Measuring the velocity of sound in air and water
The air is made up of many tiny particles. When sound is created, the air particles vibrate and collide with each other, causing the vibrations to pass between them. The vibrating particles pass the sound through to a person’s ear and vibrate the ear drum.
The velocity of sound varies with temperature and pressure, because these factors affect how the vibrations pass between particles.
The speed of sound can be calculated using the equation:
\(speed = \frac{distance}{time}\)
This is when:
- speed is measured in metres per second (m/s)
- distance is measured in metres (m)
- time is measured in seconds (s)
Example
An observer 400 m away records a 1.2 s time difference between seeing the hand signal and hearing the bang of the starting pistol.
\(speed = \frac{distance}{time}\)
\(speed = 400 \div 1.2\)
\(speed = 333 \ m/s \ (3 \ sf)\)
However, this experimental method is flawed as humans do not use stop clocks identically to one another. One person might stop the timer a fraction of a second later than another person. The values recorded will be dependent on the reaction time of the observer, and will not be entirely accurate – this explains why the answer of 333 m/s is slightly above the accepted value for the speed of sound in air.
This experiment could be improved by using two microphones connected to an oscilloscopeA device used to record signals that change regularly, such as sound or other vibrations. . By measuring the distance between the microphones and obtaining a time measurement from the oscilloscope, velocity can be calculated.