What makes a disk spin

A disc is like a gyroscope in that it uses gyroscopic inertia, the tendency of a gyroscope to keep spinning in the same plane without twisting and turning. With no spin, a disc is inherently unstable, and with no speed, no lift is generated, so a combination of these factors is needed for a disc to fly. The exact combination varies significantly from disc to disc, since different discs have different "wing" shapes.

Combining the wing and the gyroscope also introduces other factors, as the two are not mutually independent. The most obvious one is a torque on the disc. If the disc is spinning clockwise and moving forward when viewed from the top, then the left side of the disc is moving faster than the right side. There is a corresponding pressure drop over the left side and that side will produce greater lift, and the disc will try to twist clockwise when viewed from behind.

As mentioned above, the gyroscopic inertia acts to counter this, and the greater the spin, the higher the inertia. There is almost never any reason for not trying to put as much spin as possible on a disc, all other factors being equal. Spin provides stability, so that the disc will continue to fly in the direction it is already flying.

A disc that is lacking in spin will tend to "turn over", that is, twist about the axis of flight, and will generally not go as far as one which has more spin. Lack of spin is probably one of the two major problems encountered when trying to throw accurately over any reasonable distance.

One time when too much spin is possible is when throwing some golf discs. Their flight characteristics are such that they have a very narrow window of stability. Too much spin and they can twist one way, and too little spin and they will twist the other.

In general, however, too much spin is better countered by other factors in the throw, such as speed and angle of release, rather than by simply spinning the disc less. Particular discs are termed "overstable", "stable", and "understable" depending on how they to spin and speed.

A disc which needs a lot of spin to be stable at a given speed is called "understable", while a disc which needs little spin to be stable at a given speed is called "overstable". Most discs can be thrown "understably" or "overstably" by decreasing or increasing the amount of spin put on the disc. The speed of a disc is a major but not the only factor in determining how far a disc goes and how quickly it gets there. Unlike spin, it is possible to put too much speed on a disc.

The stability of a disc changes as it gets faster, and the stable range of the disc is determined both by the shape of the disc and its spin rate. Most discs used for throwing to other people are stable, that is, they fly flat at a range of speeds. Golf discs on the other hand are usually not very stable - they tend to fly flat only for brief periods during their flight.

The rest of the time they are banked either one way or the other. A generally stable disc thrown with too much speed in relation to the spin will act understably. That is, it will turn over. For this reason, hucking the disc requires plenty of spin and speed. View Full Term. By clicking sign up, you agree to receive emails from Techopedia and agree to our Terms of Use and Privacy Policy.

A spinning disk is the mechanism within a hard disk drive to which memory is written. With rotating plates attached to an arm that writes the data, the spinning disk mechanism physically resembles a record player although it is sealed within an enclosure. The plates are magnetized similarly to cassette tapes in order to store data that is written using copper heads.

Spinning disk technology has been arguably the most popular form of computer storage for decades, but has been increasingly superseded by solid state drives which are particularly common in newer notebooks and laptops in recent years. Nevertheless, the older hard disk technology has dramatically increased its storage throughout the years.

In spite of its constant physical size and uniform form factor, higher precision and sophisticated design has allowed the spinning disk hard drive to increase its capacity into the terabyte range. By: Justin Stoltzfus Contributor, Reviewer. By: Satish Balakrishnan. However, every now and then the hard disk spins up even if what I am doing in that moment has no clear link with data that are stored there. It is still a consequence of an action done by me, not of a cron script or something else, because it still happens as a consequence of my doing something, like opening an application.

However I cannot see what opening that application should produce an access to the spinning disk, knowing which file are supposed to be there. So I would like to understand more of what happens, and this justifies the question above. EDIT After some time I discovered there is a nice utility called fatrace that makes everything easier because you do not have to mess with services and devices: just call fatrace and you will see a log of all file accesses going on.

If you want to see only a certain device, just grep its mount point, or change dir to the mount point and use the -c flag. The following instructions are for a Debian system, but others will probably be very similar. This might help to find which process is causing the hard disk to spin up. The log is probably very verbose and might fill up the disk quite quickly. Once you're done, you can shut down auditd :.

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