Category Archives: MrWs Maths

Measuring the speed of sound!

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!

Daniel’s fractal picture in LOGO

Daniel C was  inspired by some artwork, so he programmed this in LOGO:  http://www.j2e.com/stmarks/bwilliams/Daniel+Cs+ultimate+pattern/

download

It’s an example of a mathematical never-ending picture called a fractal.

A fractal is a never-ending pattern. Fractals are infinitely complex patterns that are self-similar across different scales. They are created by repeating a simple process over and over in an ongoing feedback loop.

I remixed it using variables here  http://www.j2e.com/stmarks/bwilliams/Remix+Daniel+Cs+ultimate+pattern/

and made it into an animated GIF

Daniels LOGO fractal

How fast does sound travel?

On Friday, a group of Year 5 and 6 children and I spent an hour outside doing some science.  Our question was “How fast does sound travel?”

We didn’t have any measuring equipment at all – we used only string, a bag of stones and a woodblock to work out the speed of sound!

Our final answer was 360 metres per second.  The actual speed of sound is 340 so we were very close considering we didn’t use any measuring tapes or stopwatches.  (We worked out we were between 5 an 10% out)

We were so busy that we forgot to take any photos – sorry!

How do you think we did it?