

Ping-pong gun fires balls at supersonic speeds - vinothgopi
http://www.gizmag.com/how-to-build-a-supersonic-ping-pong-gun/26082/

======
azernik
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.

~~~
ars
I find this firefox addon very useful: [https://addons.mozilla.org/en-
US/firefox/addon/nuke-anything...](https://addons.mozilla.org/en-
US/firefox/addon/nuke-anything-enhanced/)

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.)

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

~~~
maxerickson
"Remove Element" is at least similar.

~~~
pygy_
Just what I needed, thanks.

URLs for the interresed:

[https://chrome.google.com/webstore/detail/remove-
element/lnf...](https://chrome.google.com/webstore/detail/remove-
element/lnfececmldedlanmhbeljgdaofncfeho)

[https://chrome.google.com/webstore/detail/click-to-remove-
el...](https://chrome.google.com/webstore/detail/click-to-remove-
element/jcgpghgjhhahcefnfpbncdmhhddedhnk)

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ck2
The heart of the matter:

[http://www.youtube.com/watch?v=I9zBGgpzl0I&t=300](http://www.youtube.com/watch?v=I9zBGgpzl0I&t=300)

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tmh88j
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).

~~~
rtkwe
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...](http://www.gizmag.com/how-to-build-a-supersonic-ping-pong-
gun/26082/pictures#5)

~~~
tmh88j
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)

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beaker52
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.

~~~
delinka
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.

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

~~~
mdc
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.

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hakaaaaak
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>

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

~~~
rtkwe
Shattered it seems, with quite a bit of mushrooming.

[http://www.gizmag.com/how-to-build-a-supersonic-ping-pong-
gu...](http://www.gizmag.com/how-to-build-a-supersonic-ping-pong-
gun/26082/pictures#1)

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

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

