Chris Smith interviews Sam Reay from the Institute of Physics, London
Part of the show Science of Lasers, Light, Kung Fu and Archimedes
Sam - I'm going to attempt to break this huge block of concrete in front of me using my hand.
Chris - And this is an established kung fu move is it?
Sam - Yes, exactly.
Chris - It's quite intriguing to think that there's so much physics underlying kung fu.
Sam - Well I think there's quite a simple reason for that. Kung fu has been evolving for thousands of years, and the techniques have been improved upon by many generations of teachers. This means that people use their bodies in the most effective way to defend and attack. It's not surprising therefore that by learning kung fu you get an intuitive understanding of physics.
Chris - This piece of concrete is three inches thick, and you're going to break it with your bare hand. Why don't you talk us through the move you're going to do, and how physics is at work in breaking this bit of concrete.
Sam - The move that I'm going to use is very simple. I'm going to hit the concrete block with the bottom of the palm of my hand. Obviously if I just push down on the block, then there's no way that I'm going to break it, so I have to accelerate my hand before I hit it. I'm going to put kinetic energy into the block, and that's what's going to break it. Kinetic energy is proportional to speed squared, so if I can maximise my seed, I can maximise the amount of energy I give to the block. I need to hit the block when my hand is moving at the maximum speed. To do that, I need to aim beyond the block, because as my strike progresses, I slow down towards the end of my strike. I want to hit the block in the middle of my strike, so I aim at a point well beyond block, not at the surface itself. Another part of the technique is to put as much body mass as I can into the strike. I do this by twisting my body and lowering my torso along with my arm as I break through. So it's not just the mass of my hand and my arm that's going into the strike, it's the mass of my whole body. This is important because kinetic energy is also proportional to mass. If I can maximise the mass of the strike, then I can maximise the energy that I have to break the board. The third thing is that I have to make sure I have the maximum confidence possible. I need to believe that I'm going to break the concrete block.
Chris - So it really is all in the mind?
Sam - Well it's in the body as well, but the mind plays an important part. If I don't believe that I'm going to break this block, I will naturally slow down my hand because I'll be scared of getting hurt. Velocity is really important, so I have to believe I can do it.
Chris - Does it hurt?
Sam - It does smart quite a lot with concrete. If I break wood, it doesn't hurt that much at all.
Chris - Are you nervous?
Sam - Yeah, a little bit. It's a pretty hefty looking piece of concrete actually.
Chris - So let's see if this guy can do this, just using his hand.
(Sam breaks the block - rapturous applause)