Well.. you may have seen that we have been busy playing the homemade guitar over on Red Ted Art. It was lots of fun to make and the kids loved decorating it. But there was another “motif” for making the guitar – a hidden science project!
The core of the instrument is this:
A selection of different sized elastic bands – some are wider and bigger (e.g. the brown and lilac one) some are fine and really quite small (e.g. the blue one).
Put them around a container and they all produce a sound. A different sound. What is going on. And why can’t you hear it if you “twang” it between your fingers?
We had a go just holding the elastic – and you could hear something.. but not ever much. Then we put it around the box and suddenly the high pitched twang of the little blue elastic is loud and clear!
We then tried the different elastics and experimented.
1) Finger twanging versus the container – the container acts as a resonator – that means it “catches the sound” and reflects it back us. The smooth surfaces of the container ping the sound right back at us and make it sound louder.
2) The different sizes and thickness of the elastic bands. Sounds is a vibration of the air – i.e. how fast things move and the sensitive mechanisms in our pick up on these vibrations. A small elastic, pulled tight, will resonate at a much higher frequency, producing a higher sound. A big soft elastic, resonates more slowly and will make a deeper sound. So two things affect the sound – the size of the elastic and how tight you pull it.