Datalogging in Science

Experiment to measure the speed of sound in air.

Overview

n this experiment a sound is sent down a pipe, which is closed at one end. The time interval between the sound setting off and returning to its starting point is measured, using a Sound sensor attached to a datalogger. The results are used to calculate the speed of sound. The human ear is not sufficiently sensitive to detect a time interval between the original sound and the reflected one, but the datalogger is.

Procedure
1. Assemble the apparatus as shown

2. Seal one end of the cylinder and measure its length.

3. Connect the Sound Sensor to the datalogger.

4. Connect the datalogger to the computer.

5. Open the Graph program and check the sensor configuration to ensure that it is set to record sound level in mV rather than dB. Set the sensor to record Sound level in milli-Volts
in Fast mode (e.g. for 100ms at interval of 100 micro-seconds).

6. Set a trigger value so that recording only begins when a sound above a certain threshold level is heard.

7. Begin recording

8. Make a short sharp sound (e.g. by clicking your fingers) at the point marked X in the diagram.

9. The software generates a graphical representation of the original sound and its reflection.

10. Use the Analysis features of the software to determine the time interval between the two peaks.

11. Record the time in milli-seconds.

12. Take a number of readings (by repeating steps 7 to 11) and record them in a table as shown.

13. Delete any obviously spurious ones and calculate an average for the rest.

Results:

Distance travelled by sound = twice the length of tube.

Time that Sound spent travelling = interval between successive peaks on graph

Speed of sound = Distance travelled divided by Time taken

Speed of sound = _________ (m/s)

Questions

1. Sonar is a device used for the detection and location of underwater objects. Sonar uses the same principle as was used in this experiment. What is Sonar an acronym for?

2. If the Sonar equipment used by a ship to measure the depth of the sea floor, gave a time-interval reading of 0.2 seconds, what was the depth of water under the ship (given the speed of sound in water = 1482 m/s at 20 Celsius)?

3. What would be the effect of measuring the speed of sound in a warmer room?

4. How does the speed of sound that you have measured compare to the speed of light?

5. What commonly encountered phenomenon illustrates the difference in speeds in Question 4 ?

Extensions

1. Raise the temperature of the air in the tube and measure the speed of sound.

2. Place the tube in a vertical plane, fill it with water and measure the speed of sound in water.

3. Measure the speed of sound through a solid (like wood) by placing the sound sensor on one side of your laboratory bench and making a sound travel through the bench.

Data Harvest users

1. Connect the sensor to the datalogger and the logger to the computer
2. Then click the Set Up icon to the right of this message.
3. When the software opens, click the Play button.