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4. Questions - Got a question about Pound Force then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
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6. Returns - still worried that even after all of the above your Pound Force wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
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8. Security - check for the yellow padlock on the Pound Force site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Pound Force, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
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A
pound or
pound-force (abbreviations:
lb,
lbf, or
lbf) is a Units of measurement of
force.
Pound is also the name of a
pound (mass). One pound-force is approximately equal to the gravitational force exerted on a mass of one
pound (mass) on the surface of
Earth.
The standard
standard gravity is usually taken to be 9.80665 m/s² (approximately 32.174 05 ft/s²) today,Barry N. Taylor,
Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811, Appendix B note 24 but other values have been used, including 32.16 ft/s² (approximately 9.80237 m/s²).J. Edmond Shrader,
Physics for Students of Applied Science, McGraw Hill, 1st ed., 1937, p. 24. The actual acceleration due to
gravity (Earth) varies from place to place, in general increasing from the equator (9.78 m/s²) to the poles (9.83 m/s²).
Equivalence to other units of force
A pound-force is the gravitational force exerted on a pound-mass in the standard gravitational field at Earth's surface which causes free falling bodies to accelerate at exactly 9.80665 m/s² (32.1742 ft/s²) (see relationships table). An international avoirdupois pound is exactly 453.59237 grams or 0.45359237 kg. This means that 1 pound-force is equal to (0.45359237 × 9.80665) newtons, or approximately 4.448222 newtons (conversely, 1 newton is 0.22481 pounds-force).The pound-force has the same relationship to the 'ounce' used as a unit of force as the pound (mass) has to the
ounce.
Use of the pound as a unit of force
In some contexts, the unit "pound" refers to a Pound (mass) (see Use in Commerce under Pound (mass)). However, in other contexts, by convention, the "pound" refers to a unit of force. In circumstances where there may be ambiguity otherwise, the symbol "lbf" or the term "pounds-force" can be used for the unit of force and the term "pounds-mass" ("lbm") can be used for the unit of mass.
For example, in structural engineering applications the term "pound" is used almost exclusively to refer to a unit of force and not to refer to the unit of mass. In those applications, the preferred unit of mass is the Slug (mass), i.e. lbf·s²/ft.
There are three practical ways of doing calculations with mass and force in the foot-pound-second (fps) systems (and other systems such as inch-pound-second systems not discussed here). Those three ways are summarized in the table below, which also sets out the corresponding position under the
International System of Units (SI).
{]|colspan="2"|
F = m·a|colspan="2"|
F = m·a/gc = w·a/g|colspan="2"|
F = m·a|-! Weight of an object|colspan="2"|
w = m·g|colspan="2"|
w = m·g/gc|colspan="2"|
w = m·g|-! Units! English || Metric! English || Metric! English || Metric|-! Time| second || second| second || second| second || second|-! Distance| foot || meter| foot || meter| foot || meter|-! Mass|
slug (mass) ||
hyl ] | pound-force || kilopond| poundal ],
gc, into the relationship between force on the one hand and mass and acceleration on the other hand. In this system, the weight of the mass unit (pound ) on Earth's surface is equal to the force unit (pound-force). The price for this convenience is that the force unit is no longer equal to the mass unit multiplied by the distance unit divided by the time unit squared (the use of
Newton's laws of motion,
F = ma, requires another factor,
gc). This gravitational constant is usually taken to be 32.17405 lb·ft/(lbf·s²). The required introduction of the constant
gc is a reason why many, including people in engineering fields, prefer the simpler "gravitational" fps system, and use the Slug (mass) as the unit of mass.
No one of the three fps systems is more correct than the other two.
Historical origins
Pounds-force had been used in low-precision measurements since the 18th century, but they were never well-defined units until the 20th century.
The second resolution of the third
General Conference on Weights and Measures (CGPM) in 1901 declared that: Resolution of the 3rd CGPM
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 the SI.
See also
- Weight for a more complete discussion of customary units of force and mass
- Pounds per square inch, a unit of pressure
- Foot-pound force, a unit of work (energy), or torque
References
A
pound or
pound-force (abbreviations:
lb,
lbf, or
lbf) is a
Units of measurement of
force.
Pound is also the name of a pound (mass). One pound-force is approximately equal to the gravitational force exerted on a mass of one pound (mass) on the surface of
Earth.
