Measuring the speed of waves

Method 1: Measuring sound between 2 points

Measuring the speed of sound directly between two points

  1. Two people stand a distance of around 100m apart

  2. The distance between them is measured using a trundle wheel

  3. One person has two wooden blocks, which they bang together above their head

  4. The second person has a stopwatch which they start when they see the first person banging the blocks and stops when they hear the sound

  5. This is then repeated several times and an average value is taken for the time

  6. The speed of sound can then be calculated using the equation:

Speed of Sound = Distance traveled by Sound / Time taken

Method 2: Using Echoes 

Measuring the speed of sound using echoes

  1. A person about 50 m away from a wall (or cliff) using a trundle wheel to measure this distance

  2. The person claps two wooden blocks together and listen for the echo

  3. The person then starts to clap the blocks together repeatedly, in rhythm with the echoes

  4. A second person has a stopwatch and starts timing when they hear one of the claps and stops timing 20 claps later

  5. The process is then repeated and an average time calculated

Echo = 2X the distance

  1. The distance travelled by the sound between each clap and echo will be (2× 50) m,

  2. The total distance travelled by sound during the 20 claps will be (20 × 2 × 50) m  

  3. The speed of sound can be calculated from this distance and the time using the equation:

   Speed of Sound = 2 x Distance to the Wall/Time Taken

Method 3: Using an Oscilloscope 

                    Measuring the speed of sound using an oscilloscope

  1. Two microphones are connected to an oscilloscope and placed about 5m apart using a tape measure to measure the distance

  2. The oscilloscope is set up so that it triggers when the first microphone detects a sound, and the time base is adjusted so that sound arriving at both microphones can be seen on the screen

  3. Two wooden blocks are used to make a large clap next to the microphone

  4. The oscilloscope is then used to determine the time at which the clap reaches each microphone and the time difference between them

  5. This is repeated several times and an average time difference calculated

  6. The speed can then be calculated using the equation: 

Speed Of Sound = Distance Between Microphones / Time Between Peaks

Measuring Wave Speed in Water

                              Creating ripples in water

  1. Choose a calm flat water surface such as a lake or a swimming pool

  2. Two people stand a few metres apart using a tape measure to measure this distance

  3. One person counts down from three and then disturbs the water  surface (using their hand, for example) to create a ripple

  4. The second person then starts a stopwatch to time how long it takes for the ripple to get to them

  5. The experiment is then repeated 10 times and an average value for the time is calculated

  6. The average time and distance can be used to calculate the wave speed using the equation:

Average Speed = Distance Moved / Time Taken