Category Archives: Demonstration

Understanding the chain fountain

Our chum Steve Mould has had a bit of a hit over the last few years with his chain fountain demo:

There have been arm-waving explanations (some more convincing than others), but recently John Biggins and Mark Warner in Cambridge have published a much more complete description of what’s going on.

Now, the video at the head of this post makes me wince a little, partly because I’m a snobby film-maker but also because the section from about 3:10 (about centripetal force) could, I think, be clearer. It’s not explicit, for example, that in the steady state the chain velocity must be the same all along the chain: that’s why the ‘ball being thrown straight upwards’ analogy works. It’s not that the ball is stationary at the top (if the ball’s path is arced like the chain’s, the ball isn’t stationary), it’s that the ball’s speed changes during its flight. The chain can’t do that.

There are several similar conceptual jumps which make sense only once you’ve understood the process, not whilst you’re in the process of understanding – a common mistake in academic scicomms, if I’m being snarky. You can see the result of these skipped steps in the comments thread at YouTube, which pretty much mirrors what I’d expect. That is: people tripping over precisely the parts the film covers poorly.

However, the torque argument for a force component from the beaker is lovely. The macaroni-on-a-string demo isn’t properly convincing as shown, but it does offer the beginnings of something terrific.

So, critical me thinks there’s better scicomms still to be done around this, but what delights me about the whole episode is that ‘proper’ physics is being done from a scicomms curiosity. It’s also a remainder that often science communicators stop just before the science gets properly interesting: we chicken out at the arm-waving stage rather than aiming for the greater satisfaction that comes from deeper understanding.

Bravo, Steve et al. There are precious few stories like this.

The Rutherford School Physics Partnership has a PDF of more chain problems, if you want to roll your sleeves up and get stuck in.

Ingenious, cheap way to investigate Boyle’s Law

I’ve just taught Boyle’s Law to my Year 13s and made use of the standard apparatus for demonstrating how volume changes with pressure… only I didn’t use it to do a demonstration. It was a small class, so I thought I’d try something different: I presented the class with the apparatus, told them nothing about it, and challenged them to have a play with it and a) work out what it did, then b) use it to tell me something interesting about how the world works.

The students told me later that they liked the activity because it “made them think” and they seemed to have enjoyed the process of being free to discuss ideas and work together to solve the problem I had set. I think it was a successful activity (although I suspect some students got more out of it than others), however, I wish I could have had more sets of the equipment so they could have worked in even smaller groups or even individually to explore Boyle’s Law. Next year, I might use this – a cheap, ingenious way to allow students to arrive at Boyle’s Law through experimentation:

UPDATE: Since writing this, Bob Worley has been in touch to tell me of a similar approach from CLEAPSS to allow students to explore Boyle’s Law and Charles Law with guidance available here.

If the moon were 1 pixel…

I’m not often a huge fan of computer-based demonstrations: if you’re going to show the reality of something, show it for real. However, when the thing you’re trying to show is abstract – like, for example, the immense scale of the solar system – then screen-based demos can make a lot of sense.

Take this fabulous side-scrolling solar system diagram, for example. It starts from the premise of the moon being 1 pixel high, and scales the rest of the solar system accordingly. Be warned: there’s a lot of scrolling involved.

lot of scrolling.

The journey’s kept amusing by odd little snippets spaced between the planets in neptune-sized text, and the minimal design is particularly lovely. Hey, if you’re going to use a screen-based demo, use a good one.

(via everyone, but particularly Metafilter, where the comments thread also points to the impressive-looking Universe Sandbox. “Collide galaxies for fun.”)

Not The Alom Shaha Motor

One of the great joys in my life is to come across a new science demo, particularly if it’s an elegant, simple one. I can take credit for introducing one of my favourite science communicators, Michael de Podesta, to this demo of the motor effect. Michael kindly calls it the “Alom Shaha Motor” but I can only wish that I came up with this idea myself. Jonathan and I have made a film about this, but here’s Michael’s own, elegant, simple film of the demo.

Electromagnetic induction

Thanks to one of the IOP’s twitter streams for reminding Alom and I of this film, which we’d rather forgotten about. Unlike many of our other demo videos, it wasn’t made for the IOP/National STEM Centre, nor for Get Set Demonstrate. Rather, we threw it together to enter a slightly weird competition. We held out little hope of winning, but the prize fund was considerably larger than any demo filming budget we’ve ever secured, so we had the (odd?) thought of using the winnings to fund the project we actually wanted to do.

Happily, our friends Andrew and Sharmila Hanson won, and did fabulous things with the cash, so we’re hardly complaining. (Oh, and: belated happy birthday, Andrew!).

Our EM induction film, meanwhile, ended up being loaned to the National STEM Centre so it could sit alongside the films we did make for them. The YouTube version above is still higher-quality, if you want to download it.

Funny how things turn out, sometimes. Also: I’ve just received a text from Alom complaining about how rough he looked three years ago. Tee-hee.

Eddy currents

Alom and I are filming at the moment, hence things being rather quiet around here. However, the above caught my eye. This demo is typically done with a long length of copper pipe, and the magnet takes many seconds to fall through. It’s effective on a stage.

The tall narrow pipe, however, is precisely the wrong shape to film, and on video the demo doesn’t work so well. This shorter length of fatter pipe, with an appropriate magnet, has more impact on camera.

Same principle, same demo… but different treatments for different audience contexts. So, lessons for us all:

  1. Don’t assume that the way you’ve seen a demo performed is the best way. Always look for improvements.
  2. It’s not just the demo that matters, it’s the way you use it.

That separation of ‘content’ and ‘treatment’ is, for me, an absolutely key concept.

Tip of the hat to my dad for sending this in.

Group theory and Rubik’s Cube

We can talk about maths here, right? Well hey, I guess it’s me that makes the rules, so: yes, we can talk about maths here.

You’ll have to crank up the volume, but it’s worth it: Katie Steckles‘ description of group theory and Rubik’s Cubes is as good as any I’ve seen. Better, in fact, in that for the first time in 30 years of cubing I think I understood it this time.

…and believing you understand something is the same as understanding it, yes? Oh no, wait: this site draws the line at philosophy. Drat.

Chain Reaction: Cambridge

I’m a bit of a fan of the Cambridge Science Centre, and of the people behind it. A year ago I trekked down from Newcastle to help them fix things up just before they opened. So by ‘fan’ I mean ‘groupie.’

Hence, my favourite parts of this film are Chris Lennard saying ‘Heath-Robinson‘ rather than ‘Rube Goldberg‘ (quite right too), and the brief glimpse at the end of the inimitable Dave Ansell leaning in to blow out a candle. Lovely people all.

My biggest problem with Heath Robinson machines is that they’re impossible to photograph unless they’re designed specifically for the camera. And the only people to have done that, really, are the folks behind the magnificent Japanese children’s series Pitagora Suichi, whose mechanisms are unbelievably smart:

(check this playlist for a bunch more from the same source.)