Surface Tension, How hard is it to walk/drive on water? Options

[Lilt]

What speed does something need to go at to move over water without sinking? IIRC there is a lizard that can do it by smacking the water hard-enough with its feet that it stays afloat. I think I saw a program about iceland once where some supercharged+nitro sports buggies can do it for limited distances (10-15m?) before they slow too much as they don't have grip.

I'm just wondering what speed one would need to run at/drive at to do such a stunt. Would it be in the range of a super-adept night-one or a drek-hot sports buggy?

[Austere Emancipa...]

Driving on water with a wheeled vehicle? I'm guessing really damn fast if you want to keep it up for any length of time. A sports buggy is a light-weight 4-wheeler, right? That's certainly the best approach, and a specially shaped bottom wouldn't hurt to get a few extra meters out of it.

A snowmobile can drive on placid water for as long as there are no waves and you've got gas. I think the world record (or at least the Finnish record) was done with a standard snowmobile with 2 refuelings. With some waves, a few hundred meters should still be easy to accomplish if the starting speed is high enough.

A human being is just too heavy and has too small feet to take a step on water. If the super-adept night-one had Traceless Walk, really huge feet and weighed 30kg, [Edit]or if he was Jesus[/Edit] I'd allow it for one or two steps. Otherwise I'd just stare the player down.

This post has been edited by Austere Emancipator: Jan 27 2004, 02:03 PM

[Xirces]

Not that I'm getting obsessed or anything, but it's possible for a man to walk on custard :) but then if you were pouring enough custard powder into the water you might as well use concrete.

With a large enough support surface area I'm guessing it could be done on water, but obviously a bigger surface area will impact on speed (think big snow shoes). I think most smaller animals use the surface area trick rather than outright speed, but then the surface area probably has to increase by some ridiculous factor (3, pulling a number from my ar*e) in relation to weight for that to work.

[Spookymonster]

[Lilt]

An interesting page on the topic suggests that if you are capable of running at around 200mph then you should be meating-out the sort-of forces involved. This one suggests 65mph. So does this one. And this one has a really nifty video of the jesus lizard (Basilisk) running on water.

They all say that you'd have to expend about 15 times more energy than a human can but hey: this is SR with bioware, cyberware, and magic. Working on the slightly nicer 65mph estimate, that converts into 105km/h, which is a movement speed of 87.5m/round in shadowrun terms. Assuming you needed webbed feet (cyberfins?) for it, I'd like to see how people would go-about getting a character up-to such speeds.

I'd say take a character with 2 kid stealth legs, maxxed-out quickness mods + cyberfins (quickness 16 legs) and an Athletics(running) skill of 12 or so. That'd give an average running speed of 88m/round, although I'm sure it could be done faster using the movement power of a spirit. It's noteable that a character wouldn't be able to push against the water as he could push against the ground though so he'd probably slow-down gradually.

[Rev]

That would be a great new adept power.

However I don't think that the lizard is using surface tension to do its trick, it is just smacking the water hard and fast enough so that the equal and opposite reaction thing keeps it up.

Real surface tension walkers can stand still on the water surface, but they are all insects (eg Water Striders)

[Kagetenshi]

What do you think does the "pushing back"? The surface tension may be broken after the foot leaves the surface, but it's still surface tension.

~J

[RedmondLarry]

I think people with Wired Reflexes 3 can move like the lizard, so I've let them run short distances on water.

/Edit: I do it for the flavor, not for the physics. :)

[Austere Emancipa...]

Wired Reflexes shouldn't help you push down with your legs with significantly more energy than someone without WR. Perhaps a few percent more since you might be more efficient with your muscles (immediate feedback and correction and all that), but certainly not 15 times as much.

I suppose if someone went all the way like Lilt described, with ridiculously huge webbed feet, I would allow it at least for a sprint. I might not even hold them down to the 88m/CT speed limit, as long as they themselves and their legs were fully tricked out.

[Rev]

Read the link lilt posted for a more in depth physics explination.

[cykotek]

Just a comment on the "sports buggy" thing IRL. What you usually see doing it is Icelandic hill-climbing. These are hand-fabricated 4x4 monstrosities that usually weight under 1000 lb, and, using superchargers, nitrous and other tricks, reach excess of 1000 hp. They'll make a 10 or 15 meter sprint over standing water as part of their flat-ground running start to attempt to climb hills that start somewhere around 70 degree slopes. Rather impressive sight.

The tires they use are very equipped with large paddles molded into the rubber, and are turning so fast that they skip across the water like a stone, keeping the vehicle afloat. As long as the speed before water was fast enough, and the wheels keep turning fast enough, they'll make it across. If they bog down, they can't even make an attempt at the hill. The same principle applies to the sport of mud-bogging. I've never seen any attempts at open water crossings of any sort though. It's always standing, placid water, or artificial mud bogs.