Hello, and welcome to the Physics World stories
podcast.
I'm Andrew Gl, and in this episode, we're
gonna be asking the question could athletes mimic
basil lizards
and turn water running
into an Olympic sport.
It's also the title of a feature on
the Physics world website physics world dot com
written by Nicole Sharp.
The slightly surprising answer will be that yes,
shall carry Richardson,
the 100 meter world champion
could, theoretically
do it,
but would need the help of a space
agency. That's to come.
His
Nico Shaw.
I am an aerospace engineer and a science
communicator.
My training is in fluid dynamics.
So I studied the physics of fluids. I
got a Phd in that,
about,
10 years ago,
And I have long been
fascinated
with all the different ways that fluid show
up on our lives? Do you have a
blow? I do. Which we can't say... We
can't say the name of it. The name
of it is Fy d. The former name
of it, you can't say. Okay. Because it's
swearing.
Originally. Yeah. First 1, we can't say, then
it's yeah, fluid dynamic. That... That's right. That's
that was the original name. Yes. Nowadays, it's
just Fy. So what is it that makes
you squarely really excited about fluid dynamics?
You know,
it's it's funny. I went dear into an
engineering degree as an undergraduate. I I decided
probably in about
middle school. So I was maybe
12 or 13 years old when I decided
that I wanted to study Aerospace engineering.
Kind of a weird choice because I didn't
know any engineers, I
did not have any true idea what Aerospace
engineers did, but I was like, this is
what I'm gonna do.
So I go into engineering,
I'm taking all the classes, did
I'm actually simultaneously
taking
classes for a German degree. I was I
was a double major for most of my
undergraduate years.
And I'm just kinda putting up with the
engineering classes. Like, I can do them,
but they're not really all that engaging to
me, and I spend a lot more time
being interested. And in
my other classes,
until we come to a unit on fluid
dynamics,
and I remember the professor talking about how
air moved over an airplane wing
and just being
completely fascinated.
And he came to the end of 1
of the lectures he said, okay. That's as
much as we're gonna talk about this. You
have to wait to take another course from
this other. Professor, it'll be in a year
from now. And I just wanted to stand
up and shout. Don't stop now. This is
the first interesting thing. Any of you said,
So that was kind of my...
That was the moment that I think I
realized so that I love fluid dynamics.
Arguably,
I... I had been fascinated with what fluids
were doing before that because I can, you
know, think back to to various things that
I did in my childhood.
But I didn't realize that, you know, this
was a subject I could study until that
class.
And I unfortunately, did have to wait the
further year before I got to take the
class that was fully dedicated to fluid dynamics.
But,
that pretty much solidified my love for the
subject.
And I decided I wanted to do graduate
school at it.
And
I
went deep down a hole
and spent a lot of time crawling in
and out of wind tunnels.
Just wanted to do anything and everything having
to do with understanding,
particularly in my work how how error moved
around things.
But then as a a graduate student as
a Phd student. I had kind of some
downtime.
In
in my experiments when the facility that I
needed got very badly broken.
It's we're gonna have to wait for a
while for it to be available again. And
I think it was during that that I
started the blog, and I I just kinda
felt that,
here's this awesome subject that I'm constantly learning
new and interesting things about? And why doesn't
everybody else know about it and get excited
about it too? Think there's about...
3600
articles now.
Wow. I've been doing it for 14 years
Yeah. For most of that time, 5 days
a week. So that adds up to a
lot. It's it's over half a billion words.
There's presumably been quite a few areas of
fluid dynamics that have fascinated you have these
years. Can you pick out 1 that wasn't
this 1 that we're about to talk about?
Scientifically speaking,
fluids actually includes air? It includes
any gas,
liquids,
as well as things like plasma.
And in some cases,
granular materials kinda get get lumped with fluids.
So things like sand and snow and the
way that they move. So 1 thing that
I love
thinking about. And this this in some ways
touches on stuff that I studied in in
my Phd are the concept of insta instability
So a lot of times in fluid dynamics,
you'll have a situation
where
a relatively small disturbance.
