Circular motion can occur in two possible directions. A clockwise (typically abbreviated as CW) motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top. In a mathematical sense, a circle defined parametrically in a positive Cartesian plane by the equations x = sin t and y = cos t is traced clockwise as t increases in value. Described another way, continually turning right is clockwise motion, as viewed from above. The opposite sense of rotation or revolution is (in American English) counterclockwise (CCW), or (in British English) anticlockwise (ACW).
The terms clockwise and counterclockwise can only be applied to a rotational motion once a side of the rotational plane is specified, from which the rotation is observed. For example, the daily rotation of the Earth is counterclockwise when viewed from above the North Pole, and clockwise when viewed from above the South Pole.
Clocks traditionally follow this sense of rotation because of the clock's predecessor: the sundial. Clocks with hands were first built in the Northern Hemisphere (see main article), and they were made to work like sundials. In order for a horizontal sundial to work (in the Northern Hemisphere), it must be placed looking southward. Then, when the Sun moves in the sky (east to south to west), the shadow cast on the opposite side of the sundial moves with the same sense of rotation (west to north to east). This is why hours were drawn in sundials in that manner, and why modern clocks have their numbers set in the same way. Note, however, that on a vertical sundial (such as those placed on the walls of buildings), the shadow moves in the opposite direction, and some clocks were constructed to mimic this. The best-known surviving example is the astronomical clock in the Münster Cathedral, whose hands move counterclockwise.
Occasionally, clocks whose hands revolve counterclockwise are nowadays sold as an aid to the left-handed, or as a novelty. Historically, some Jewish clocks were built that way, for example in some synagogue towers in Europe. This was done in accordance with the right-to-left reading direction of the Hebrew language.
Typical nuts, screws, bolts, and bottle caps are tightened (moved away from the observer) clockwise and loosened (moved towards the observer) counterclockwise, in accordance with the right-hand rule.
A way of remembering this that is based on the right-hand rule is to place one's loosely-clenched right hand above the object with the thumb pointing in the direction one wants the screw, nut, bolt, or cap ultimately to move, and the curl of the fingers, from the palm to the tips, will indicate in which way one needs to turn the screw, nut, bolt or cap to achieve the desired result. Most threaded objects are susceptible to application of the above; for a countably small number of exceptions (read: "left-handed" threads, or "reverse threads"), one substitutes the left-hand rule instead.
The reason for the clockwise orientation of most screws and bolts is that supination of the arm, which is used by a right-handed person to turn a screw clockwise, is generally stronger than pronation. Also, it was wise to adopt a single standard version for most screws and bolts – in order to eliminate endless confusion.
Sometimes the opposite sense of threading is used for a special reason. A thread might need to be left-handed to prevent the prevalent stresses that are present from loosening it. For example, some older automobiles and trucks had right-handed lug nuts on the right side of the vehicle and left-handed lug nuts on the left side of the vehicle. As the vehicle moved forward, the lug nuts tend to tighten. For a pair of bicycle pedals, for instance, one must be reverse-threaded, or the pedal will fall off; similarly, the flyer whorl of a spinning wheel uses a left-hand thread to keep from loosening in normal use. A turnbuckle has right-handed threads on one end and left-handed threads on the other end. Some gas fittings are left-handed to prevent disastrous misconnections. For example, oxygen fittings are right-handed, but acetylene and other flammable gases use left-handed fittings.
In trigonometry, and in mathematics in general, plane angles are conventionally measured counterclockwise, starting with 0° or 0 radians pointed directly to the right (or east). In navigation, compass headings increase in a clockwise direction around the compass face, starting with 0° at the top of the compass (the northerly direction).
Category:Fundamental physics concepts Category:Orientation
bg:Посока на часовниковата стрелка ca:Sentit horari de:Drehrichtung hi:दक्षिणावर्त es:Sentido del reloj fa:ساعتگرد و پادساعتگرد fr:Sens trigonométrique he:כיוון השעון it:Senso orario nl:Wijzerzin ja:時計回り pl:Prawoskrętność pt:Sentido dos ponteiros do relógio ro:Sens orar ru:По часовой стрелке и против часовой стрелки simple:Clockwise fi:Myötäpäivä sv:Med- och moturs zh:順時針方向This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
The World News (WN) Network, has created this privacy statement in order to demonstrate our firm commitment to user privacy. The following discloses our information gathering and dissemination practices for wn.com, as well as e-mail newsletters.
We do not collect personally identifiable information about you, except when you provide it to us. For example, if you submit an inquiry to us or sign up for our newsletter, you may be asked to provide certain information such as your contact details (name, e-mail address, mailing address, etc.).
When you submit your personally identifiable information through wn.com, you are giving your consent to the collection, use and disclosure of your personal information as set forth in this Privacy Policy. If you would prefer that we not collect any personally identifiable information from you, please do not provide us with any such information. We will not sell or rent your personally identifiable information to third parties without your consent, except as otherwise disclosed in this Privacy Policy.
Except as otherwise disclosed in this Privacy Policy, we will use the information you provide us only for the purpose of responding to your inquiry or in connection with the service for which you provided such information. We may forward your contact information and inquiry to our affiliates and other divisions of our company that we feel can best address your inquiry or provide you with the requested service. We may also use the information you provide in aggregate form for internal business purposes, such as generating statistics and developing marketing plans. We may share or transfer such non-personally identifiable information with or to our affiliates, licensees, agents and partners.
We may retain other companies and individuals to perform functions on our behalf. Such third parties may be provided with access to personally identifiable information needed to perform their functions, but may not use such information for any other purpose.
In addition, we may disclose any information, including personally identifiable information, we deem necessary, in our sole discretion, to comply with any applicable law, regulation, legal proceeding or governmental request.
We do not want you to receive unwanted e-mail from us. We try to make it easy to opt-out of any service you have asked to receive. If you sign-up to our e-mail newsletters we do not sell, exchange or give your e-mail address to a third party.
E-mail addresses are collected via the wn.com web site. Users have to physically opt-in to receive the wn.com newsletter and a verification e-mail is sent. wn.com is clearly and conspicuously named at the point of
collection.If you no longer wish to receive our newsletter and promotional communications, you may opt-out of receiving them by following the instructions included in each newsletter or communication or by e-mailing us at michaelw(at)wn.com
The security of your personal information is important to us. We follow generally accepted industry standards to protect the personal information submitted to us, both during registration and once we receive it. No method of transmission over the Internet, or method of electronic storage, is 100 percent secure, however. Therefore, though we strive to use commercially acceptable means to protect your personal information, we cannot guarantee its absolute security.
If we decide to change our e-mail practices, we will post those changes to this privacy statement, the homepage, and other places we think appropriate so that you are aware of what information we collect, how we use it, and under what circumstances, if any, we disclose it.
If we make material changes to our e-mail practices, we will notify you here, by e-mail, and by means of a notice on our home page.
The advertising banners and other forms of advertising appearing on this Web site are sometimes delivered to you, on our behalf, by a third party. In the course of serving advertisements to this site, the third party may place or recognize a unique cookie on your browser. For more information on cookies, you can visit www.cookiecentral.com.
As we continue to develop our business, we might sell certain aspects of our entities or assets. In such transactions, user information, including personally identifiable information, generally is one of the transferred business assets, and by submitting your personal information on Wn.com you agree that your data may be transferred to such parties in these circumstances.