Hang on, get the binoculars, who’s that out there, not drowning but waving? Oh it’s just Jonathan Sanderson, kids science TV producer extraordinaire…

Wave Machine

Spin back to 5th May, and our Activity of the Week was a preposterous multi-Slinky monster. Anyone make that? No, thought not. Sorry about that.

This week's wave machine is just as pretty, almost as impressive, a whole lot easier to make, and even more useful in the classroom. It could also save you a packet  over buying one from the catalogues.

What you need

• A roll of gaffer tape. Duck or Elephant brands are the best. Which is a shame, since they're twice the price of the others, but so it goes.
• Lots of wooden kebab skewers.
• More fruit pastilles than seems reasonable.
• Two tables or chairs of the same height.
• a ruler, or a number of fingers that are approximately the same width as a ruler.

What you do

1. Stretch the gaffer tape between the furniture. It's probably best to try this with a 2 metre span the first time, but I've done spans of up to 4 metres with some success. You need to stretch the tape taut, which means sticking it down firmly - go right round the table or chair if you can. Mind that varnish!
2. Starting from one end, stick kebab skewers to the tape so they stick out evenly on either side. This is why you need good-quality tape - you'll need strong adhesive to hold the skewer. A damp day will ruin the adhesive, too - if your skewers fall off, this could be why.
3. Space the skewers about a ruler's-width apart. The exact spacing isn't critical, so long as they're fairly evenly-spread. Keep adding skewers until you've reached the end of the tape.
4. Now put a fruit pastille on each end of each skewer. You might think you'd only need twice as many sweets as you've used skewers, but mysteriously they tend to disappear. Further experimentation is required to ascertain precisely why. Much more experimentation. Way more, in fact.
5. However, be careful when pushing the sweets onto the skewers. Careful in case you accidentally poke your finger, but also because you want the skewer to stay balanced - it should rest horizontally. You may need to push things around a bit to make sure your wave machine stays balanced all along its length.
6. Once that's done, your wave machine is ready. Hold the skewer at one end, swiftly pulse it up and down, then let go. You should see the pulse travel the length of your tape, reflect off the far end, and return to the start. If you drive the end continuously, you can set up a standing transverse wave, too.

What's going on

Transverse wave machines like this have been around for years, but they're normally very expensive. Not only does this version cost far less, it often works better too!

The tape acts as a torsion spring, but - and this is key - one with a very low spring constant, and very low damping. The fruit pastilles and kebab skewers provide a high angular momentum, too. The result is a wave that travels down the tape at a surprisingly slow speed, as the tape struggles to return to its central position.

With a little practice, you can demonstrate not just standing waves, but things like wavepacket dispersion too. Now that's something you didn't expect to see done with a fruit pastille, right?

(the photo, by the way, is of an early prototype of this demo. It works quite well with elastic, as you see here, but the gaffer tape version is simpler, more reliable, cheaper, looks better, and is easier to set up)

Here’s writer and science teacher Ian Francis with another of those things that seemed like a good idea at the time…

Admit it- the best bits of school science lessons were getting out the old Bunsen burners, and proceeding to set fire to stuff. In this respect, you weren’t too different from chemists of olden days. Only they would explain their pyromania by a wish to investigate burning (a.k.a. combustion) scientifically. And that wasn’t mere idle curiosity, as the same stuff needed for combustion also seemed pretty handy for breathing. We know now, of course, that substances combust by combining with oxygen (a gas accounting for around a fifth of the air) but another idea held sway for over a hundred years- King Phlogiston.

This Wrong Idea from the 1600s suggested that flammable materials had a certain amount of a substance called ‘phlogiston’, and they would burn as long as supplies of it lasted. When they ran out of phlogiston, they were said to be ‘dephlogisticated’, stopped burning and left you with the calx- the ‘true form’ of the element. The idea has some sense to it- after all a bonfire stops burning after a while, leaving ashy stuff behind.

The problem was that when combustion was investigated quantitatively (by keeping track of the mass of stuff before and after), the numbers didn’t help the theory. Like the substances that gained mass on burning (and if they were losing phlogiston, surely such loss means the mass would go down?) Attempts were made to save the theory by suggesting that phlogiston was lighter than air (or even had negative weight), but the wonderful new technology which allowed scientists to weigh gasses meant that the Idea had to get the chop. Talking of which, so did Antoine Lavoisier, the chemist who in 1778 discovered oxygen. It was truly a breath of fresh air to the scientists trying to make sense of the numbers. Combustion could be explained perfectly in terms of substances joining with oxygen leaving an oxide (the ‘calx’) and so the phlogiston theory had breathed its last.

			Sing-a-long-a-ding-dong What do you get when you combine Janice ‘Knitter of the Human Gut’ Hodge, with some more silly science sing-a-longs? A bunch of her Year 6’s going crazy for these mad melodies. Have a listen to Janice’s favourite:  "What's the big attraction, it's a magnet" and the swinging Samba "E-lec-tri-city". What’s more They Must Be Giants, singers of the theme tune to Malcolm In the Middle have a song.  Janice’s daughter even wrote out the lyrics in her GCSE science. Just as well she didn’t listen to ‘You’re not the boss of me…’

			Gems Rock! Speaking of Dame Shirley and diamonds being forevAH! you’ll be wanting to know where you can find out about real gems and other precious, twinkly sparkles (round your little fingAH!) Look no further than Scotland’s Creetown Gem Rock Museum’s learning pages. They’re the ones who can tell you everything from how a crystal is formed, to cutting gemstones ready for jewellery making. If you don’t want to learn, you just want to play – there are plenty of gem-inspired online jigsaws on the site. And there aren’t any pieces missing…

			I’m sensing something here Ever wondered who was bigger – King Kong or Godzilla? Well, you’re still not really going to find out, but there’s a really funny clip on distorted perspective at the BBC website’s Senses Challenge. Have a go, see what you think…and find out what goes with white chocolate, broccoli, caviar or bacon? Eww, just the chocolate please.