Tag Archives: physics

Collapsing Can

The collapsing can demo is one I loved seeing for the first time when I was at school, although my teacher used a tin with a screwed down lid which took a little more time to cool down. In some ways I prefer the version using a can with a screw lid because the additional waiting time makes for an even more dramatic “collapse”. Doing the demo with a drink can is of course far cheaper (and I think, more reliable as it doesn’t depend on the lid being screwed down properly) and I suspect this is why the approach we use in our video has become far more widespread in schools.

I like the demo a lot but, as I hope we’ve managed to convey in the video, I think we need to be careful how and why we use it in our lessons. This is a really fantastic demo for using the Predict, Observe, Explain (POE) approach as the explanation of what’s going on is not entirely straightforward – there are a couple of things relating to the behaviour of particles and the action of forces that need to be considered and this can lead to some really interesting discussion with students, providing they’re familiar with the relevant concepts.

We’ve suggested in our video that the collapsing can demo can be used in conjunction with another demo, as a way of “scaffolding” (I really hope I’ve used that term correctly – I think this may be the first time I’ve used it in writing in this context).

Once you’ve done the demo live in class, you’ve got the perfect justification for showing your students this video of a rather more spectacular demonstration of the same physics at work:

Get Set Demonstrate logoThis film was produced for the Get Set Demonstrate project. Click through for teaching notes, and take the pledge to perform a demonstration to your students on Demo Day, 20th March 2014.

Curved space-time

I love this demo, but it’s one of those oddly bimodal ones – you can interact with it in two different ways:

  1. You throw marbles at it yourself, and stare at them. This is delightful, though rarely very informative.
  2. You’re led through a structured exploration by a demonstrator, as here. This is informative, but less delightful.

The challenge for the demonstrator is to balance their audience’s natural inclination to roll the marbles themselves with their inclination to retain control and direct attention. That is: play vs. lecture, or perhaps more appropriately here, interactive exhibit vs. demonstration.

We explore this a little in the forthcoming Demo film, which starts with a candle flame. We all love staring at the flames of an open fire, but we don’t necessarily learn very much about combustion by doing so. How we use a demonstration is perhaps more important than the demonstration itself. That’s certainly the case for teaching, and I suspect also true for storytelling.

Video found via The Kid Should See This, which also links to this useful video showing assembly.


Acoustic levitation using standing waves

Most physics teachers will have to demonstrate standing waves at some point in the school year and there are a number of standard demonstrations which can be done with school lab equipment. When teaching about them, I also show videos of standing waves I can’t recreate in the classroom and the one above is a lovely addition to my resources for this topic. This video also reminded me of a piece of art I saw at the Tate Modern several years ago – Kinetic Construction (Standing Wave) – which was the first time I saw a Physics demonstration presented as “art”.

Electric Semolina

I hope that most school children get to see that sprinkling iron filings around a bar magnet produces a pattern which shows the shape of the magnetic field around the magnet. It’s a very simple, yet useful, way of making something invisible, visible. What many school children won’t get to see is that you can do something very similar with electric fields, using semolina instead of iron filings. The picture above is from a demonstration I showed my year 13 (A-level) students last week – the instructions for how to set it up can be found at the Practical Physics site.

A tip: it’s lovely for the students to see this for themselves, but the apparatus is tiny so use a camera to project it onto your whiteboard as well. I forgot to take my webcam into school so I used my phone to take a photo and put that up on the whiteboard so we could look at the demonstration closely and discuss it. I encouraged my students to take photos too, as I did when we investigated magnetic fields – I’m not convinced getting students to draw what they see is terribly useful in this case. What do you think?

Self-siphoning beads

I really like this demo. It is simple and surprising, yet deceptively subtle and complex.

It also draws my attention to explanations. The first time I saw Steve present this he didn’t explain it, but I was transfixed. Effective demonstrations don’t always come with explanations. Sometimes less is more.

I’m no physicist, but I’m not fully satisfied by the explanation of what’s going on here. In that sense, despite the beautiful slo-mo, I preferred the first version I saw. I find this demo intensely pleasing despite it leaving me hanging.

Don’t get me wrong, I’m not advocating that we all go around deliberately producing unsatisfying explanations or consistently refusing to give any at all, but what works for me is that I’m left wanting to get my hands on a set of these to test it out, to explore and investigate the phenomenon to try to understand it better. Surely that’s one of the indicators of a great demo?

Simple accelerometer and circular motion

I’ve just started teaching circular motion to my Year 12s. There are some obvious demonstrations you can do when teaching this topic, such as spinning a bucket of water around your head, but I’m somewhat ashamed to admit that I’ve only just discovered the floating cork accelerometer which can be used to illustrate a key idea for this topic. Watch the video to see what I mean.

Massive thank you to my colleague Ronan McDonald for making the big accelerometer and volunteering to get dizzy.

[Edit 18/6/2013 – this post inspired a lively discussion at the Institute of Physics PTNC mailing list for physics teachers, which is a hidden gem of a community and a list every teacher of physics should at least be aware of. Sign up via the web interface. Thanks to everyone who cross-posted their comments here.

Joe Rowling had a nice blog post a few days before this, too – well worth a look if circular motion is your thing.


Flames and Shadows

This is a lovely demo shown to me by Andreas Tober, the Physics technician at Alleyn’s School in Dulwich, London (which also happens to be the secondary school I attended. I left shortly before Andreas started, but we’ve somehow managed to become friends anyway. Gotta love the internet). I think this is a lovely, simple way to introduce the idea of absorption spectra. I will definitely be using it in my physics teaching next year.