Sometimes, we'll call them per renovations, are actually
able to gain energy and grow and kind
of lead from a nice orderly flow into
a very chaotic 1.
And 1 of the ones that
is
It's it's probably my favorite instability is called
the Kelvin helm halt and stability.
And it's essentially what's responsible for ocean waves.
So
when air moves over a flat water surface,
that adds the energy where if you have
any small disturbance, any ripple on the water
that makes it bigger and bigger and bigger.
And so you ultimately get ocean waves that
are, you know, curling over crest and and
breaking, you know, like, the big ones that
surfers like to ride,
So there's this absolutely
stunning thing that's happening all the time
between the air and the water.
But that's not the only place that the
Kelvin helm holds stability shows up. It it'll
show up in different layers of the atmosphere.
And sometimes you get these amazing clouds that
look like... Oh, they look exactly like Ocean
waves breaking.
And it's because you happen to have 2
layers of air that are moving pass 1
another at different speeds,
and it triggers that same.
And the thing that just utterly fa me
about this
particular 1
is
aside from the fact that it's beautiful
that you can actually see this happen,
so many different places. You see it between
the air and water, you see it between
different layers of air
to get the clouds
you also see it between different
bands of gases on Jupiter where you get
all the beautiful swirl coming together.
And I think the largest place that I've
seen it is actually in a galactic cluster.
Where we're talking, it's all of a sudden,
like, thousands of light years across,
you could get the same instability that I
can see out my window right now. Amazing.
That's amazing.
I don't want to swear about. Fluid dynamics?
Exactly. See.
I've got you. I understand it now. Okay.
So why is it?
That made you wonder whether
humans could mimic
lizards and run across water.
You know, I think the the idea originally
arose
because of watching superhero movies.
And Tv shows.
So
I remember
when the incredibles came out
that there's a a part where the little
boy who can run really fast. Dash is
able to... He surprises himself when he's running
away from the villains and he suddenly runs
across.
Cross water, and it's like, oh, cool. I
could do this.
And there was
much later
I was watching
the C w
show the flash, and I think the first
season of that. There's an episode.
Where,
Barry Allen has to run across the bay
with somebody or, like, to get to somebody
and
take care of things before there's a giant
explosion.
And his team estimate that he's gonna have
to run 650
miles an hour.
In order to run on water. And I
remember hearing that in in the episode. And,
you know, normally, as a physicist, I have
to be relatively good at you know, suspension
of disbelief when I'm watching a lot of
the kinds of shows that I like to
watch, but I I remember reading that and
being like,
that can't be right. You there's there's no
way.
Why would he need to go that fast.
And so,
I think that was part of what motivated
me to figure out, like, actually how fast
does a human have to go to be
able to run on water.
Okay. I mean, I the obvious question though
is how fast do you have to go
to run on water. Honestly only about as
fast as,
highway speed in a car. Oh okay. So,
I mean, clearly much faster than any of
us who aren't superheroes
are capable of running,
at least
assuming that you're doing it here on Earth
and that you're not, you know, adding anything
to your feet to make them bigger
or something like that.
You would only have to go about highway
speed. To be able to do it. But
it turns out there are ways that you
can get around that.
So 1 option
is that you make your feet really big.
And this is something that I didn't touch
on in the article,
but it was...
There were a couple of engineers, at Cornell
who essentially did this version of the experiment
where they they put
meter squared
they call them Lily pads, just like, I
don't know. Maybe a piece of plywood or
something across a swimming pool.
And with a little bit of practice, they
were able to run across them. And essentially
what that does is is the exact same
physics as the bass is closer and everything
that's discussed in the article.
But it basically gives you a giant foot
that you're slapping down onto the water
without having to waste the energy of pulling
it back up. It's Okay. That's kind of
fun. So they have the... These things strapped
to their feet or were they on those
left of the door? No. They they just
had them floating.
And they don't... It's not like,
there are these kind of buoyant mats that
people will run on.
On water. It's not like that because it's
not buoyant. It's it's only buoyant enough to
hold itself up. If you were to stand
still on this lily pad, you would sink.
