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Newton's Second Law

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In kinematics, the instantaneous speed of an object (denoted v) is the magnitude of its instantaneous velocity (the rate of change of its position); it is thus the scalar equivalent of velocity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero.

Like velocity, speed has the dimensions of a length divided by a time; the SI unit of speed is the meter per second, but the most usual unit of speed in everyday usage is the kilometer per hour or, in certain countries, the mile per hour.

The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in vacuum c = 299,792,458 meters per second, approximately 1079 million kilometers (671 million miles) per hour. Matter cannot quite reach the speed of light, as this would require an infinite amount of energy.

Definition

The instantaneous speed v is defined as the magnitude of the instantaneous velocity v, that is the derivative of the position r with respect to time:

If s is the length of the path traveled until time t, the speed equals the time derivative of sx:

Units

Units of speed include:

• meters per second, (symbol m s⁻¹ or m/s), the SI derived unit
• kilometers per hour, (symbol km/h)
• miles per hour, (symbol mph)
• knots (nautical miles per hour, symbol kt)
• Mach number, speed divided by the speed of sound
• speed of light in vacuum (symbol c) is one of the natural units

c = 299,792,458 m/s

(Values in bold face are exact.)

Examples of different speeds

• Speed of a common snail = 0.001 m/s; 0.004 km/h; 0.002 mph (1 millimeter per second).
• A brisk walk = 1.7 m/s; 6 km/h; 4 mph (5.5 feet per second).
• Olympic sprinters (average speed over 100 metres) = 10 m/s; 36 km/h; 22 mph.
• Speed limit on a French autoroute = 36 m/s; 130 km/h; 80 mph.
• Taipei 101 observatory elevator = 1010 m/min ; 16.7 m/s ; 60.6 km/h; 37.6 mph
• Cruising speed of a Boeing 747-8 = 290 m/s; 1050 km/h; 650 mph; (Mach 0.85)
• The speed of sound in dry air at sea-level pressure and 20 °C (293 kelvin) = 343 ms^-1 ≈ 1235 km/h ≈ 768 mph ( = Mach 1 by definition).
• Muzzle velocity of an AK47 assault rifle = 710 m/s; 2,600 km/h; 1,600 mph.
• Muzzle velocity of a paintball marker = 90 m/s; 320 km/h; 200 mph.
• Official flight airspeed record = 980 m/s; 3,530 km/h; 2,194 mph.
• Escape velocity on Earth: 11.2 km/s; 40,000 km/h; 25,000 mph
• Space shuttle on re-entry = 7,800 m/s; 28,000 km/h; 17,500 mph.
• Average orbital speed of planet Earth = 29,783 m/s; 107,218 km/h; 66,623 mph.
• Speed of light in vacuum (symbol c) 299,792,458 m/s (exactly, by definition of meter).

See also

• Air speed
• Land speed
• List of vehicle speed records
• Typical projectile speeds
• Speedometer
• V speeds

References

• Richard P. Feynman, Robert B. Leighton, Matthew Sands. The Feynman Lectures on Physics, Volume I, Section 8-2. Addison-Wesley, Reading, Massachusetts (1963). ISBN 0-201-02116-1.

Kinematics ← Integrate … Differentiate → Displacement (Distance) | Velocity (Speed) | Acceleration | Jerk | Jounce | Crackle and pop

From Wikiquote

This entry relates to the physical concept of speed; for the film, see Speed (1994 film)

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

Quotes

• But the speed was power, and the speed was joy, and the speed was pure beauty.
  • Richard Bach, Jonathan Livingston Seagull (1970).

• Be wise with speed;
  A fool at forty is a fool indeed.
  • Edward Young, Love of Fame, satire ii, line 282.

• Ease and speed in doing a thing do not give the work lasting solidity or exactness of beauty.
  • Plutarch, Life of Pericles.

External links

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Speed

Look up Speed in Wiktionary, the free dictionary

Definition from Wiktionary, a free dictionary

English

Etymology

Middle English sped (“‘good fortune’”).

Proper noun

Speed

1. A surname.

Anagrams

• Anagrams of deeps
• pedes

German

Noun

Speed n.

1. (slang) speed (type of drugs)