How Does Water Depth Affect Wavespeed?
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How Does Water Depth Affect Wavespeed? Plan. In this investigation, I will be investigating how the depth of water affects the wavespeed. To do this, I will need to find out the speed of a wave in a range of water depths. So I can find the speed of the wave I will fill a tray with water. It will be a measured amount of water. Then to start a wave, I will lift one side of the tray up off the table and drop it. Here is a diagram of the equipment: When the tray hits the table, a stopwatch will be started. Then the amount of times the wavefront moves left and right between the sides of the tray will be counted. Once the wave has stopped, or we can't see it moving, the stopwatch will be stopped. Using the information I have from this I can work out the wavespeed, using the following formulae: Wavespeed = length of tray x no of times the wave went back and forth Time The equipment I will use in this investigation is: Tray, Stopwatch, Ruler, Water. To make this investigation a fair test there are a number of things I will do. Firstly, the tray will be dropped from the same height every time. This means that the wave will get the same energy from the drop every time. If it were dropped from different heights each time I took a measurement the waves would be given different amounts of energy.
There isn't a definite pattern, the speeds just increase. The possible reason for there not being a more definite pattern is experimental error. The reason that the wavespeed increases when the water depth is increased is that as the water depth increases, the friction, slowing the wavespeed, decreases. The following diagram will help to explain: In the sea or in a lake, the water depth increases as the bed becomes lower, which you can see in the diagram. There is friction between the bed and the wave. This friction slows the wave down, making the wavespeed lower. As the bed becomes lower, the friction is reduced between the bed and the wave, so the wavespeed increases. On the following page, there is a graph showing how water depth affects wavespeed. The graph does show the relationship between water depth and wavespeed and that as the water depth increases so does the wavespeed. The line of best runs through most of the points. The pattern shown by the graph is that if the water is shallow, then increasing the water depth by 1cm has a big affect on the wavespeed. For example, the average wavespeed for the water depth 1cm is 0.30m/s. If we increase the water depth by 1cm to 2cm the average wavespeed increases to 0.41m/s, which is a big increase. However, as the water depth gets deeper, the increase in wavespeed is not as big as it is in shallower water.
To make my results more reliable, I could also repeat the experiment more times. This would give even more reliable results as the more you repeat them, the more reliable they are. Also, I could make the measurement of water depth and the height of which the tray is dropped from more accurate. To do this I could work out the volume of water needed and then measured the water in a measuring cylinder. To measure the height of the tray, I could use a block of something like wood that was 5cm high. I would place it under the tray and then remove it when I was ready to start. This would ensure the tray got dropped from exactly the same height every time. Both of these improvements will make the evidence more accurate and more reliable. The evidence is sufficient to support a firm conclusion. I have plenty of evidence to support the conclusion and the evidence is mostly accurate. I can tell the evidence is generally accurate because the line of best fit on the graph runs through most of the points. To extend this investigation, I could investigate what happens with deeper water depths, to see if the wavespeed continues to increase or whether it has a maximum speed. I could investigate how changing the distance the wave has to travel affects the wavespeed. Also, I could investigate how changing the temperature of the water affects the wavespeed. These extra investigations would give me a much better conclusion, that had a lot more evidence to support it and that covered more factors that affect wavespeed.
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