Magical Balancing Can

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.

9 thoughts on “Magical Balancing Can”

  1. Neat stuff, I shall shamelessly steal the demo for next time I get to the moments topic… it should make a good discussion starter, and the kids are always happy when they’ve got an easily reproducible trick to take home with them!

  2. Again with the ‘magic… no, it’s science!’ approach, Alom? What, you only have one treatment for your demos?

    I jest, but there is a problem here. We often hear of people referring to science demonstrations as ‘tricks’, sometimes going so far as to present them as a magic trick before the ‘reveal’ that there’s a physical explanation. I’m rarely comfortable with this.

    Now, clearly it depends on the relationship you have with your audience, and what they take your meaning and intent to be. But in general, as a starting point, “Woo, it’s magic… no it’s not!” is, I believe, terrible advice.

  3. I love this demo, but personally I’m not keen on projecting ‘magic’ as a treatment. My reasons are several:

    A teacher knows their class. You know which ones you can ‘trick’ and they’ll enjoy it and not feel embarrassed that they’ve been tricked in front of their friends.

    The students know their teacher. They probably know that you tricking them isn’t your usual modus operandi. They know you can be trusted.

    As a performer, you know the care, attention and nuance you take in your every delivery.

    As a trainer of many presenters, it is difficult for me to know that the same care and nuance will always be delivered by every presenter in every show.

    The temptation is that ‘magic’ is seen as an easy win and performers become lazy, leaving their audience confused, tricked and with the impression that the performer is untrustworthy. Quite the opposite of what we were intending.

    Alom, I think you’ve prompted a new post from me.

  4. This demo could easily be done with the “predict, observe, explain” approach, but wearing my school teacher hat (not my science communicator one, which is a bit old and battered), I think the “magic” approach suits this demo in class, because (I hope) the ultimate response is one of delight at understanding, not embarrassment at having been duped. However, as Elin points out, this does rely on the relationship I have with the class – I hope they know that my intention is never to make them look or feel stupid. I think the classroom context is different than, say, a science show, because the demo is done in this manner specifically with the intention of having a discussion afterwards and ensuring that the students understand what’s going on – it’s not a case of “I tricked you but now I’ll explain what I did” but rather “there’s something odd going on here, what do you think it might be?” So, again, as Elin says, it’s all in the care, attention and nuance in the delivery.

  5. There is possibly a difference between presenting something as magic and showing someone something apparently impossible and challenging them to work out how it works, which has a lot of positive educational outcomes and may work better in a school than a show.

    I guess where the line is will depend on the presenter and audience.

  6. We use a “magic trick” which is also so obvious students quickly figure out how they are “tricked”, which makes it more of a joke. I have cut a wooden pole (like a broom handle but of a light wood) in half lengthwise, then hollowed it out as much as possible, fixing a rod of lead near one end. After gluing the halves together again it looks just like a broom handle. I can balance it on one hand about one quarter from the heavy end. If I place my other hand also a quarter of the length from the other end it looks just like any broom handle resting on two outstretched hands. Removing the redundant hand at the light end without the rod dropping as expected has the desired effect. For increased showmanship you can give an ordinary broom handle to a student and ask him to do exactly as you do.
    I feel these good natured tricks can hopefully put this message across: science makes us able to see through tricks and misleading claims.

  7. Alom your “predict, observe, explain” approach is a theoreticians approach. My – experimentalists – approach is the “observe, predict, observe, explain” approach. I don’t see how you can predict anything without observing.

    Personally I am uncomfortable with tricks because of the issue of trust. And there are any number of things that can inspire wonder and amazement and puzzlement without resorting to ‘tricks’.


    1. Interesting, Michael, and I dare say you’re absolutely right about O/P/O/E rather than P/O/E. However, there’s a key difference in your circumstances:

      You’re doing actual science. The P/O/E approach, on the other hand, was recommended for school situations where…

      …I think I’d better run away before I finish that sentence. Too much to do today to open that particular can of worms. 🙂

  8. I find this a fascinating discussion. Lots I could say here, but I’ll try to be uncharacteristically brief.

    Children’s magicians call these kind of treatments “do as I do” challenges. They argue endlessly whether they or the innocent volunteer should be the one who successfully completes the challenge. Both approaches *can* produce the necessary conflict to focus attention. Both *can* be pulled off without embarrassing the volunteer. They really can.

    The discussion above and elsewhere, I think, shows one thing above all else – when human interaction is involved, context is king.

    Sometimes we post here, wrongly assuming that this disclaimer is implicit in everything we discuss or suggest as a technique to consider. At least, I know I do.

    [sticks tongue in cheek] Perhaps we need a sidebar disclaimer for the blog? Like, “This is a blog about how humans communicate ideas. We publish necessarily short posts to try to stimulate discussion. If you’re looking for exhaustive context, qualifications and nuances in the posts, you’re going to be disappointed. We’re assuming that you appreciate that every suggestion in the posts depends crucially on your specific educational objectives; your character; your relationship with the audience; the expectations of the audience; the age and personality of the audience; and precisely *how* you present the activity. No technique works for all presenters, all audiences or all communication settings.”

    Might put a bit of a dampener on the comments section though 🙂

    Elin – yep, can understand your “do least harm” assessment when training new presenters. Because of the inherent risks to presenter trust and likeability, setting up volunteers to fail a challenge which you complete is an advanced technique. It’s the cliché of a terrible children’s magicians – “I can do something you can’t. Nah nah, nana, nah!” It’s the reason I fell out of love with magic as a child. I couldn’t deal with audiences and most amateur magicians thinking performing magic was really about fooling people.

    Jonathan – love to debate in more detail your general concerns about the “science magic” hook.

    Alom – for what it’s worth, I’m with you on this one. Challenge demos (with or without the magic treatment) can work very effectively in educational settings … depending on the context.

    (Yes, I know I failed on the “brief” promise – sorry.)

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