How fast would you have to run to be able to walk on water?

Straha · Post by **Straha** » 2005-04-29 06:00pm

Don't know if this should be here or in OT, but how fast would an (average) person have to run to be able to "walk on water" so to speak?

2000AD · Post by **2000AD** » 2005-04-29 06:03pm

IIRC there's a lizardm that can do this. Anyone have any info on it?

Maraxus · Post by **Maraxus** » 2005-04-29 06:31pm

A Basalisk:
http://en.wikipedia.org/wiki/Basiliscus_basiliscus.
It claims they run 10-20 miles per hour on the water. but they only weigh about 14 ounces and have big flaps on their feet to spread out their weight.

I'd think its less the speed and more the webbing.

BlkbrryTheGreat · Post by **BlkbrryTheGreat** » 2005-04-29 07:03pm

Maraxus wrote:A Basalisk:
http://en.wikipedia.org/wiki/Basiliscus_basiliscus.
It claims they run 10-20 miles per hour on the water. but they only weigh about 14 ounces and have big flaps on their feet to spread out their weight.

I'd think its less the speed and more the webbing.

Thats exactly right- just imagine a Jet trying to skid across the water on standard landing gear.

Admiral Valdemar · Post by **Admiral Valdemar** » 2005-04-29 07:08pm

It depends a lot on mass, distribution of that mass on the surface and speed. Thos lizards are well adapted to being able to pull off such stunts, but you'd be hard pressed to get an elephant to do it even with a big boost in sprint speed.

Hardy · Post by **Hardy** » 2005-04-29 07:18pm

The foot of a 60 kg human with a surface area of 0.03 m² would likely have to hit the water at at least 6 m/s to have the water exert a force greater than that of gravity(ignoring the drag coeffcient of the human foot). I don't know how to translate that into a conclusion, however.

Straha · Post by **Straha** » 2005-04-29 07:27pm

Hardy wrote:The foot of a 60 kg human with a surface area of 0.03 m² would likely have to hit the water at at least 6 m/s to have the water exert a force greater than that of gravity(ignoring the drag coeffcient of the human foot). I don't know how to translate that into a conclusion, however.

So, about 13 miles per hour? ... Not that bad....

Captain Cyran · Post by **Captain Cyran** » 2005-04-29 07:29pm

Straha wrote:
Hardy wrote:The foot of a 60 kg human with a surface area of 0.03 m² would likely have to hit the water at at least 6 m/s to have the water exert a force greater than that of gravity(ignoring the drag coeffcient of the human foot). I don't know how to translate that into a conclusion, however.
So, about 13 miles per hour? ... Not that bad....

No, it's going to be a lot more than that. (For example, I can break 13 mph when I sprint, but no way in hell I can sprint across water) One thing you didn't take into account is the force being applied to the water when the person is bringing their leg down, which can quadruple the amount of pressure on the water easily.

Hardy · Post by **Hardy** » 2005-04-29 07:39pm

Straha, keep in mind that I did say that I didn't know how to translate it into a conclusion. It's just something to work off of.

And keep in mind that it doesn't represent the running speed; only the speed of the foot hititng the water.

Captain Cyran wrote:No, it's going to be a lot more than that. (For example, I can break 13 mph when I sprint, but no way in hell I can sprint across water)

Of course. All I calculated was the terminal velocity of a human foot in water. The force (and therefore velocity) required to gain a substantial bounce form the water (if I'm thinking correctly) is definitely much higher.

Frank Hipper · Post by **Frank Hipper** » 2005-04-29 11:38pm

Animal Planet's "Most Extreme" series had an animation of what it would take for a human to mimic a basilisk's running on water; having feet about a square meter or more in area slapping the water at machine gun pace. It were silly looking.

Patrick Degan · Post by **Patrick Degan** » 2005-04-30 12:16am

You'd have to be the Flash.

Durandal · Post by **Durandal** » 2005-04-30 01:06am

It's not just a matter of speed. It's a matter of how much water you're talking about running across and the pressure your feet exert. Regardless of how fast you're going (non-relativistically), you're going to accelerate toward the ground at 9.8 m/s^2. And if you're a human, you're going to penetrate the surface of the water.

Post by **Alyrium Denryle** » 2005-04-30 01:17am

2000AD wrote:IIRC there's a lizardm that can do this. Anyone have any info on it?

Not only the basilisk, but the chinese water dragon is also IIRC capable of doing it for short distances.

Post by **Alyrium Denryle** » 2005-04-30 01:17am

though, I admit I may be *gasp* confusing it for another "water Dragon" but it is native to South and southeast asia