Science of Slacklining

A collaboration between QE school a partner in the Institute of Physics SPN program here  and Maverick Slacklines ( The awesomely talented Ian Jennings)

Challenging beliefs

It seems that we are very reluctant to give up our beliefs and misconceptions. Simply being presented with an alternative model rarely changes our minds. We read newspapers that reflect our beliefs and follow people on twitter we agree with. We tend to trust our intuition and have to be forced to think.

So what happens as a physics teacher when the vast majority of our students come in comfortable with their misconceptions picked up from primary school. I have huge respect for Primary Teachers they are amazing beyond belief , but very few are physicists. We are also not helped by the ‘real world’ using our very precise terminology ‘wrongly’ – forces, energy, pressure,weight and mass to name but a few, become something completely different and far more familiar than in the physicists glossary .

One way forward is to present them with something that doesn’t seem to make sense. That they cannot explain with their current model. To switch them into Kahnaman’s System 2 Thinking, to create new levels of understanding. See my blog on thinking here

It also helps if the students are engaged, can see the point and can actually feel the results of the experiment. So how might we get their interest. Put in front of them a slackline and an expert.

What is slacklining

The first stage is to get the students to understand the concept of centre of mass using a three act type approach

Which order will these cartons fall over in? One is full, one half full and the other empty empty one?

After exploring centre of mass , Ask the question whether male and females have the lower centre of mass and how you might find it. Several different methods and you may want to know what is going on here


Females have a lower centre of mass in relation to their height. A man with a strap on ‘bump’ simulating a baby is extremely unstable and prone to falling over

So the result of the centre of mass experiments

The lower your centre of mass the more stable you are (Really nice notes on animtions and centre of mass here ) and if you keep your centre of mass over the line you will remain on it.

So get on the slackline with as low a centre of mass as possible and see what happens –

Unfortunately you fall off very quickly. Now lets watch an expert. They keep their hands high and wave them around. This is surely wrong – It goes against our intuition and newly learned knowledge about centre of mass. Enter confusion – An enemy or something to be embraced?

So lets consider balancing an arrow with the mass low and then with it high. Which is easiest?

The lower the centre of mass the more stable an object is, but his doesn’t necessarily make it easier to balance. In fact it’s much harder. Why?

The reason is all down to the fact that as the further a given centre of mass is from a pivot point, the slower it will rotate and vice – versa

A classic example of this is the metronome as the mass is lowered the speed increases. This would mean that on a slackline

This is all to do with the moment of inertia. Want to know more see here

Want a slackline get one here Maverick – £55 to change your life!

One thought on “Science of Slacklining

  1. really fascinating and so well presented. Portrayed very simply in a way that makes you interact with it and throughly digest it.

    As a slackliner, I wish this was longer!

    I’m interested in why one’s center of gravity is lower on tighter lines, and then higher up in ones body on looser lines.

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