Thursday, March 22, 2012

How fast would you have to run to "walk on water"

I attended a World Water Day recently, but this has nothing to do with conserving water or anything about food security. This is purely for light moment/s.

"Trying to walk on water, kids?"

So, how fast would you have to run to run on water? Science Focus gives us some insight:

To avoid sinking, you need to generate thrust equal to your weight. You generate this by pushing water down and backwards with each step. For a size 9 shoe, you can’t push more than around 3.5 litres of water at a time or you would sink too far and friction with the water would slow you down too much. So that 3.5Kg of water has to be pushed back fast enough to offset your weight.

If you weigh 75kg, you’ll need to push it back at around 11m/s. Since the water moves back as you push it, you need to go twice as fast as that or you would stand still. So that’s a running speed of almost 80km/hr, which would be quite impossible even in a calculation that ignores things like fluid drag.

So, if you can finish a 100m track within 10 seconds, you are running at 10m/s and you are very close, but not quite. I think Usain Bolt won't be able to accomplish that (running on water) either.

Calculation source: Science Focus

Previous article: No Plastic Bottle at World Water Day


beaty said...

lama sa inda p beach main2 oh

tehr said...

Berlari atas air?
Nak berenang pun aku tak pandai

de engineur said...

@tehr. Kena naik bot lah jawabnya. Hehe