If you like whips and physics as much as I do, this might be the best ten…

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Cedric Lackpot -

If you like whips and physics as much as I do, this might be the best ten minutes of your day.

Found in this thread at the very lovely /r/shockwaveporn.

https://youtu.be/AnaASTBn_K4

There's a load of the usual like and subscribe bullshit at the end, but the rest is totes ossum. Enjoy.

Mike Moore - - Parent

Always nice when worlds collide!

I was a bit surprised that they'd originally thought that the fastest point was going to be at the end. My guess is that intuitively, they were thinking about acceleration (or jerk) causing the sound, even though theoretically they knew it was all about speed.

Daniel Simu - - Parent

What do you mean? The 'fastest point' does not equal 'the point that creates the sound'.

Mike Moore - - Parent

Doesn't it? Isn't it the point where it breaks the sound barrier?

Daniel Simu - - Parent

If the speed of sound is reached before the end of the strand, wouldn't you imagine the rest of the whip to keep on speeding up afterwards?
I watched back the video, and this idea of mine is can not be seen at all. Maybe the acceleration should take place but it is disturbed by the shock wave, or maybe something else is going on, I don't know much about physics to be honest. They haven't figured what happens to the tip in the last bit either (8:09 in the video)....

Mike Moore - - Parent

No, I wouldn't imagine the whip would maintain the very speed (or accelerate) into the full extension. I the tip hits its max speed after the whip has a toboggan shape and before it gets to a Chinese spoon angle (I see it as hitting its max speed close to, maybe just slightly after, a Nike smoosh).

The whip appeared to only be going over the speed of sound for a very brief period of time. Sure, its max speed and point at which it breaks the speed of sound could be slightly different, but neither appear close to the full extension of the whip.

It's only using the 3D modelling that they couldn't see what was going on at the end of the whip. The (very) high speed camera using the Schlieren method seemed to capture it well.

Mike Moore - - Parent

You got me curious and I looked up the two paper references in the video because I figured they'd have an equation for the speed. Better, they have a nice diagram. Looks like the toboggan angle is actually the winner!
https://imgur.com/a/xsT3Gxd

From the Arizona people: http://www.e-kaczor.net/keiko/whip.pdf

david - - Parent

I don’t know if the authors have or haven’t mentioned this but here is an older link to whip wave modelling
https://www.sciencedirect.com/science/article/pii/S0167278903002215

 

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