Why do cds spin

Can science help explain why it cracks in this way, and so quickly? Centrifugal force is that which causes your arms to fling out when you spin around. This causes the disc to stretch, with the energy of the motion being converted into elastic energy, like that stored in a rubber band. But because the disc's polycarbonate material is rather brittle, it can't stretch much, and so the elastic energy leads stress to build up. At high speeds, it also becomes slightly uneven, like an askew car tire, and begins to wobble or vibrate, says Huseyin Sehitoglu , a mechanical engineer at the University of Illinois.

This adds to to the growing stress. Here is a fairly complete list:. There are several different formats used to store data on a CD, some widely used and some long-forgotten. Sign up for our Newsletter! Mobile Newsletter banner close.

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How CDs Work. Have you ever wonder how compact discs work? Understanding the CD: Material " ". Understanding the CD: The Spiral " ". Understanding the CD: Bumps " ". CD Player Components " ". A drive motor spins the disc. This drive motor is precisely controlled to rotate between and rpm depending on which track is being read. A laser and a lens system focus in on and read the bumps. A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track.

The tracking system has to be able to move the laser at micron resolutions. CD Encoding Issues " ". Because the laser is tracking the spiral of data using the bumps, there cannot be extended gaps where there are no bumps in the data track. To solve this problem, data is encoded using EFM eight-fourteen modulation. Because the laser wants to be able to move between songs, data needs to be encoded into the music telling the drive "where it is" on the disc.

This problem is solved using what is known as subcode data. Subcode data can encode the absolute and relative position of the laser in the track, and can also encode such things as song titles. Because the laser may misread a bump, there need to be error-correcting codes to handle single-bit errors.

To solve this problem, extra data bits are added that allow the drive to detect single-bit errors and correct them. Because a scratch or a speck on the CD might cause a whole packet of bytes to be misread known as a burst error , the drive needs to be able to recover from such an event. This problem is solved by actually interleaving the data on the disc, so that it is stored non-sequentially around one of the disc's circuits. The drive actually reads data one revolution at a time, and un-interleaves the data in order to play it.

If a few bytes are misread in music, the worst thing that can happen is a little fuzz during playback.

When data is stored on a CD, however, any data error is catastrophic. Newest Oldest. Discs - approx. Like Save. DVDs spin at rpm when reading at the innermost starting edge, and slow down to rpm when reading the outermost edge end CDs also start at the innermost edge Those are for standard 1x speed and mutiply for speeds up to about 12x.

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