Ping-pong gun fires balls at supersonic speeds | Hacker News Reader

Ping-pong gun fires balls at supersonic speeds

gizmag.com

70 pointsvinothgopi22 comments

Web Design Peeve Of The Day:

This web site pops up an overlay asking you to subscribe, which you can handily get rid of with a nice big "Close" button at the bottom. Unfortunately, on my netbook (the smallest standard size, but still a standard size) the overlay floats so that the "Close" button is just off-screen no matter where I scroll to. Don't use fixed positioning unless you've made your overlay either really small, or very adaptive to different screen sizes.

I find this firefox addon very useful: https://addons.mozilla.org/en-US/firefox/addon/nuke-anything...

I just get rid of annoyances like that using it - it's not ideal, but at least I can see the site. (Also try using the escape, some places remember to program that.)

Is there a chrome equivalent? I use the web inspector to that end, but it is slow to load.

"Remove Element" is at least similar.

Just what I needed, thanks.

URLs for the interresed:

https://chrome.google.com/webstore/detail/remove-element/lnf...

https://chrome.google.com/webstore/detail/click-to-remove-el...

I just instinctively hit the ESC key. All good :-)

Adblock. Things like that should only be a problem once.

Zoom out.

(I agree it is an annoying oversight)

The heart of the matter:

http://www.youtube.com/watch?v=I9zBGgpzl0I&t=300

I feel like the schematic is pretty worthless. I thought the picture was mislabeled because the schematic shows the chamber about the size of a two liter bottle, but the picture points towards a ~3' long tube only a few inches in diameter. That, and the nozzle is considerably thicker than the pressure chamber and the diagram shows it as being smaller. I wish I could see an actual schematic (unless they're concealing the design) because this thing is pretty cool and I really would like some details. Imagine what a racquet ball could do in this kind of design (I'm only kidding).

If you read the article you'd have found out more about the device. Specifically the tube is about 12 ft long. The actual dimensions of the pressure chamber isn't really important here it's the design of the nozzle. Which they do have a proper schematic for as it happens: http://www.gizmag.com/how-to-build-a-supersonic-ping-pong-gu...

The size and shape of the pressure chamber are important as they determine the escape velocity of the air into the nozzle, especially if it relies on a scavenging type effect (which it may judging by the vacuum line in front)

I'm amazed that the ball leaves circular hole in the bat.

I'm no supersonic ping-pong ball physics expert but I'd have expected the ball to have deformed on impact and left an irregular shaped hole and left a more destructive wake than a perfectly ping-pong ball shaped hole.

I call fake. But I'm open to being wrong.

The point is that at supersonic speeds, the ball doesn't have time to get out of the way upon impact - its literally going too fast for that, so it just keeps going .. through the bat.

Assuming a perfect sphere in a vacuum (pun? what pun?), the ball would deform perfectly by squishing in the direction of travel and expanding in all directions perpendicular to the direction of travel. The intersection of this shape with a plane is still circular.

Now, assume our perfect sphere is a ping pong ball, with a seam and variations in density along its surface. Further assume that our plane is made of wood with a variety of strengths, weaknesses and densities along its volume. And that said plane is also covered in a rough surface. The changes that these variations impart on the actual experiment leave a hole blasted in the paddle that's not perfect in anyway (see all those jagged edges?) But I believe it's safe to say that, with all these imperfections in all these materials, the circle is not a "perfectly ping-pong ball shaped hole," and certainly more difficult to measure than a perfect sphere slamming into a perfect plane.

I want to see what happens when they forget to include the ball in the experiment.

You'd get a very strong puff of air. The air leaving the end of the barrel doesn't have a lot of momentum so it diffuses pretty quickly in the ambient air. You could shape the outlet to get a more focused jet, but it's still going to be a puff, not a strong sustained stream.

The convergent-divergent nozzle reminds me a little of the design (without the kinks) of a nozzle produced by evolution strategy:

http://en.wikipedia.org/wiki/Evolution_strategy

Video of the evolution:

http://www.youtube.com/watch?v=SS2bz3xY71g

I wonder what the ball looks like after it has been fired. Flat? Intact? Or completely blown to pieces.

Shattered it seems, with quite a bit of mushrooming.

http://www.gizmag.com/how-to-build-a-supersonic-ping-pong-gu...

From the end: "do not, do not, try this at home"...e.g. "do" :)

Obituary headline: "Famed athlete, Forrest Gump dies of massive ping pong injuries"

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