Apr 302016

We went out onto the playground to measure the speed of sound armed with only a piece of string and a weight – here’s how we did it:

  1. We figured that speed was something to do with time and distance, so we needed a way of measuring both.
  2. Distance:
      1. Mr Williams (stood on a few whiteboards!) is 1.75m so we measured that with string 4 times making 4 x 1.75 = 7m.
      2. Then we folded the string into 7 equal lengths to make 1m.  We cut another piece of string to this 1m length.
  1. Time:

    1. Fact – a 1m long pendulum swings every 1 second.
    2. We made a 1m long pendulum using our 1m measure and tying the weight to the end.
  2. Speed of sound:
      1. Speed = distance divided by time
      2. The aim was to use a pair of claves to make a sound and bounce the sound off a wall from 50m away continuously for 100 seconds.  The sound would travel 100m between hit and echo (and by hitting in a regular beat would travel another 100 before hitting the claves again)
      3. We measured 50m by using the 7m string 7 times then the 1m once.
      4.  The pendulum kept swinging off course and hitting the goalposts to which they were tied.  Eventually we managed 38 seconds, during which we had hit the claves 59 times which worked out to be 329m/s for the speed of sound
      5. The real speed of sound is 340m/s so we were only 11m/s out – only using string to work it out!