Tag Archives: physics

Imploding Can

The imploding can demo is an old classic, often done with an old square-sided oil tin though I’m personally rather partial to the Coke can version. This, however, is something else. Commentary around the web suggests the method used here is to steam-clean the tank then seal the valves while it’s still full of steam. Which sounds plausible, and it’s not ridiculous to suspect this has been done as part of an industrial safety course.

Years ago I remember talking to David Jones about trying this – he’d long fancied having a go with a petrol tanker lorry. Even for TV the costs had looked prohibitive, and I never did find him an end-of-life tanker to play with. There’s also the minor issue of disposal to consider. But at least we can now be reasonably confident we could have made it work.

One concern, though: I’m not 100% convinced by the video. It’s from an interlaced source so it’s hard to tell for sure, but frame-by-framing the implosion makes it look to me like it’s been sped up somewhat. That said, the movement of the bogies looks appropriate. Ah, YouTube, you do so tease us with your ripped-off sources and your dodgy recompression.

Pendulums [6] – Coriolis Effect

Enough of the deep-and-meaningful musings, I’m going to wrap up Pendulum Week with perhaps my favourite pendulum demo of all time. “Foucault’s!“, I hear you cry?

Well, firstly: no need to be rude. Second: actually, no. Well, sort-of no. Which is to say, yes. Ish. Only without the… er… pendulum. Look, here it is:

…and I’ll let you, dear reader, work out what to do with this one. Lovely demo.

Pendulums [5] – Not Resonance

As Pendulum Week continues here you’ll have noticed a pattern building up: that pendulums crop up in all sorts of demonstrations, but it’s often rather tricky to pin down satisfying explanations for their behaviour. Pendulums appear simple and straightforward to grasp, which is usually a good sign for demonstration tools as we want audiences to engage with ideas or behaviour and not be distracted by unfamiliar apparatus. However, I wonder if it’s possible that pendulums are too simple, in that their apparent simplicity seems to lull us into forgetting their subtleties.

Heck, unless you’re in that sin θ ≈ θ small-amplitude space you haven’t even, technically, got simple harmonic motion. Most of the time, pendulums don’t even swing like, well, pendulums. Ouch.

It feels like it ought to be possible to link pendulum demonstrations together in a neat story. A mass on the end of a string is about as simple as physics apparatus gets, surely there’s a delightful sequence of demos which can build successively, one on the other, to arrive at something complex and surprising and revealing about the world? That’s got to be possible, right?

Perhaps it is, but the origin of this series of posts lay in my noticing that pendulum demos aren’t alike, and the distinctions seem to me to be of the subtle-and-confusing kind rather than the subtle-but-illuminating kind.

Probably the best attempt I’ve seen to navigate the resulting swamp was by my colleague Marty Jopson, who made this film for the first series of Science Shack (skip to 2:40 for the start of the show):

Marty and I were co-producers on the series, and if I remember correctly he won awards for this show. I wasn’t, I should say, much involved with this episode (harrumph), but it’s still worth a watch. It gets into some of the subtleties about resonance and synchronisation that we’ve seen in this series of posts.

Pendulums [2] – Phase

After the previous post I may have got a little carried away, and we’re declaring this Pendulum Week on ScienceDemo.org. Fresh pendulum action every morning.

This beautiful demo wasn’t something I’d seen before this film appeared, though the Harvard demos folks behind it trace its history to the University of Maryland in the early 90s, and from there back to Moscow State University previously. Everything old is new again.

Anyway, it’s a beautiful demonstration of pendulum periodicity and, through that, phase. Note that the previous pendulum demo was about the efficiency of energy conversion, and hence the only real link between these two demos is the pendulum itself. You may spot a theme developing here.

Banana voltaic pile

via Twitter this morning, chemistry lecturer Mark Lorch:


Potatoes? Yes. Lemons? Absolutely. Not sure I’ve seen a banana pile before, though. Mind you, if you’re going to build a little tower of the things you might as well use acid-soaked paper anyway…

Nice twist on a familiar concept.