2 November 2011 at 20:05 #25304
This is a description of how to make a Jelly Baby Wave Machine, as demonstrated at the Surrey Physics Teach Meet on 2nd November 2011 (sorry, I don’t recall the teacher’s name!)
You will need: One roll of duct tape (the shiny silver cloth tape that is really strong, but which you can rip with your fingers) One pack of bamboo barbecue skewers, or similar, one large pack of jelly babies, four stands (with bosses, but clamps not needed) with four G-clamps or similar to hold them to the bench, two metal rods, e.g. the arms of clamps.
Unroll a few metres of tape, laying it sticky side up on a bench.
Place a metal rod at each end of the tape, with the tape wrapped around the rod. The rods will be the supports for the wave machine.
Place skewers at 5cm intervals along the tape, placed at right angles to the tape, with the tape sticking to the centre of the skewer, i.e. the same length of skewer should stick out equally either side of the tape.
Stick another layer of tape, sticky side down, on top of the first layer.
Stick a Jelly Baby onto both ends of every skewer.
Now mount each rod between two stands, held in place by a boss on either side. One pair of stands should be on the opposite side of the room to the other pair of stands, with the tape stretched between them.
If you wiggle one Jelly Baby up and down, a transverse wave will propagate along the row of Jelly Babies (and an equivalent one will pass along the other side – this can be viewed from both sides).
The wave speed can be changed by changing the tension in the tape, but it can be changed more easily and dramatically by removing the Jelly Babies. If they are removed from one half of the tape, and a wave is sent down, it will travel slowly where there are Jelly Babies, and faster where there are none.
Reflection shows the wave inverting, as it is from a fixed end.
2 November 2011 at 20:32 #25305
Just look at this video to see how the finished thing should look:
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