when they record the results do they notice a difference? You can then use the change of experiment to ask “Why might this be the case?” Another way to differentiate is to see how reaction time might factor into their timings.
As you can see from the video, this is a very simple investigation that can increase in complexity depending on the level of the group you are teaching.
The equipment listed below is readily available, inexpensive and can be adjusted or adapted dependant on what you have available:
  • A Tray
  • A Metre Rule
  • A Stopwatch
  • Water
One of the aspects of this that teachers might struggle with, myself included when I first did this, is the lack of instruction you give to the students. The only instruction you generally provide is “work out the speed of the wave” which can be daunting at first. What you will find is students then discuss it in groups and perform it in a variety of different ways. This means they can evaluate which was the best method afterwards, such as did they only do one reading, repeats, what could cause errors and more. As mentioned in the video you might want the students to try different depths of water to see how this affects the speed of the wave. This is a great practical to build differentiation for learning into students’ work.
How could you use this in your classroom with your students?
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Teaching Practical Science: Physics

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