Speed

Information about Speed

This article is about speed in physics. For other uses, see Speed (disambiguation).

Speed is the rate of motion, or equivalently the rate of change in position, many times expressed as distance d traveled per unit of time t.

Speed is a scalar quantity with dimensions distance/time; the equivalent vector quantity to speed is known as velocity. Speed is measured in the same physical units of measurement as velocity, but does not contain the element of direction that velocity has. Speed is thus the magnitude component of velocity.

In mathematical notation, it is simply:

Note that "S" is speed.

Objects that move horizontally as well as vertically (such as aircraft) distinguish forward speed and climbing speed.

Units

Units of speed include:

meters per second, (symbol m/s), the SI derived unit
centimeters per second, (symbol cm/s)
kilometers per hour, (symbol km/h)
miles per hour, (symbol m/h)
knots (nautical miles per hour, symbol kt)
Mach, where Mach 1 is the speed of sound; Mach n is n times as fast.

:Mach 1 ≈ 343 m/s ≈ 1235 km/h ≈ 768 mph (see the speed of sound for more detail)

speed of light in vacuum (symbol c) is one of the natural units

:c = 299,792,458 m/s

Other important conversions

:1 m/s = 3.6 km/h

:1 mph = 1.609 km/h

:1 knot = 1.852 km/h = 0.514 m/s

Vehicles often have a speedometer to measure the speed.

Average speed

Speed as a physical property represents primarily instantaneous speed. In real life we often use average speed (denoted $\text{[math]}$ ), which is rate of total distance (or length) and time interval. For example, if you go 60 miles in 2 hours, your average speed during that time is 60/2 = 30 miles per hour, but your instantaneous speed may have varied.

In mathematical notation:

Instantaneous speed defined as a function of time on interval $\text{[math]}$ gives average speed:

$\text{[math]}$

while instant speed defined as a function of distance (or length) on interval $\text{[math]}$ gives average speed:

$\text{[math]}$

It is often intuitively expected, but incorrect, that going half a distance with speed $\text{[math]}$ and second half with speed $\text{[math]}$ , produces total average speed $\text{[math]}$ . The correct value is $\text{[math]}$
(Note that the first is a proper arithmetic mean while the second is a proper harmonic mean).

Average speed can be derived also from speed distribution function (either in time or on distance):

Examples of different speeds

Below are some examples of different speed (see also main article Orders of magnitude (speed)):

Speed of a common snail = 0.001 m/s; 0.0036 km/h; 0.0023 mph.
A brisk walk = 1.667 m/s; 6 km/h; 3.75 mph.
Olympic sprinters (average speed over 100 metres) = 10 m/s; 36 km/h; 22.5 mph.
Speed limit on a French autoroute = 36.111 m/s; 130 km/h; 80 mph.
Top cruising speed of a Boeing 747-8 = 290.947 m/s; 1047.41 km/h; 650.83 mph; (officially Mach 0.85)
Official air speed record = 980.278 m/s; 3,529 km/h; 2,188 mph.
Space shuttle on re-entry = 7,777.778 m/s; 28,000 km/h; 17,500 mph.
the speed of sound in air (Mach 1) is about 340 m/s, and 1500 m/s in water
Taipei 101 Observatory Elevator = 1010 m/min ; 16.667 m/s ; 60.6 km/h; 37.6 mph

References

Weisstein, Eric W. "Speed." From MathWorld--A Wolfram Web Resource. [1]

Kinematics
← Integrate ... Differentiate → Displacement (Distance) \| Velocity (Speed) \| Acceleration \| Jerk \| Snap

Speed is the rate of motion, change, or activity.

Speed may also refer to:

In media, leisure and culture:

Speed (film), a 1994 American film starring Keanu Reeves and Sandra Bullock
Speed

..... Click the link for more information.

cite any references or sources. Please help improve this article by citing reliable sources.
* It is in need of attention from an expert on the subject. may be able to help recruit one.
* It needs to be expanded.
..... Click the link for more information.

Distance is a numerical description of how far apart objects are at any given moment in time. In physics or everyday discussion, distance may refer to a physical length, a period of time, or an estimation based on other criteria (e.g. "two counties over").
..... Click the link for more information.

units of measurement have played a crucial role in human endeavour from early ages up to this day. Disparate systems of measurement used to be very common. Now there is a global standard, the International System (SI) of units, the modern form of the metric system.
..... Click the link for more information.

time.

