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What is the speed of sound waves?

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Nana Agyeman. 11V

What is the speed of sound waves?

Prediction: I predict that the speed of sound in air will be 330m/s.

Method: The apparatus were sat up as below.

The metal plate was held 10cm above the start microphone. It was then hit with the hammer and the time it took for the sound to travel to the stop microphone was recorded by the fast timer in microseconds. This was done twice and then the start microphone was moved to the 90cm mark on the ruler the process was repeated until the microphones were 10cm apart. However, nothing else was changed except the distance between each microphone.image00.png


Distance between the microphones (metres)

Time for Sound to travel from M1 to M2 (microseconds)













































        The graph on the previous page shows the time that was recorded for certain distances. Those distances are different from the ones stated in the results table on page 1. However this will be explained later.

        If we look at the graph we can see how the points that were plotted lie very close to the line of best fit, with the exception of the last two circled points, and show a positive correlation. Also you can see how the line goes through the origin, which should be so.

...read more.


Change in distance (m)

                        Change in time (s)

Therefore the speed I calculated, stated on the graph, was 324m/s (correct to 3 significant figures), which in actual fact is very close to the actual speed of sound waves in the air which is 330m/s.

When the plate was hit it caused the longitudinal sound waves to travel in circles until it was picked up by the first microphone. Therefore this suggests that from the middle of the circular waves (the contact point between the hammer and the metal plate) the radius must be 10cm, seeing as the plate was held 10cm above the first microphone. Now, because the waves were circular the 10cm radius must also account diagonally, where the sound wave had to pass to reach the second microphone.  

        The diagram on the next page shows what happened in diagrammatical terms of the experiment, especially when the plate was hit.


        The right angled triangle shows the points A (the contact point between hammer and the plate), B (the first microphone) and C (the second microphone). The triangle is created because after the sound waves wad travelled vertically down to B, it then had to travel diagonally to C, which for the waves is the easiest route.

...read more.


The reasons above could have accounted for the anomalies that were made.Also, however hard I hit the plate did not affect the amplitude of the sound wave and so could not have caused any anomalies.

If I were to concoct the experiment again then I would make a few changes. For example:

  • Clamp the plate down at a height of 10cm, so the distance would be reduced.
  • Use better microphones so the sound is picked up quickly and more accurately.
  • After doing the experiments I would do it again maybe 3 or 4 times, and find an overall average.
  • I would stick the ruler down to the table.

I could further this investigation in a number of ways:

  • Conduct the experiment in a bell jar to prove that sound needs a medium, like air, to travel.
  • Use different materials for the plate to see if that affects the sound through the air. It could make it travel slower or even faster.
  • Concoct the experiment in different mediums, to see if the speed of sound through the air is the same as the speed of sound through water.
  •  I could also use different distances between the microphones, and the height the plate is held at. This would allow me to plot more points and draw different graphs and work out the speed. In turn proving that sound through air is 330 m/s.

...read more.

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