Dr Michelle Dickinson: nanotechnologist on the new research revealing how to improve a manu

Most of the studies that have looked at how humans and animals dive into water have focused on understanding the small splash created by their water entry - think Olympic divers and hunting birds. 

New research published in the journal Interface Focus has not only done the opposite, by studying how to make the biggest splash, but has done so thanks to a fun New Zealand pastime. 

Manu jumping, a sport originated by Māori, involves leaping from bridges, wharves and diving platforms to make giant splashes. 

Each year, this is taken very seriously at the Z Manu World Champs, where the current record is a splash of more than 10m high!

An American fluid dynamitist came across a video of manu jumping on social media and ended up analysing over 50 YouTube videos of Kiwis partaking in the sport to try to understand the science behind creating the largest splash. 

Needing more data than 50 videos, he then built what he called Manubots, which were 3D printed splash-making robots. Each Manubot had a different jumper shape and were dropped into water tanks at different test angles and movements. 

The research found that the best body position for a huge splash is a 45 degree V shape when entering the water. This shape creates a perfect underwater cavity that dramatically collapses and sends water flying - which in physics is a phenomenon known as a Worthington jet. 

The angle of entry is important, but just as important is what the body does after hitting the water. Manu experts are known to do an underwater backbend and leg kick, and this motion was found to keep the air cavity open for longer before it collapses, leading to a bigger splash. 

The V shaped, kicking Manubot confirmed that the perfect splash happens when you open your body just after hitting the water. 

So, if you want to try out for the next manu champs, remember to: 

1 – aim for a 45 degree V-shape when hitting the water 

2 – Jump from the highest height possible that is still safe. 

3 – Time your underwater move so that you open your body immediately after entry. 

While this research might sound ridiculous, the study of how bodies interact with water at high speed is useful in naval design, biomechanics and even injury prevention for divers and athletes.

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Episode Transcript

Speaker 1 (00:06):
You're listening to the Sunday Session podcast with Francesca Rudgin
from News Talks B.

Speaker 2 (00:12):
Doctor Michelle Dickinson is with us with her science study
of the week. And I love the facts of the
little Kiwi tradition. A little something that's stattered on a
wallf on a summer's day inspired this particular science project.
Tell us all about it.

Speaker 3 (00:28):
So it's in the journal Interface Focus. It is open
source and I love it too. So I don't know
if you were there for the z Manu Championship.

Speaker 2 (00:36):
I think we covered it actually here.

Speaker 3 (00:38):
I love it. So it's in Auckland and it's basically
where anybody who wants to jumps off something high into
the water and there's this huge sort of like ruler
that measures how big the splash is. So, for those
who don't know, Moneu jumping is a sport originated by
Marii and it's basically where you leap from bridges whatever,
diving board wars and your whole goal is to make

(00:59):
the biggest splash ever. And we do it here because
that's what we do. But the rest of the world
thinks we're bonkers and don't actually know this exist. So
unless you're doing a cannonball. This thing doesn't really exist,
and the research really doesn't exist either, because the studies
of looking at how either humans or birds enter water
is always looking at how do they make the least
splash possible.

Speaker 2 (01:19):
You think of diving, want to be streamlined.

Speaker 3 (01:21):
You think of birds going into get they don't go, oh,
we're just going to cannonball like, so most of them
have looked at how streamlined you can be to make
the least splash. Ever, and so this fluid dynamicist in
the US came across this video on YouTube of the
Menu World Champs and was like, ohd on, what is this?
Like this is the opposite of anything I've ever looked

(01:42):
at in my life. So he started obsessively trying to
find all of the YouTube videos of Manu jumping, and
he only found fifty and so he like took all
the videos, he analyzed them. He tried to understand what
the bodies of the humans were doing to make a
bigger splash, like guessing how much they weighed, all of
those things like what are the factors? And after fifty videos,
he's like, this is not enough data. So you anyway,

(02:03):
and he built his own little he's called the menu
Bots little robots, So he three D printed these little
robots that are designed to mimic humans and basically be
propelled into water under different body shapes. So it's going, Okay,
I've looked at these videos. This is sort of the
body shape that a money jumper will do. I'm going
to make robots that do that, and then I'm going
to measure them with a high speed camera and I'm

(02:24):
going to throw them from different heights and different angles
and look at the splash that they make. If you
go to this journal into Facebocus, there are some beautiful
videos of all these little robots jumping into this little
tank of water, like it's so silly. But what he
found is that the best body position for the biggest splash.
And if you're competing next year, by the way, like

(02:45):
note this down because this is how you're going to
win the World Champs is you need a forty five
degree V shape of your body. So you need to, okay,
go in with a V shape and that creates a
little air cavity sort of by your tummy underwater, and
that air cavity eventually collapses, and when it collapses, it
sends the water flying up, and it's a physics phenomenon.

(03:08):
It's really well known. It's called the Worthington jet phenomenon.
And so he's like, oh, yeah, this is great. But
then he started to notice that the menu jumpers don't
just go in and then just PLoP in and go, oh,
I've done it. They actually do an underwater back bend
and they kick as soon as they hit the water.
And so he analyzed the physics of this and what
they're doing, whether they know it or not, is they're

(03:30):
keeping this air cavity opened for longer, allowing it a
little bit more time before it collapses, and that little
bit more time leads to a bigger splash. So if
you want to win the z Manu World Champs next year,
you need to jump off from a high as possible,
but not so high that it kills you. So there's
like a level like I think, I think here, we

(03:51):
can do it up to I don't know how many
meters it is. It was high when I watched it,
maybe five meters high. And then enter the water in
a V shape. As soon as your body enters the water,
kick back your legs do a back bend. And then
hopefully you will win, and you might be going, why
do we even care, Like why it is making the
biggest splash other than winning the champs A reason? Actually,

(04:13):
it's great Number one for studying how to have injury
prevention for divers and athletes right. And number two it's
great for interstend in biomechanics and naval design. There are
some things that you need to make a splash for
so it's great research. But I just love that this
guy came across his Kiwi phenomenon on YouTube. I was like,
what is this and now we have a thing.

Speaker 2 (04:32):
What are these people doing? I love it to thank
you so much, Michelle'll always appreciate your time.

Speaker 1 (04:37):
For more from the Sunday session with Francesca Rudken, listen
live to news Talks it'd be from nine am Sunday,
or follow the podcast on iHeartRadio