About this video
Preventing cycling injury with physics.
Cycling is undoubtedly good for you but, as Donal McNally is all too aware, accidents happen.
A Professor of Bioengineering at Nottingham University his work involves simulating accidents to analyse the forces and stress acting on the human skeleton.
Cycling home in late 2010 he was involved in the "ultimate ironic accident". Hit from behind by a car he suffered a broken neck, a lower back fracture and three cracked ribs, but was saved by his cycling helmet.
As Donal himself says, this outcome was determined not by chance, but by the laws of physics.
In this short film, he explores the cycle helmet technology used to prevent injuries and fatalities on the road – including his own – and demonstrates how the extra padding around your head dissipate the energy of the impact.
In the absence of volunteers for randomised controlled trials involving real accidents, Donal performs tests using computer simulations re-running the same accident and conditions with or without different types of helmet.
Without a memory of his own near-fatal accident he can recreate the collision with a computer simulation to finally discover why he survived.
- The Royal Academy of Engineering
- Dr Donal McNally
- Nottingham, UK
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Everyone will tell you that cycling is good for you. It's a great work out. It's good for your heart and lungs, as well as your legs. Unless something like this happens. Accidents happen. And when lorries or cars are involved, they can be very serious. But the outcome is not determined by luck or fate, but by the laws of physics.
Since people aren't going to stop riding bikes or driving cars, then we need to use those laws of physics to try and prevent injuries. You want to keep something fragile, like my mobile phone safe when you post it, a good idea is to put it in a polystyrene box.
Because any kinetic energy coming from an impact gets absorbed by the polystyrene, which dissipates that energy in terms of the defamation of material, fracturing of the material, heat, and as you heard, sound. So that's exactly what cycle helmets are. They're padding for your head. They've got expanded polystyrene packaging, and they're designed to crush and reduce the energy of the impact. Now, helmets are all tested to stringent safety standards.
But the standard tests have to be simple and reproducible, and straightforward. And in helmet cases, they're basic to the point of perhaps not representing a real cycle accident. One of the standard tests for bicycle helmets is a drop from a 2 metre height onto a flat surface with a weighted head inside the helmet.
Now, we don't have a weighted head at the moment, so we'll make do with something a bit more fun. So, let's see if our cycle helmet tosses our test. I'm afraid in some accidents, the balloon doesn't survive. Just goes to show you that sometimes you have to test reality.
So the ideal way of testing the effectiveness of a helmet will be a randomised controlled trial. You take people at random and assign them to groups, either with a helmet or without, and then you make them have accidents, and you see which ones survive, and which ones don't. But that's not really ethical.
So the next best thing is to do exactly that process, but with a computer simulation. You can build the laws of physics into a computer. You can make a model of a person. You can make a models of a bicycle. You can make a model of a helmet, and then you can do that experiment.
And you can repeat exactly the same accident under exactly the same conditions with and without a helmet. If we now look at the results for what happened when a cycle helmet wasn't being worn, that's the red line. And you can see the cycle helmet has done exactly what it should do.
It's dissipated the energy, so that the acceleration peak with the helmet, the green one is much lower and broader. And in fact, only just about comes up to the 300 G limit that's set in the CPSC cycle helmet standard. If you compare that to what happened without the helmet, you can see that there's an enormous acceleration spike.
And that's the head hitting the hard ground directly, with no chance of dissipating the energy. By an ironic twist of fate, or physics, if you like, I was involved in an accident in 2010. And that was a fantastic opportunity to do some research. You have a lot of time in hospital trying to work out why you're injured the way you.
Why you've broken your neck, but your legs are fairly undamaged, that sort of thing. So once I got back to the office, it was quite fun to recreate the accident using the simulation software. And this is something fairly similar to what would have happened. This is a rear impact with the car doing 40 miles an hour. And you can see.
It's quite lucky I don't remember it. So now I have a pretty good idea of what happened to me, and I'm absolutely confident that my head helmet, in sustaining all that damage meant that I'm still alive.
So if you are involved in an accident, the best chance of saving your life is to wear a cycle helmet. And you won't catch me riding a bike without one. It's just physics.
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