Waves can be longitudinal, when the particles move in the same direction as the direction of the wave, or it can be transverse, when the particles move at 90o to the direction of the wave.
Water waves are transverse waves even though transverse waves cannot travel through liquid. This is because the waves travel on top of the water.Aim:The aim of this investigation is to find out how wave speed is affected by the depth of the water.
To do this we will observe whether the depth of the water affects the wave speed of the waves in a plastic tray.Prediction:I predict that the wave speed will increase as the tray is filled up with more water. I think this because there is friction where the water touches the tray. The deeper the water the less water touches the tray and so the friction slows less water down. When there is less water more of the water will be touching the tray causing more friction and so the water will be slower. Also in previous experiments we studied refraction.
These experiments showed that when the incident waves went past the boundary between shallow and deep water at an angle they would change direction. This was because if the waves went from shallow to deep, they the part of the wave that hit the boundary between shallow and deep water at an angle first would speed up and be faster than the rest of the wave causing the wave to travel in an angle further from the normal line (90o to the boundary). If the wave went from deep to shallow, the part of the wave that hit the boundary first would become slower than the rest of the wave so the wave would bend towards the normal line.
This shows that water moves faster in deep water and slower in shallow water.Method:We will fill the 38.5cm long tray with 1cm of water. Then we will tip the tray so that one end is 5cm high then release it and this will provide the wave. The stop clock will be started from the moment the tray hits the table. We will then record the time for this wave to travel across the tray 5 times.
We chose to record the time it took to travel 5 times because the time for the wave to travel once across the tray would be too fast and it would be difficult to obtain accurate results. Also if we let the wave reflect too many times the wave amplitude would be too small to see after a few reflections and so we would not be able to measure it accurately. This will be repeated 5 times to make it easier to see anomalies and so the average results will be more accurate. We will then do the same for 2cm, 3cm, 4cm, 5cm, 6cm and 7cm of water.Fair Test – We will make sure that the experiment is a fair test by just releasing the tray and not forcing or pushing it down. We will do this because if the tray is forced down then we may give it an uneven amount of energy each time and the results will not be accurate.
Another factor that can affect the wave speed is friction. We will not change the tray during the experiment because there may be different friction on the water and so that may cause the wave to become slower if there is more friction, or faster if there is less friction. We will release the tray from the same height (5cm) each time even though the height the tray is dropped from will not change the wave speed. The height it is dropped from will change the amplitude and this is not the factor that we will be investigating.Results: ___ – anomaliesWaterDepth (m)TrayLength (m)Height ofDrop (m)Time Takenx5 (secs)Time Taken(secs)Average Time0.010.3850.055.
400.070.3850.052.170.43Results Table 2:Water Depth(m)Tray Length(m)Average TimeWave Speed(m/s)0.010.3851.
840.070.3850.420.92Analysis:The graph shows a negative correlation between the average time taken and the water depth.
It shows that the shallower the water the slower it takes for the water to travel across the tray. As the water gets deeper the time it takes to travel across the tray becomes shorter. This shows the waves in deep water travel faster and the waves in shallow water travel slower. The points are quite close to the line of best fit so the graph has a strong correlation. The first result is an anomaly and this could have been caused by an experimental error.Conclusion:I conclude that the deeper the water the faster the waves and the shallower he water the slower the waves. This conclusion fits my prediction and proves that I was correct. This is because the waves in shallow water are more affected by friction because more of the water is touching the sides and the bottom.
This slows the water down. In deep water, less water is affected by friction and this is the reason the water is able to travel faster.Evaluation:Overall the experiment worked very well and the procedure was simple, which meant there were fewer mistakes, and very effective however there were still anomalies.
Although there were anomalous results I still think the results are quite accurate because the experiment was repeated enough times to show that the results were consistent. Also the points on the graph are mostly close to the line of best fit showing a strong correlation and this means there were accurate results therefore I think the conclusion is accurate and valid.Obviously it was possible to make mistakes and errors that could affect the results and cause these anomalies. These were partly because of the equipment and partly because of human error during the experiment. One problem was that it was more difficult to count the number of times that the wave was reflected accurately when the water was deeper and the waves were faster. The stop clock may have been stopped slightly early or late and this would affect results. Also if the stop clock was started late the results would be too low or early before the tray hit the table the results would be too high and there would be anomalous results.As the water became deeper the tray became more full and this sometimes caused water to splash out of tray.
To stop this either the tray could be deeper or the experiment could be stopped earlier when there was less water. Another factor that may affect the results is if the tray was forced down instead of dropped. This may affect the results by giving the waves more energy and instead of just the gravitational energy and this would cause the waves to travel faster and the results may become too low. This is why I tried to just release the tray and not push it down during the experiment.