Tag Archives: KS4

Using Algal Balls to Investigate Photosynthesis

Video 14 May, 2014 Alom Shaha Leave a comment

As you know if you’re a regular reader of this blog, we’re big fans of using demonstrations for science teaching and have made a bunch of films about how and why to use them in the classroom. Our latest films are different – they’re about class practicals and we hope they show how these particular practicals could be used to teach specific aspects of Biology, as well as demonstrating how practicals in general might be approached to ensure their effectiveness.

The film above shows various ways to use “algal balls” in Biology practicals – they’re fun to make and a fantastic tool for doing quantitative investigations of photosynthesis. There’s more information and detailed instructions over at the SAPS website.

We’re grateful to the lovely people at Science & Plants for Schools (SAPS) for asking us to make the films – we had a blast working with them and staff from the University of Cambridge’s Faculty of Education.

Demonstration, Equipment

Not The Alom Shaha Motor

Video 28 February, 2014 Alom Shaha 1 Comment

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.

Demonstration, Performance

Magical Balancing Can

Video 23 January, 2014 Alom Shaha 9 Comments

I suspect many of you who watch the above video will know exactly how it’s done but it’s not immediately apparent to everyone, especially if you choose to present it in a way that isn’t quite honest about what’s going on.

I use this demo in my teaching to introduce the idea that an object will topple over if the line of action of its weight lies outside its base. I usually present it as a challenge: I start off with two identical (apparently) empty drink cans on my desk (yes, I know the ones in the video have slightly different designs). I offer one of the cans to a student and challenge him or her to balance it on the edge of the base. I tell them I’ll try to do the same with the other can. I make a big show of concentrating, then reveal that I have managed to make my can balance while the student’s can keeps falling over (this usually gets a gasp of approval – as I think the video shows, the can balanced on its edge looks quite disconcerting). After the initial surprise at my being able to balance the can, the students usually guess that something’s not quite right.

I think this demo works well presented as a “magic trick” because it captures students’ attention and provokes the question “what’s going on?” or “how does that work?” and that’s when the discussion begins…

UPDATE: I’ve had a couple of responses to this post on Twitter and elsewhere. I should perhaps have said that using this type of approach may not be suitable for all teachers – you have to be comfortable with the way you present a demo to a class and if showmanship isn’t your thing there’s no point forcing it (although I’d argue that this particular demo requires very little in the way of showmanship to present as a “magic” trick). We touch on this issue in our forthcoming film Demo: The Movie.

A teacher contacted me saying it was a shame I didn’t provide an explanation as it would make it easier for teachers to do the demo if they knew exactly how to do it. So, here’s the trick: place a little water in the can you want to balance before your lesson. The easiest way to judge the correct amount of water is to hold the can in the balanced position then pour water into the can until you feel it just balances. Alternatively, you could pour in liquid wax and let that set so that you have a pre-prepared can that you can keep in the equipment cupboard.

Demonstration, Get Set Demonstrate

Modelling digestion using visking tubing

Video 20 January, 2014 Alom Shaha 3 Comments

This is the second Biology film we’ve made as part of the “Get, Set, Demonstrate” project. One of the films we were asked to look at was “Making Poo: The Digestive System” but we felt that this was not what we would strictly call a “demonstration” of digestion (since no actual digestion takes place), but rather an illustration of the process. Instead, we chose to make a film about using Visking tubing to model digestion and use it to explore the reasons why you might choose to carry out a demonstration of an activity which can be (and often is) done as a class practical.

This 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.

Demonstration, Get Set Demonstrate

Collapsing Can

Video 14 January, 2014 Alom Shaha 6 Comments

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: