# Video: Shattering a CD at 170,000FPS

â€śin which they spin a compact disc at 23,000RPMâ€ť

They say 80,000RPM at 48s. I wonder which it is - did they not reach their target?

23,000 rpm? Thatâ€™s a record-breaking speed!

Or, CD, I guess.

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â€śWeâ€™re going to spin a CD literally at warp-speedâ€¦â€ť [emphasis added]

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I was bored so some nerdery:

A 1x CD spins at 500 rpm max, and reads data at 150 KiB/s

So if it were possible to read the CD at the speeds of this video, itâ€™d be a 4600x speed drive at 690000 KiB/s (706.56MB/s) Itâ€™d also read the entire disc in less than a second.
If it were a DVD, itâ€™d be 6934MB/s
If it were a Blu-ray, itâ€™d be at 20700MB/s

Assuming my dodgy maths is correct of course
edit: got a decimal point wrong, now fixed i hope

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He said the Dyson motor could achieve 80000 rpmâ€¦

New Dysons can achieve 120000 rpm so yeah!!!

I thinkâ€¦ Yup a quick google confirms it ish that a CDs designed rpm limit is approx 23000 rpmâ€¦hence the 23000 quoteâ€¦ and the vid is shot at 28000 fps

You people need to watch shit a bit more before piling onâ€¦

And OK he exaggerated about Warp speed but the discs did warp at those speeds

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Wellâ€¦ Iâ€™d say that the z-axis deformation counts as a sort of warping. (Oops, gothicgeek beat me to it.)

Itâ€™s fascinating to see these phenomenons in slo-mo.

That said, they need some hardware for automatic or at least remote stopping of the cameras, the manual shutdown is a potential failure point.

A â€śstop the camerasâ€ť button via some sort of wired (or perhaps even wireless if the rf weather in the area is favorable) link would do the job.

If it would be extra-hightech, the stop signal could be triggered with some sort of a sensor, with an optional programmable delay. In this case Iâ€™d use a reflectance sensor deteting the presence of the CD optically. (Caveat: test performance in the bright light the fast cams need.) CD vanishes - wait 100 milliseconds and then stop the cameras and the motor.

With various kinds of sensors, many such experiments could get semiautomated, making the data acquisition way easier and more reliable and repeatable.

Also, a stencil for painting a grid or array of dots or anything else for later computer-vision analysis of the deformations would be a nice touch. Laser-cut, and then spray-on or manually draw with a pen, with taking care of not adding too much mass and not damaging the surface (both, if too significant, would interfere with the measurements).

An optical rpm sensor would also be nice. If it is made with directly driven (non-multiplexed) segments, it could provide data without flickering even to the high-speed cam. Optionally, some sort of sync signal (even a single blinky LED would do) and a separately recorded data stream.

(I love icingâ€¦)

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The meme with guy raising his finger and walking off is meant to indicate I was about to be excessively pedantic, but then realized that it was actually a correct use of the word.

Black background, Iâ€™m sure it would work.

Also, am I the only one who was pleased to see people wearing lab coats that are more than just props?

Ahhhh! (I have to admit I am not 100% well-versed with the memes out there. Was not certain if it is the first or the second guy who is leaving.)

Or a 100 kHz (or reasonably higher, until we run into cutoff of reasonably cheap parts) reflectance beam and look only for the AC component. We donâ€™t need a microsecond-fast reaction, a millisecond is by far enough. (I thought about sensing from the back side of the CD, so we wouldnâ€™t have any gear over the front face where it could be seen or interfere with things.

Was a nice touch!

Though in this specific test Iâ€™d go rather for a thick leather apron and a full-face shield in addition to the goggles. The shrapnels can ricochet. On the other hand, some say that scars are sexyâ€¦

And here I just watched the season 1 Mythbusters episode where they did just this.
What timing.

Seeing exactly how it fractured and broke apart was a nice addition.

That said, this was careless. Even if they couldnâ€™t get the kind of polycarbonate the Mythbusters used they should have put up some sort of shield in front of them.

That Mythbusters episode already showed that doing this can embed large fragments inches into flesh (testing with ballistics gel of course).

If that audio was real, it must have some incredibly fast a/d converters and mics sensitive to really high freqs. I wonder how they avoid shoot noise at that frame rate.

Meh. This is the real slo mo guy. Filming at 1 trillion fps.

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Is everything these guys own completely trashed? I mean, look at their lab coats, look at the one guyâ€™s bruised purple fingernail, and what the hell happened to that tree theyâ€™re hiding behind? Keebler Elf Ninja Woodsmen?

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Itâ€™s part of the fun!

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Yeah it looked like someone whacked that tree a dozen times with a cheap machete.

OK so what do Limeys call a vacuum cleaner?

And how come with all that technology, reality ends up looking like â€śLawnmower Man?â€ť

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Iâ€™m not positive but Iâ€™ve heard Brits refer to them as a â€śHooverâ€ť before, using the brand name in a generic fashion in a similar manner to how in the US most refer to a photo copy as a â€śXeroxâ€ť.

Yep.

Even though Hoover UK went down the pan after an ill-advised â€śfree flights with a vacuum/washing machine purchaseâ€ť promotion, the name persists.

Some small part of me saw the shape of the warped CD and thought that it could be a setup for some sort of math or physics problem. It might be interesting to see if the shape of the waveform changes with 50 Hz vs 60 Hz mains current. Would it be possible to spin the CD even faster with a lower-vibration spindle constructed to better specifications? Or was the observed warping a fundamental limitation of the disc materials?

Yes, yes, three times yes on that.

Unlikely, the motor in question was not likely to be the synchronous kind. Would run more or less at the same speed at either mains frequency.

Possibly.

My guess is that it was interaction with the air, where a small instability formed a â€świngâ€ť that exercised an aerodynamic pull in the outward direction, and/or the elastic deformation of the material due to the centrifugal force.

Rerunning the experiment in vacuum (or at least at significantly lower pressure) could answer if the aerodynamic effects play a role. The effects of air viscosity could be also gauged by replacing air with helium or hydrogen for lighter, lower-viscosity gas, or with sulfur hexafluoride or a suitable freon for the other extreme.