Working in pairs, you are going to measure the speed of sound outdoors. This sheet explains two ways of finding it; your teacher will tell you which method to use if there is not sufficient time to do both.
Equipment
Direct method
measuring wheelstopwatch measuring to
large wooden clapperhundredths of a second
This method requires an open distance of at least 300 m to get a reasonable result.
Echo method
measuring wheel
stopwatch measuring to hundredths of a second
large plane wall with 60–100 m free space in front of it.
Obtaining evidence
Direct method
1Select two points, as far apart as possible, in an open space such as a playing field.
2Use the measuring wheel to find the distance between these two points. Record this distance in column 1 of the results table.
3Repeat this measurement, record the distance in column 2 and find the mean value.
4One person goes to the first point with the clapper and the other person goes to the second point with the stopwatch.
5The person with the clapper closes it sharply, making a loud sound.
6The other person starts the stopwatch when he or she sees the clapper close, and stops it when he or she hears the sound. Record the time in column 3 of the results table.
7Repeat this twice more. Record the times in columns 4 and 5 of the results table.
8Swap roles so that the sound travels in the opposite direction and take three more readings. Record the times in columns 6, 7 and 8 of the results table.
9Calculate the mean time.
10Use speed = distance/time to work out a value for the mean speed of sound in air.
Echo method
1Stand between 60 and 100 m in front of a large plane wall. The larger the distance the better your result should be.
2Use the measuring wheel to find the distance from the wall. Record this distance in column 1 of the results table.
3Repeat this measurement, record the distance in column 2 and find the mean value.
4One person claps his or her hands so that each clap is made just as he or she hears an echo return.
5The other person uses the stopwatch to measure the time for 20 echoes.
6Record this time in column 3 of the results table.
7Repeat five times, recording the results in columns 4–8 of the results table.
8Calculate the mean time for 20 echoes.
9Calculate the mean time for one echo (echo time) by dividing the mean time found in Step 8 by 20.
10Use speed = (distance to wall and back)/(echo time) to work out a value for the speed of sound in air.
Presenting the results
Direct method
Distance in metres / Time in seconds1 / 2 / 3 / 4 / 5 / 6 / 7 / 8
Mean distance
= metres / Mean time = seconds
Mean speed of sound = (mean distance)/(mean time) = m/s
Echo method
Distance from wall in metres / Echo time for 20 claps in seconds1 / 2 / 3 / 4 / 5 / 6 / 7 / 8
Mean distance
= metres / Mean echo time for 20 claps = seconds
Mean echo time for 1 clap = seconds
Mean speed of sound = (mean distance to wall and back)/(mean echo time) =
m/s
Evaluating
What did you do to make your results more reliable?
What did you do to make your results precise?
What did you do to make your results more accurate?
The speed of sound is accepted to be between 330 and 340 m/s (it travels faster when the temperature is higher). Compare this with your result.
© Harcourt Education Ltd 2004 Catalyst 3
This worksheet may have been altered from the original on the CD-ROM.