From the Global Physics Summit in Anaheim, California
The greatest pleasure of being at a huge physics conference is learning about the science of something that’s familiar, but also a little bit quirky. That’s why I always try to go to sessions given by undergraduate students, because for some reason they seem to do research projects that are the most fun.
I was not disappointed by the talk given this morning by Atharva Lele, who is at the Georgia Institute of Technology here in the US. He spoke about the physics of manu jumping, a competitive sport that originates from the Māori and Pasifika peoples of New Zealand.
The general idea will be familiar to anyone who messed around at swimming pools as a child: who can make the highest splash when they jump into the water.
Cavity creation
According to Lele, the best manu jumpers enter the water back first, creating a V-shape with their legs and upper body. The highest splashes are made when a jumper creates a deep and wide air cavity that quickly closes, driving water upwards in a jet – often to astonishing heights.
Lele and colleagues discovered that a 45° angle between the legs and torso afforded the highest splashes. This is probably because this angle results in a cavity that is both deep and wide. An analysis of videos of manu jumpers revealed that the best ones entered the water at an angle of about 46°, corroborating the teams findings. This is good news for jumpers, because there is risk of injury at higher angles (think belly flop).
Another important aspect of the study looked at what jumpers did when they entered the water – which is to roll and kick. To study the effect of this motion, the team created a “manu bot”, which unfolded as it entered the water. They found that there was an optimal opening time for making the highest splashes – it is a mere 0.26 s.
I was immediately taken back to my childhood in Canada and realized that we were doing our own version of manu from the high diving board at the local pool. The most successful technique that we discovered was to keep our bodies straight, but entering the water at an angle. This would consistently produce a narrow jet of water. I realize now that by entering the water at an angle, we must have been creating a relatively deep and wide cavity – although probably not as efficiently and manu jumpers. Maybe Lele and colleagues could do a follow-up study looking at alternative versions of manu around the world.
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