Okay. But if you keep moving the slap,
the impulse from that slap is enough that
you can actually run across the water.
In my head when you said bigger feet.
I was thinking so clowns could do it.
So it has to be bigger than clown
feet. Right? Yeah. Yeah. At least at least
for this
version,
it would it would have to be bigger
than cloud. What what if a cloud was
running at 690
miles an hour. Would that Oh, well, that...
Then they'd have no problem. They wouldn't be
clown shoes for that.
Aside from very fast running clowns, as Nicole
mentioned, in nature some characters
are able to run on water. 1 of
them is the Basil lizard, also known for
fairly obvious reasons as the Jesus Christ there's
They're mainly found, I think in Central America
and South America, Though my understanding is that
there are pockets of them in Florida.
And they do this for relatively short distances,
and they do it primarily to get away
from predators.
Because you can imagine if something is coming
after you and you just take off across
the river.
Chances are they're not gonna be able to
come after you all that easily.
So it's a convenient
convenient skill for them.
But these lizards are about...
I wanna say a hundred grams or so.
So they're much too heavy for just surface
tension to keep them up. That's that's what
would work for, say,
a spider or a water strider or most
insects can just kind of walk across the
water because they're just way so very little.
It's not gonna work for the bass lizard.
So what the lizard does instead is it
has relatively oversized feet. And it slaps them
down hard against the water.
And just the same way that
you
having your foot hit a track causes the
track to push you back up.
That's the exact same thing that's going on
with the water, except the water is squishy
and it can move. So there's some
extra complications and trying to stay upright when
the thing that you're pushing against can move
around like that.
But generally speaking, they're getting most of their
ability to stay up from slapping the water
hard enough to give them. Vertical impulse. So
when the lizards are running, it's sort of
a circular motion in a way with their
leg. A little bit. I mean, they're they're
moving forward, they're kind of putting their foot
in, and then they pull it out before
the water closes around it. Okay.
And the
older and bigger they are, the more awkward
it looks as they do it
because they're having a harder and harder time
staying above the water. Yeah. Yeah. I can
advertise with that. Totally put something I'm finding
or playing football or cycling or anything that
the older I get, the heavier I get
the role could I look. Some reason? Yeah.
Yeah. No. I same. Alright you told me
why you're looking at it, But why are
that why are people actually looking? What's the
purpose of it? Is there any some is
there any real reason why knowing this helps
please? Well, so I can tell you that
the the biologist who has inspired to look
at this was looking at it.
In part
because she was fascinated by the similarities and
the toes
of the bass lizard which runs on water.
And a different kind of desert lizard that
runs on sand.
And so her fascination is in figuring out
how it is that these animals are able
to
run on vastly different surfaces and why it
is that there are visual similarities
between
the limbs of these
lizards doing such vastly different things.
Is that something we can learn from apart
from just knowing that these lizards have different
ways of doing things. Well, I mean, in
general, a a lot of the the kind
of work that goes on in understanding animal
lo
comes back
into play in engineering through bio mechanics and
bio robots.
1 of the things that engineers have discovered
is that it's really hard to get robots
that can move over
vastly different types of ground. Like, maybe you
can get something that works really well on
a carpet surface,
but struggles on
little no n or a tile surface or
if you spread gravel on something, all of
a sudden, it's really difficult for it to
move.
Sand is another thing that's that's really tough.
And so for a lot of engineers who
are wanting to design
robot that can get into places like
disaster zones after you've had some kind of
natural disaster. You wanna get through this rub,
find out if there's anyone there that you
need to rescue.
You need to be able to build the
devices that are capable of moving over many
different types of terrain and adapting to them.
So being able to understand how
particular
ways that, you know, how how is that
animals are able to do this and and
move so well across so many different surfaces.
Is really valuable for engineers in that respect.
But, I mean, we're not gonna be inventing
shoes to help us run across water, Are
we. That's not gonna be in.
Not on Earth.
Unfortunately, if you want to run across liquid
surfaces
on Earth.
