Clock Time Clocks Accurate Processes Physical Pendulum Century

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A clock (from the Latin cloca, " bell") is an instrument for measuring time. A clock can be a physical instrument (an especially accurate one is called a chronometer). The clock in its modern form (24 hour clock) has been in use since at least the 15th century. Clock can refer to an abstract system of time measurement (ed. see calendar for other measurements).

1 Purposes

Clocks are in homes and offices; smaller ones ( watches) are carried along; big ones are in public places, e.g. a train station or church. A small clock is also often permanently shown in a corner of computer displays or mobile phones.

A clock, by measuring time (e.g. in seconds). supplies a numerical comparison between the durations of different time intervals. For example, a clock will provide the ratio of the duration of one day to the duration of a different day (for example, the earth is spinning slower today than it did a billion years ago. If the earth's spin is used as a clock, each rotation will take exactly one day, by definition.)

The main purpose of a clock is not always to display the time. It may also be used to control a device according to time, e.g. an alarm clock, a VCR, or a time bomb (see: counter).

Computers depend on an accurate internal clock to allow synchronized processing.

1.1 Ideal uses

An ideal clock appropriately measures the ratio of the duration of natural processes, and thus will give the appropriate time measure for use in physical theories. Therefore, to define an ideal clock in terms of any physical theory would be circular. An ideal clock is more appropriately defined in relationship to the set of all physical processes.

This leads to the following definitions:

A clock is a recurrentA process is a naturally occurring or designed sequence of operations or events, possibly taking up time, space, expertise or other resource, which produces some outcome. A process may be identified by the changes it creates in the properties of one or mo, periodic processA process is a naturally occurring or designed sequence of operations or events, possibly taking up time, space, expertise or other resource, which produces some outcome. A process may be identified by the changes it creates in the properties of one or mo and a counter.
A good clock is one which, when used to measure other recurrent processes, finds many of them to be periodic.
An ideal clock is a clock (i.e., recurrent process) that makes the most other recurrent processes periodic.

This definition can be further improved by the consideration of successive levels of smaller and smaller error tolerances. While not all physical processes can be surveyed, the definition should be based on the set of physical processes which includes all individual physical processes which are proposed for consideration. Since atoms are so numerous and since, within current measurement tolerances, they all beat in a manner such that if one is chosen as periodic then the others are all deemed to be periodic also, it follows that atomic clockAn atomic clock is a type of clock that uses an atomic frequency standard as its counter. Early atomic clocks were masers with attached equipment. Today's best atomic frequency standards (or clocks) are based on more advanced physics involving caesium beas represent ideal clocks to within present measurement tolerances and in relation to all presently known physical processes. However, they are not so designated by fiat. Rather, they are designated as the current ideal clock because they are currently the best instantiation of the definition.

1.2 Navigation

Accurate navigationThis article concerns navigation in the sense of determination of position and direction on the surface of the Earth. See Navigation (disambiguation) for other meanings. There are several traditions of navigation . Polynesian navigation The Polynesian nav by ships beyond the sight of land depends on the ability to measure latitudeLatitude denoted φ, gives the location of a place on Earth north or south of the Equator. Latitude is an angular measurement ranging from 0° at the Equator to 90° at the poles. Usually, the difference in latitude largely affects the climate and/or wea and longitudeMap of Earth showing vertical lines of longitude Longitude sometimes denoted λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. Longitude is given as an angular measurement ranging from 0° at. Latitude is fairly easy to determine through celestial navigationCelestial navigation is a position fixing technique that was the first system devised to help sailors locate themselves on a featureless ocean. Celestial navigation uses angular measurements (sights) between the horizon and a common celestial object., but the measurement of longitude requires accurate measurement of time. This need was a major motivation for the development of accurate mechanical clocks. John Harrison created the first, highly accurate marine chronometers in the mid-18th century. The Noon gun in Cape Town still fires an accurate signal to allow ships to check their chronometers.

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1 Purposes

1.1 Ideal uses

1.2 Navigation

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