Friday, 3 June 2011

EXPERIMENTS ~ #1 - "Sound Waves" ~ "What is Sound?"

Alisdair banging his own "drum" . . .
Ian F. Mahaney tells us, in his book "Sound Waves" that "sounds are caused by vibrations."  Mahaney outlined an experiment and Alisdair and I wanted to try it.

Mahaney says, "When an object vibrates, it moves the air around it.  You can hear and feel vibrations.  You can't see vibrations in the air, but you can see and hear things they have an effect on, like a guitar string" (Pages 20 and 21).

To do this experiment we needed:

a sheet of plastic wrap or cling film
a saucepan
an elastic band
some rice (we used an Uncle Ben's flavoured mix!)
a flat metal pan (we used a 9 x 13 cake tin)
wooden spoon

Here are Mahaney's instructions:

"STEP 1 - Pull a sheet of plastic wrap tightly over a cake pan or a large plastic bowl.  Use a large rubber band to hold the plastic in place.  You've made a drum.

STEP 2 - Sprinkle a spoonful of rice on top of the plastic.

STEP 3 - Hold a flat metal pan a little above your "drum" and tap the flat metal pan with a wooden spoon or a ruler.  When you tap the pan, the metal vibrates.  The vibrations move the air around the tray.  When these vibrations reach the plastic, the plastic vibrates, too.  When this happens, the rice moves!"

Our "drum" . . .

Drum with rice on top . . .

Our "drum" and the cake tin . . .
Alisdair says: "It was a loud experiment and I liked it better when we took the equipment outside on the lawn and it was quieter.  At first we couldn't get the rice to move.  Then Mum pulled the plastic wrap a lot tighter on top of the pan.  It worked much better after that.  You could really, truly see the grains of rice bouncing up and down, which was fun to watch!  This looked a bit like people sitting on a trampoline with just one or two people jumping!  I would definitely encourage you to try this easy experiment.  The best thing about it?  Eating the Uncle Ben's rice, once we had finished . . . I even used chopsticks!"
Alisdair enjoying eating his snack!

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