You don't really have too many options. You
could run across Oo, which is a mixture
of corn starch and water.
It is... You can find that all over
Youtube. It is possible to run across swimming
pools of that. You do need a cement
mixer in order to mix that stuff up
at that scale.
But it is very doable.
It doesn't work quite the same way because
there's additional things going on inside the fluid.
That kind of enable you
to stay up in that
situation. If you just wanna run across plain
water,
the moon turns out to be a pretty
good place to do it.
Not that the water is there, you'd have
to, you know, take it and cope with
the lack of air and whatnot. But the
gravity on the moon is actually about right,
so that people are capable of keeping themselves
up on the water that's...
That was actually shown in an Italian experiment
that I did discuss in the article,
were they essentially
put people in a harness
that mimics being at lunar gravity
or or other reduced gravity
situations, and they had them run in place
with fins on their feet that made them
have
proportionately sized
feet like a basil. So a little bigger
than human feet kinda like your clown shoes.
And they would just run in place over
this pool that they were suspended over, and
you can see in the footage, which is
absolutely amazing to watch.
That
it is possible
for
a human to support themselves at least for
several seconds at a time. I think
at lunar gravity,
everyone that they had that they were testing
could do it.
But as they increased the gravitational
the equivalent grab gravity levels, it got harder
and harder for people. Just going back to
watching Apollo astronauts.
Wish I've done a lot. Oh... There a
lot of fun. Absolutely. But they don't do
a lot of running. They do a lot
of bouncing. Is it is it possible to
run on the moon. I think it would
probably take some practice to figure out exactly
how to do it. It's fair to say
that the... There... It's unlikely that your stride
is going to look the exact same. That
if we're gonna make an Olympic sport out
of this, which I... It's the ideal thing.
Right? We we're not going to go to
the moment to do that.
Can you see an Olympic sport in the
swimming pool with these lily pads on it?
And I mean, they could.
If if they did the Lily pad option,
that that is feasible.
And it that would be
really interesting
to see people raising. I think they would
have to do it in kind of time
trial sort of way because if you had
multiple people jumping for the same lily pad
at once, everyone's just gonna fall.
Apparently, you have to hit the middle of
the Lilly pad quite well to get it
to work. Otherwise, you lose your balance and
you fall off. This sounds pretty skill, which
is what you want from middle olympics. Yeah.
Say what worries mean about it though the...
Is the end? How do you stop? I
think you have to transition from... Just like
the lizard do. Right? You transition from being
on the water to being on
the side of the pool. Yeah. Actually... That's
how the lizards do it. They run from,
like, ground
across the water and back to ground.
As opposed to the g who being water
birds, they're happy to do it just
from the water to the water. So g
are pretty spectacular
because they're about 10 times heavier than
the
lizards.
I think they they are, like, 2 2
and a half kilograms
these birds.
They're black and white. They don't look all
that
spectacular.
They just, you know, look like water birds.
Except they have this
behavior that they do when they're mating, they
have a display called Rushing,
where
the 2
mated graves
will
rise up out of the water, kicking their
feet
as fast as you can
you know,
imagine practically.
I think it's about 20 steps a second.
It's ridiculous compared to anything that you know,
a human can do.
And when they do this, they rise up
out of the water with their wing stationary
behind them. So they're not getting any help
from their wings at all,
and they just run across the water for
20 meters or so.
It's like a synchronized swimming display except running
on water. Yeah. It's amazing. Quite apart from
the running and water bit, the whole display
is an incredible. An incredible thing. Oh, yes.
But is that sort of effectively the same
as the lizards? The way they're doing. Yeah.
The physics The physics is very much the
same.
The 1
significant difference I would note between them is
that the birds... Pull their feet out of
the water differently.
And it's a little unclear exactly what goes
on during that step because it happens underwater,
and you can't get g to do this
in the lab. You can only do it
when you're out in the field. So it's
really hard to see what's happening under the
water from
cameras that are second on land. Massive boats
float on water. The way that that boats
and people float on water is with buoyancy.
