Transcript
Was Dash from the incredibles actually running fast enough to run on water, according to physics? How fast was he running anyway?
What about the Flash from the current TV show?
That’s some impressive mental math there, Dr. Definitely Not Evil, but was it accurate?
Scientists have studied this! because nerds can be awesome. Researchers back in ‘96 created a model based on the basilisk lizard, which DOES run on water.
For a human, the key parameters for the calculation are weight, foot size, step frequency, and depth each step pushes into the water. The force comes from both the initial slap against the water’s surface tension and then the foot stroke through the water.
The original researchers used a step frequency of a normal human sprinter, taking roughly 4 per second. But this is FLASH or DASH, so I removed that limit, using data from Usain Bolt and Tyson Gate as a starting point to go from step frequency to running speed.
BUT the more steps you take, the less force each one has to provide.
So, after some boring math, we get the minimum speed the foot needs to hit the water being 27 m/s, or just 60 mph, but maintaining that speed when stroking through the water would require roughly 14 times an average human’s power output.
What about for dash?
With less weight, smaller feet, and more steps to cover ground, he could be a bit slower than barry. Buut half again as fast as Usain Bolt’s record, with way more power.
And how fast was he going in the movie?
If we assume a typical security camera at 10 frames / second, and him traveling roughly 25 feet each way, he’d have to move at at least 500 feet / s to not get caught on camera. That’s 341 mph. With INSANE acceleration.
So yeah, this checks out.
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References
Humans Running in Place on Water at Simulated Reduced Gravity - 2012
A hydrodynamic model of locomotion in the Basilisk Lizard - 1996
Awesome Online Calculator (based on these 2 studies)