- This article deals with the unit of force. For the unit of mass see Pound (mass). The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass
The pound-force or simply pound (abbreviations: lb, lbf, or lbf) is a unit of force. In Physics, a force is whatever can cause an object with Mass to Accelerate.
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Definitions
The pound-force is approximately equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from place to place by up to half a percent) can safely be neglected. Earth's gravity, denoted by g, refers to the Gravitational attraction that the Earth exerts on objects on or near its surface [1]
The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed. Today, in accordance the General Conference on Weights and Measures, standard gravity is usually taken to be 9. The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures ( CGPM, never GCWM Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level 80665 m/s² (approximately 32. 17405 ft/s²)[2][3] but other values have been used, including 32. 16 ft/s² (approximately 9. 80237 m/s²). [4]
From the acceleration of the standard gravitational field and the international avoirdupois pound, we arrive at the following definition:[5]
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1 pound-force ≡ 0. 45359237 kg × 9. 80665 m/s² = 4. 4482216152605 N (exactly)
Sixteen avoirdupois ounces (as a unit of mass) are equal to one avoirdupois pound (as a unit of mass). The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical This article is about the unit of mass For the unit of force see Pound-force. Similarly one ounce-force is equal to a sixteenth of a pound-force.
| newton (SI unit) |
dyne | kilogram-force, kilopond |
pound-force | poundal | |
|---|---|---|---|---|---|
| 1 N | ≡ 1 kg·m/s² | = 105 dyn | ≈ 0. The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical The unit kilogram-force ( kgf, often incorrectly just kg) or kilopond ( kp) is defined as the Force exerted by Earth's gravity The poundal is a non- SI unit of Force. It is a part of the Foot-pound-second system of units a coherent subsystem of English units introduced 10197 kp | ≈ 0. 22481 lbf | ≈ 7. 2330 pdl |
| 1 dyn | = 10−5 N | ≡ 1 g·cm/s² | ≈ 1. 0197×10−6 kp | ≈ 2. 2481×10−6 lbf | ≈ 7. 2330×10−5 pdl |
| 1 kp | = 9. 80665 N | = 980665 dyn | ≡ gn·(1 kg) | ≈ 2. 2046 lbf | ≈ 70. 932 pdl |
| 1 lbf | ≈ 4. 448222 N | ≈ 444822 dyn | ≈ 0. 45359 kp | ≡ gn·(1 lb) | ≈ 32. The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass 174 pdl |
| 1 pdl | ≈ 0. 138255 N | ≈ 13825 dyn | ≈ 0. 014098 kp | ≈ 0. 031081 lbf | ≡ 1 lb·ft/s² |
| The value of gn as used in the official definition of the kilogram-force is used here for all gravitational units. A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level | |||||
Use of pound as a unit of force
In some contexts, such as structural engineering applications, the term "pound" is used almost exclusively to refer to the unit of force and not the unit of mass. In those applications, the preferred unit of mass is the slug, i. The slug is an English unit of Mass. It is a mass that accelerates by 1 ft/s² when a force of one Pound-force (lbf is exerted on it e. lbf·s²/ft. In other contexts, the unit "pound" refers to a unit of mass. The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass In circumstances where there may be ambiguity otherwise, the symbols "lbf" and "lbm" and the terms "pounds-force" and "pounds-mass" can be used to distinguish.
Three common, equally valid foot-pound-second (fps) systems of units for doing calculations with mass and force are summarized in the table below, which also includes the corresponding metric units.
| System | Gravitational | Engineering | Absolute | |||
|---|---|---|---|---|---|---|
| Force (F) | F = m·a | F = m·a/gc = w·a/g | F = m·a | |||
| Weight (w) | w = m·g | w = m·g/gc ≈ m | w = m·g | |||
| Units | English | Metric | English | Metric | English | Metric |
| Acceleration (a) | ft/s2 | m/s2 | ft/s2 | m/s2 | ft/s2 | m/s2 |
| Mass (m) | slug | hyl | pound-mass | kilogram | pound | kilogram |
| Force (F) | pound | kilopond | pound-force | kilopond | poundal | newton |
In the "engineering" fps system, the weight of the mass unit (pound-mass) on Earth's surface is approximately equal to the force unit (pound-force). Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the The slug is an English unit of Mass. It is a mass that accelerates by 1 ft/s² when a force of one Pound-force (lbf is exerted on it In the gravitational metric system(s the base unit of force is not normalised to one mass unit ( Gram or Kilogram) times one length unit ( Metre or centimetre The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass The unit kilogram-force ( kgf, often incorrectly just kg) or kilopond ( kp) is defined as the Force exerted by Earth's gravity The poundal is a non- SI unit of Force. It is a part of the Foot-pound-second system of units a coherent subsystem of English units introduced The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical In the Physical sciences weight is a Measurement of the gravitational Force acting on an object The price for this convenience is that the force unit is not equal to the mass unit multiplied by the acceleration unit[6]—the use of Newton's Second Law, F = ma, requires another factor, gc, usually taken to be 32. Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the 17405 lb·ft/(lbf·s²). The "gravitational" fps system is a coherent system of units: by using the slug as the unit of mass, it avoids the need for such a constant. The "absolute" system is similarly coherent; the SI units are those of the "absolute" metric system.
See also
- Weight for a more complete discussion of customary units of force and mass
- Pounds per square inch, a unit of pressure
- Foot-pounds, a unit of work (energy), or torque
- Mass versus weight for the difference between the two physical properties
- Pound-mass
Notes and references
- ^ Acceleration due to gravity varies over the surface of the Earth, generally increasing from about 9. In the Physical sciences weight is a Measurement of the gravitational Force acting on an object The pound per square inch or more accurately pound-force per square inch (symbol psi or lbf/in² or lbf/in²) is a unit of Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The foot-pound force, or simply foot-pound (symbol ft·lbf or ft·lb) is a unit of work or Energy (a scalar In the physical sciences, Mass and Weight are different properties The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass 78 m/s² (32. 1 ft/s²) at the equator to about 9. 83 m/s² (32. 3 ft/s²) at the poles.
- ^ In 1901 the third CGPM declared (second resolution) that: "The value adopted in the International Service of Weights and Measures for the standard acceleration due to Earth's gravity is 980. 665 cm/s², value already stated in the laws of some countries. " This value was the conventional reference for calculating the kilogram-force, a unit of force whose use has been deprecated since the introduction of SI. The unit kilogram-force ( kgf, often incorrectly just kg) or kilopond ( kp) is defined as the Force exerted by Earth's gravity
- ^ Barry N. Taylor, Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811, Appendix B note 24
- ^ J. Edmond Shrader, Physics for Students of Applied Science, McGraw Hill, 1st ed. , 1937, p. 24.
- ^ The international avoirdupois pound is defined to be exactly 0. 45359237 kg.
- ^ The acceleration unit is the distance unit divided by the time unit squared.
Dictionary
pound-force
-noun
- A unit of force equal to a mass of one avoirdupois pound times a standard acceleration of gravity, equal to about 4.44822 newtons. Symbol lbf or lbf.
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