CD Shattering at 170,000FPS! - The Slow Mo Guys

What people said

Recommends Schwern · 2015-10 · Physics Stack Exchange · on “Why does public mains power use 50-60 Hz and 100-240 V?”

Why is mains frequency 50Hz and not 500 or 5? Engine efficiency, rotational stress, flicker, the skin effect, and the limitations of 19th century material engineering. 50Hz corresponds to 3000 RPM. That range is a convenient, efficient speed for the steam turbine engines which power most generators [LINK] and thus avoids a lot of extra gearing. 3000 RPM is also a fast, but doesn't put too much mechanical stress on the rotating turbine nor AC generator. 500Hz would be 30,000 RPM and at that speed your generator would likely tear itself apart. Here's what happens when you spin a CD at that speed [this video] , and for funsies at 62,000 FPS [this video] and 170,000 FPS [this video] . Why not slower? Flicker.

Cites zzzzBov · 2015-03 · Physics Stack Exchange · on “Could I break the sound barrier using circular motion? (And potentially create a sonic boom?)”

The Slow Mo Guys recently released a video of a CD shattering [this video] . I did some quick math, and it seems that a point on the edge of the CD would be travelling at around 144m/s at its breaking RPM (23,000RPM according to the video). It's still 200m/s shy of the sound barrier, but 42% is still impressively fast.

Cites Svj0hn · 2015-10 · Physics Stack Exchange · on “Why does public mains power use 50-60 Hz and 100-240 V?”

"The Slow Mo Guys" made a nice video about CD's shattering at high speed. The best footage is available here [this video]

Cites 404success · 2016-05 · Physics Stack Exchange · on “When this CD is spun so fast that it shatters, why does the warped shape move slower than the surface?”

In this video [this video] where a CD is spun abnormally fast to the point of shattering, one notices from the writing on the CD that the surface is spinning faster than the warp "shape" is. In other words, the shape the CD has warp into is moving in a circle, but not quite as fast as the surface of the CD. What's the explanation behind this de-synchronization? I would expect the warp shape to either not spin much at all, or spin at the same speed as the surface of the CD.

Cites Kosta Butbaia · 2016-09 · Physics Stack Exchange · on “What force acts on a small piece of a free, spinning ring?”

Centripetal force is provided by molecular bonds holding the ring together, If these molecular bonds aren't strong enough to hold for a specific angular velocity $\omega$ and you spun it up at that $\omega$ angular velocity it will break ( See this video [this video] of disk actually breaking because of this). For visualization suppose that ring is made out of rubber (can stretch easily) and you spin it, it's radius will increase because it's molecular bonds aren't strong enough to provide centripetal acceleration which is essential to circular motion, by increasing the radius it provides more force through tension. [LINK] Source [LINK] Mathematically centripetal force must equal Tension Force so

Cites inf3rno · 2018-01 · Physics Stack Exchange · on “Why does a rotating flexible disk have wave shape?”

I found a video [this video] on which they shatter CD with a high RPM tool. Before the CD shatters it has a wavy shape, so I guess an axial force shatters the CD instead of a radial force, probably some kind of vibration. Am I right, or something completely different happens here?

Cites James · 2018-05 · Physics Stack Exchange · on “Inertia on a rotating disc?”

From Newton's laws, we know that an object in motion will travel in a straight line unless acted upon an external force. On the merry-go-round, you are constantly changing direction; i.e., your direction is always tangential to the center of rotation. If you draw a velocity vector at different times on the merry-go-round you will see this clearly. Thus the moment you release the ball it continues in a straight line, with its initial velocity, tangential to the center of rotation at the moment of release. There is something called "rotational inertia" more commonly referred to the " moment of inertia [LINK] ", however, it is not as you describe. It a measurement of the inertia of a rotating o

Cites null · 2018-11 · Physics Stack Exchange · on “How does an isolated body in deep space 'know' it's rotating?”

@chaslyfromUK The acceleration relative to other parts of the same body. The centrifugal force depends on the distance from the axis of rotation. As different parts of the body have different distances to the axis of rotation, they would experience different forces (not only in value, but also in direction). If you spin any body fast enough, it will be torn apart by those forces (or rather the difference between them). Just search for videos showing shattering CDs at high speeds [this video] . This wouldn't be any different in outer space.

Cites Cort Ammon · 2020-10 · Physics Stack Exchange · on “Does the centrifugal force exist in inertial frames too?”

The centrifugal force is a pseudoforce. It is not actually a real force. Others have mentioned this of course, but no answer would be complete without it. Now let's think about this problem in the inertial frame, while rotating. You have an object in motion. It wishes to stay in motion. If no outside forces (electrostatic forces, in this case) were to oppose it, it would continue going in a straight line. But you didn't want it to go in a straight line. You wanted it to go in a circular path. In order to do this, you use the string to apply a force to the mass. You move the molecules in the string such that the electrostatic forces applied enough force on the mass to put it on a circular pat

Cites George Menoutis · 2021-04 · Physics Stack Exchange · on “Strange pattern on fast spinning CD”

In the following youtube video and timestamp: [this video] one can see a cd spinning very quickly, in slow motion, just before it breaks. I'm not sure I understand what I see, much less the underlying principle. The shape of the cd, which looks like a "rotational wave", seems to be spinning much slower than the cd itself! What is happening there?