A continuous curve which does not result in a circle. Something may spiral inward, outward, or in a circular fashion but out of the plane of the original motion.

Found in nature in molluscs, world-wide in mysterious places (a widespread symbol whose meaning has often been lost). The main feature of phonograph records whose spirals were first wrapped around cylinders.

Not necessarily a curve. You could have a 'square' spiral, or triangular, or a combination.

A spiral is a continuous section of line that circles around a central point, either inward towards the center or outward from the center, but does not join itself. The line is often a hypothetical line, describing the path of an object or flow (see vortex).

It's a lot more interesting to try to specify what a spiral can't do than what it can. Can you have a spherical spiral? Can you have a spiral in which the ends don't overlap on any plane? Can you spiral in 2 dimensions? How about 4? How chaotic can a spiral be before it stops being a spiral?

I was actually looking forward to trying to describe a spiral in text... Good job, arfarf.

A spiral is a curve drawn from a fixed point steadily getting farther and farther away from the starting point.

With an Archimedean spiral the loops are spaced evenly (so if you draw a line from the center of it outwards it will cross the spiral at equal intervals) whereas with a Logarithmic spiral the loop size increases in a geometric sequence (most commonly using Fibonacci numbers so that if you draw a line from the center outwards it will cross the spiral at a distance of 1, 2, 3, 5, 8, 13...). Logarithmic Spirals using Fibonacci numbers are very commonly found in nature. I don't think I'm up to describing Fermat's Spiral, but that node has some very nice ascii art you can look at.

Also, in Football a ball passed or kicked with a spin which propels it further with more accuracy; the ball points the same direction throughout its flight. (http://www.firstbasesports.com/glossaries/ftbglos.htm)

Or a defect in the cleaved end face of an optical fiber in which the surface changes abruptly. (http://www.laurin.com/DataCenter/Dictionary/)

スパイラル (Spiral ~Bond of Inference~)

TV series, 25 episodes, by J.C. Staff and Sony

Spiral is in many ways another "normal person meets people with a horrible secret"-anime. It revolves around the young amateur detective Narumi Ayumu, whose brother mysteriously disappeared some years ago and left his wife with him.

Time passes, and Ayumu himself suddenly becomes entangled in his brother's investigation as an unexpected assasination attempt happens right next to him.

Now, together with his sister-in-law Narumi Madoka and school newspaper journalist and "perfect girlfriend" Yuizaki Hiyono, he must unveil the secret of the mysterious Blade Children to prevent more murders from happening and find his brother!

The plot(s) of the series is vaguely similar to something taken out of an Agatha Christie-novel, with the characters pursuing the ongoing mystery to unravel the probably totally unthinkable and equally unlikely solution. The way in which the characters some times ignore all human sense of reason to follow some sort of hidden pattern laid out by the scriptwriters can sometimes get too unlikely to be funny. Anyone who's watched Hikaru no Go, Love Hina or basically any hentai movie should know what I'm talking about.

This does in no way degrade the series' artistic value, though, and the main characters Ayumu and Hiyono's antics really make watching the series a worthwhile experience.

In aviation terms, a spiral is defined as when an aircraft is spinning towards the ground (like, in a really steep turn) and at the same time accelerating. As you can imagine this can be pretty dangerous, as within a matter of seconds you could potentially be at your aircraft's structural speed limit... ie: Go any faster, lose your wings. Scary stuff. This is why it is very important to learn what a spiral is, when it happens, what the early-warning symptoms are, and how to correct them quickly. You also have to know how to differentiate between a spiral and a spin (basically, you don't accelerate in a spin).

A spiral may look similar to a spin, but a quick check of your instruments should tell you that you are accelerating. After you experience a spin and a spiral in training you will see they feel quite different; they only look the same when you are looking out the window.

The spiral is in essence really only a steep turn. A very steep turn. For example, and aircraft could roll completely on its side, then you could pull back on the control column to get an even steeper turn. This is a spiral. Because the only surface providing lift is your Rudder (even that isn't producing much), you are falling quite rapidly while turning. The smaller the aircraft, the steeper the turn possible (as a general rule of thumb). A big 747 could also spiral, but it wouldn't feel the same as its turning radius is huge.

The trick is that you can get into that attitude and not realize it by doing a high speed stall, not recognize it, and smash the plane up real good. Entering a spin incorrectly on purpose may result in a spiral. Yanking the controls around too quickly while doing maneuvers may result in a spiral. Many things! Read the excellent node on stalls to see how to enter a high-speed stall.

Recovery from a spiral is simple if you realize that you are not in a spin:
• Close the throttle. This will reduce the amount of speed gained in the spiral and the recovery (as speed is your greatest enemy here).
• Roll the wings level. Most spirals will occur at odd attitudes, and the quickest way to stop the spiraling motion is to roll those wings level with the ailerons (this point is important because you use the rudder to roll out of a spin).
• Ease out of the dive. Do this by pulling back on the control column in a nice fluid motion that isn't too quick. If you pull back too quickly you might stall and enter another spiral, blackout, or just plain break the aircraft.
• Only apply power when you are sure doing so will not exceed the airspeed limits of the aircraft.
If you were to use the rudder to recover, thinking it was a spin, you would probably damage the aircraft and make the spiral even worse. Be careful!

Spi"ral (?), a. [Cf. F. spiral. See Spire a winding line.]

1.

Winding or circling round a center or pole and gradually receding from it; as, the spiral curve of a watch spring.

2.

Winding round a cylinder or imaginary axis, and at the same time rising or advancing forward; winding like the thread of a screw; helical.

3. Geom.

Of or pertaining to a spiral; like a spiral.

Spiral gear, or Spiral wheel Mach., a gear resembling in general a spur gear, but having its teeth cut at an angle with its axis, or so that they form small portions of screws or spirals. -- Spiral gearing, a kind of gearing sometimes used in light machinery, in which spiral gears, instead of bevel gears, are used to transmit motion between shafts that are not parallel. -- Spiral operculum, an operculum whih has spiral lines of growth. -- Spiral shell, any shell in which the whorls form a spiral or helix. -- Spiral spring. See the Note under Spring, n., 4.

Spi"ral (?), n. [Cf. F. spirale. See Spiral, a.]

1. Geom.

A plane curve, not reentrant, described by a point, called the generatrix, moving along a straight line according to a mathematical law, while the line is revolving about a fixed point called the pole. Cf. Helix.

2.

Anything which has a spiral form, as a spiral shell.

Equiangular spiral,a plane curve which cuts all its generatrices at the same angle. Same as Logarithmic spiral, under Logarithmic. -- Spiral of Archimedes, a spiral the law of which is that the generatrix moves uniformly along the revolving line, which also moves uniformly.