So it it relies on us
displacing a volume of water
that
is,
well,
it equal to the
weight
that we have
under the water essentially. So the further submerged
you are, and the more you can push
water aside, the more of a buoyant force
you get.
That doesn't really help with the basil
and the g because not very much of
them is underwater. If they were would that
help? I mean, like, could you sort of
run just underneath?
I mean at that point you're just swimming.
That's it's like the duck. Right? The their
feet are going wild underneath the surface, but
they look like they're just lighting along other
there Olympia who are competing in Paris who
could
effectively run on water. Yes.
There are Olympia in Paris who have the
speed that they could run on water,
not on earth.
We would we would have to be having
the space Olympics.
1 option as as I said before is
we could...
Have events on the moon and, you know,
just transplant a pool up there.
Another option, which I think is is a
particularly
interesting 1 is having
instead of water running, having ethane running
across the lakes of Titan. That sounds amazing.
Titan is 1 of Saturn's moons.
It's a particularly
interesting place because it's the only other place
in our solar system that has surface level
liquid
bodies place so lakes and seas, and oceans.
Prior to to finding out that Titan has
these
hydrocarbon lakes.
We thought that Earth was the only place
that that just had liquid sitting on the
surface that you could swim or run in,
Why would we be able to run on
that un titan? Mostly because titan is smaller
than Earth, it has, less gravity.
Which means that, in general, you don't have
to have as much vertical impulse, or you
don't have to be creating the same amount
of force to keep yourself up just because
your lighter.
But also because of the ethane rather than
water. Yeah. There's
funny thing about it is that, the density
of
the ethane is lower, So it actually doesn't
help you as much as water. Like, if
you could have water there, that would that
would make it a little bit easier,
but that's not what they have. They have
ethane thing. Oh, okay. So would actually be
more helpful if it was water. Little bit
more helpful, You would get a little bit
more vertical out of it. If they had
water, we'd already be there though. Right? Yeah.
Well, if
what water does exist on titan is frozen
because it's extremely cold there.
Okay. Okay. So you're gonna have to run
in jumpers. Yeah. Yeah. You're you're gonna have
to be able to dress very warm and
hold your breath. Okay. Yeah. Diaz is not
gonna be great. Is it on tight? No.
Okay. As colleague explains in the feature on
physics well dot com, it's not just anybody
who could run across the likes of Titan.
1 person who could is the Us sprinter,
Shi carry Richardson.
The fastest woman in the world right now.
Running on titan legs, racism and have the
advantage of weighing just 45 kilograms,
while her Uk size 5 shoes provide a
good foot area.
According to Nicole calculations, the Us athlete fleet
would have to run at about 8.7
meters per second.
That's within her world championship time, which she
ran at 9.3
meters per second. For those of us who
are, slightly larger and not quite so blistering
fast as Richardson.
We could, of course just enter the Titan
freestyle swim instead.
You first.
Back to Nicole now, and my 1 last
question for her, which is
are we really gonna be adding this to
the Olympics.
Well, I think, you know, it it might
be an idea a little before its time
still,
we're gonna have to get get
creative
to to bring it into the Olympics. And
I imagine the Io is going to have
a lot of questions shenzhen. While we might
have to wait some time for the space
olympics pixel running on water to be part
of the Olympic games. This year's Olympic games
in Paris run from the 20 sixth of
July to the eleventh of August. And 1
news sport that you can find in there
is breaking or break dancing. And if you
want to know about the physics of that
and plenty of other sports, sport You can
go back to our previous episode of the
Physics World stories podcast where we hear from
John Eric Go. The author, of gold medal
physics, the science of sports
And of course, you can find out much
more about the potential and the nature of
running on water
in the coal shops article on physics world
dot com could athletes,
mimic basil lizards and turn water running into
an Olympic sport.
Next month we'll be delving into some of
the drama in the recent past
of so.
The hump for the Higgs boson on that
Lhc switch on, and
well, how did they end up not destroying
the world?
And how could they capture
the public's
imagination again?
That's next month, but for now,
Enjoy the Olympics, and thank you very much
for listening.