John Bush: 'The lizard has been perfecting its technique for thousands of years'
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An expert in fluid dynamics from MIT was in Rio at the invitation of the Institute of Pure and Applied Mathematics (IMPA), where he participated in the Mathematics Festival.
BY ROBERTO MALTCHIK –
“I was born in Canada, the son of an Englishwoman and an American. I have been to Brazil at least once a year for the last ten years. I enjoy studying tangible things, such as the dynamics of a soccer ball and the mathematical applications in biology, even though they stem from quite complex mathematical problems.”
Tell me something I don't know.
A perfectly soft soccer ball will curve in the wrong direction. You kick it one way and it goes the other. In the past, balls had seams because it was necessary. The seams helped to give the desired curve. Now, you can even produce a super soft ball, but if you do, it will go in the wrong direction.
Why does this happen?
The roughness of a ball's surface is fundamental in determining the trajectory it will follow in the air. Anything that introduces roughness, on the scale of a millimeter, completely changes the ball's trajectory. Thus, the way the player hits it directly influences the curve it will take.
It's a shame that the player can't always calculate perfectly…
That's right. When we play with a smooth ball on the beach, we see that it goes in the wrong directions! We see the curves and we're amazed.
And how do you explain the direction of Roberto Carlos's shot?
There are two main situations: first, there's the ball with spin. When the ball is spinning, it deflects the air in the opposite direction, causing the desired curve. Now, there's the situation when the ball is flat, without spin. In this case, the air pressure changes constantly, allowing for erratic and unpredictable ball behavior. This is the effect of turbulence, considering the ball's roughness.
Why is the ball so treacherous at altitude?
Because the air density in Mexico City is 10% lower than here at sea level. Since air resistance is lower, the ball arrives sooner. Therefore, it arrives there with a smaller ball diameter than here.
It should be light enough so that you get the desired curve for the distances you expect it to travel. You could make changes, for example, to make a golf ball go further, but then you would also have to change the dimensions of the course.
You also study how some animals are able to walk on water. What's the magic?
This is related to the effect of a soccer ball, except the direction of the flow is downwards. Insects and large animals can do this. Like the lizard, which directs the flow of water downwards. It's similar to what a bird like a hummingbird does. Large animals force this flow continuously in order to support their weight. Small animals, on the other hand, can remain still on the water.
If we know how an animal stays afloat in water, would it be possible to develop a product that would allow humans to do the same?
People try to replicate it, but we would have to be stronger. And we would have to generate ten times more energy, at twice the speed, to even imagine this possibility. Even so, there is a lot of technique involved. The lizard, by striking the surface, creates a cavity and uses it to make the correct movement. You can even imagine a man walking on water, in theory, but in practice, the lizard has been perfecting its own technique for thousands of years. The fastest man with the biggest feet in the world couldn't repeat it.
*Reproduction from the newspaper O Globo
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