Kung Fu Science

Introduction  |  About Chris  |  About Michelle  |  What is Kung Fu  |  Breaking Blocks  |  Michelle on Physics  |  Newton's Laws  |  Conservation of Energy  |  Aspects of the Technique  |  Analysis  |  Calculations  |  The Final Test  |  Success!  |  Links and Resources

Michelle's Lab Book - Analysis

To work out the energy of my strike I enlisted the help of David James, a sports scientist from Sheffield University. Amongst other things, David designs sports equipment, so he uses high speed cameras to get finely detailed slow motion video footage of things like tennis balls and footballs bouncing. David came to the Institute of Physics to film Chris and I doing some kung fu strikes. Using specialised software I analysed the footage of me to work out the speed of my strike.

Screen-shot of Michelle's computer- showing the movement-analysis software in action. The high-speed image of Michelle is shown with position markers superimposed.

David James sets-up the Phantom, a high-speed camera capable of capturing 2000 images per second (compare this to 25 frames per second, which is the rate of frames on a normal television set)

David James sets-up the Phantom, a high-speed camera capable of capturing 2000 images per second (compare this to 25 frames per second, which is the rate of frames on a normal television set)

Chris prepares for another break as Dave gets ready to film it with the Phantom.

Chris prepares for another break as Dave gets ready to film it with the Phantom.

The high-speed footage is uploaded to a laptop

The high-speed footage is uploaded to a laptop

Using a specialised piece of software called Richimas, I analysed the high-speed footage of my strike, frame by frame. This allowed me to get accurate measurements for the speed of my hand throughout the strike

This graph shows the speed of my hand (vertical axis) plotted against the position of my hand as I perform the strike.

A graph showing the speed of Michelle's hand (vertical axis) plotted against the position of her hand as she performs the strike. The speed rises and falls, reaching its maximum, 10 metres per second, at 49% of the way through the strike.

As can be seen on the graph, the maximum speed of my strike is 10 metres per second. I've calculated that if I hit the board with this speed then the amount of energy that will go into breaking the board is 18.4 J.

This is over three times more than 5.3 J, which is the energy needed to break the wood, so I should be able to break it. The problem is that I'm putting all my faith in this so I'm still a bit scared!

Point of focus-again
The graph shows that the speed of my hand rises and falls over the duration of the strike, with my maximum velocity occurring at 49 % through the total length of the strike. This really makes sense in the light of Chris's advice about focussing on a point well beyond the actual target. If I take the target of my strike to be the board itself my maximum velocity would be reached before I got to the board, and by the time I actually hit it, I'd have started slowing down. The graph tells me that ideally I should hit the board mid-way through my swing. The high-speed footage of me practising my strike shows that I reach my maximum speed slightly too early, so I'll try to correct this when I actually do the break.

Three boards instead of one
Chris has challenged me to break though three boards, and so far all my calculations have just been for one! Thankfully, even if I need three times as much energy, I should still be ok. However, I have the advantage that the kinetic energy of the block fragments after the first break will help to break the bottom two boards for me. I hope I'm right!

Previous Section          Next Section