One view is that time is part of the fundamental structure of the universe, a dimension in which events occur in sequence, and time itself is something that can be measured.
..... Click the link for more information.

scalar is a simple physical quantity that does not depend on direction, and is therefore not changed by coordinate system rotations (in Newtonian mechanics), or by Lorentz transformations (in relativity). (Contrast to vector.
..... Click the link for more information.

Quantity is a kind of property which exists as magnitude or multitude. It is among the basic classes of things along with quality, substance, change, and relation. Quantity was first introduced as quantum, an entity having quantity.
..... Click the link for more information.

dimension (Latin, "measured out") is a parameter or measurement required to define the characteristics of an object—i.e., length, width, and height or size and shape.
..... Click the link for more information.

Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end. This may be distinguished from height, which is vertical extent, and width or breadth
..... Click the link for more information.

spatial vector, or simply vector, is a concept characterized by a magnitude and a direction. A vector can be thought of as an arrow in Euclidean space, drawn from an initial point A pointing to a terminal point B.
..... Click the link for more information.

velocity is defined as the rate of change of position. It is a vector physical quantity, both speed and direction are required to define it. In the SI (metric) system, it is measured in meters per second (m/s). The scalar absolute value (magnitude) of velocity is speed.
..... Click the link for more information.

For other senses of this word, see magnitude.

The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which
..... Click the link for more information.

aircraft is a vehicle which is able to fly through the air (or through any other atmosphere). All the human activity which surrounds aircraft is called aviation. (Most rocket vehicles are not aircraft because they are not supported by the surrounding air).
..... Click the link for more information.

V speeds (aircraft) are speeds that define certain performance and limiting characteristics of an aircraft and the "V" stands for velocity. They are established by the manufacturer during design and testing, and are specific to the aircraft model.
..... Click the link for more information.

Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector quantity which specifies both magnitude and a specific direction), defined by distance in metres divided by time in seconds.
..... Click the link for more information.

SI derived units are part of the SI system of measurement units and are derived from the seven SI base units.

Dimensionless derived units

The following SI units are actually dimensionless ratios, formed by dividing two identical SI units.
..... Click the link for more information.

Kilometres per hour (American English: kilometers per hour) is a unit of both speed (scalar) and velocity (vector). The unit symbol is km/h or km·h⁻¹
..... Click the link for more information.

Miles per hour is a unit of speed, expressing the number of international miles covered per hour.

Miles per hour is the unit used for speed limits, and speeds, on roads in the United Kingdom, United States and some other nations, where it is commonly abbreviated in everyday
..... Click the link for more information.

knot is a unit of speed. The abbreviation preferred by maritime authorities in the USA^[1], and Canada ^[2], as well as the Institute of Electrical and Electronics Engineers and the International Bureau of Weights and Measures is kn.
..... Click the link for more information.

1 nautical mile =
SI units
0 m 0 km
US customary / Imperial units
0 ft 0 mi

A nautical mile or sea mile is a unit of length.
..... Click the link for more information.

Mach number (Ma) (pronounced: [mɑːk], [mɑx], [mæk], see IPA) is a dimensionless measure of relative speed.
..... Click the link for more information.

speed of sound describes how much distance such a wave travels in a given amount of time. In dry air, at a temperature of 21 °C (70 °F) the speed of sound is 344 m/s (1238 km/h, or 769 mph, or 1128 ft/s).
..... Click the link for more information.

speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning "swiftness".^[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum.
..... Click the link for more information.

A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than standard atmospheric pressure. The Latin term in vacuo is used to describe an object as being in what would otherwise be a vacuum.
..... Click the link for more information.

In physics, natural units are physical units of measurement defined in terms of universal physical constants in such a manner that some chosen physical constants take on the numerical value of one when expressed in terms of a particular set of natural units.
..... Click the link for more information.

speedometer is a vehicle instrument that measures the instantaneous speed.

Traditional automotive speedometers are driven by a flexible, sleeved cable that is rotated by a set of small gears in the tail shaft of a transmission.
..... Click the link for more information.

A physical property is any aspect of an object or substance that can be measured or perceived without changing its identity~~. Physical properties~~ can be intensive or extensive.
..... Click the link for more information.

This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.

Herod_Archelaus

iPedia Free Information Center