The standard standard gravity is usually taken to be 9.80665 m/s² (approximately 32.174 05 ft/s²) today,Barry N. Taylor,
Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811, Appendix B note 24 but other values have been used, including 32.16 ft/s² (approximately 9.80237 m/s²).J. Edmond Shrader,
Physics for Students of Applied Science, McGraw Hill, 1st ed., 1937, p. 24. The actual acceleration due to
gravity (Earth) varies from place to place, in general increasing from the equator (9.78 m/s²) to the poles (9.83 m/s²).
Equivalence to other units of force
A pound-force is the gravitational force exerted on a pound-mass in the standard gravitational field at Earth's surface which causes free falling bodies to accelerate at exactly 9.80665 m/s² (32.1742 ft/s²) (see relationships table). An international avoirdupois pound is exactly 453.59237 grams or 0.45359237 kg. This means that 1 pound-force is equal to (0.45359237 × 9.80665) newtons, or approximately 4.448222 newtons (conversely, 1 newton is 0.22481 pounds-force).The pound-force has the same relationship to the 'ounce' used as a unit of force as the
pound (mass) has to the ounce.
Use of the pound as a unit of force
In some contexts, the unit "pound" refers to a
Pound (mass) (see Use in Commerce under
Pound (mass)). However, in other contexts, by convention, the "pound" refers to a unit of force. In circumstances where there may be ambiguity otherwise, the symbol "lbf" or the term "pounds-force" can be used for the unit of force and the term "pounds-mass" ("lbm") can be used for the unit of mass.
For example, in structural engineering applications the term "pound" is used almost exclusively to refer to a unit of force and not to refer to the unit of mass. In those applications, the preferred unit of mass is the Slug (mass), i.e. lbf·s²/ft.
There are three practical ways of doing calculations with mass and force in the foot-pound-second (fps) systems (and other systems such as inch-pound-second systems not discussed here). Those three ways are summarized in the table below, which also sets out the corresponding position under the International System of Units (SI).
{]|colspan="2"|
F = m·a|colspan="2"|
F = m·a/gc = w·a/g|colspan="2"|
F = m·a|-! Weight of an object|colspan="2"|
w = m·g|colspan="2"|
w = m·g/gc|colspan="2"|
w = m·g|-! Units! English || Metric! English || Metric! English || Metric|-! Time| second || second| second || second| second || second|-! Distance| foot || meter| foot || meter| foot || meter|-! Mass|
slug (mass) || hyl ] | pound-force || kilopond|
poundal ],
gc, into the relationship between force on the one hand and mass and acceleration on the other hand. In this system, the weight of the mass unit (pound ) on Earth's surface is equal to the force unit (pound-force). The price for this convenience is that the force unit is no longer equal to the mass unit multiplied by the distance unit divided by the time unit squared (the use of Newton's laws of motion,
F = ma, requires another factor,
gc). This gravitational constant is usually taken to be 32.17405 lb·ft/(lbf·s²). The required introduction of the constant
gc is a reason why many, including people in engineering fields, prefer the simpler "gravitational" fps system, and use the
Slug (mass) as the unit of mass.
No one of the three fps systems is more correct than the other two.
Historical origins
Pounds-force had been used in low-precision measurements since the 18th century, but they were never well-defined units until the 20th century.
The second resolution of the third
General Conference on Weights and Measures (CGPM) in 1901 declared that: Resolution of the 3rd CGPM
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 the SI.
See also
- Weight for a more complete discussion of customary units of force and mass
- Pounds per square inch, a unit of pressure
- Foot-pound force, a unit of work (energy), or torque
References
Definition: pound force from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.
Pound-force - Wikipedia, the free encyclopedia
The pound-force or simply pound (abbreviations: lb, lbf, or lb f) is a unit of force.
Foot-pound force - Wikipedia, the free encyclopedia
The foot-pound force, or simply foot-pound (symbol: ft·lb f or ft·lb) is a unit of work or energy (a scalar) and also a unit of torque (a vector).
Pound-Force -- from Eric Weisstein's World of Physics
The British engineering unit of force, commonly simply called the "pound." However, because of colloquial usage of the term "pound" as a unit of mass (i.e., pound-mass), the ...
Foot-pound force definition of Foot-pound force in the Free Online ...
foot-pound, abbr. ft-lb, unit of work work, in physics and mechanics, transfer of energy by a force acting to displace a body. Work is equal to the product of the force and the ...
Definition: pound from Online Medical Dictionary
Previous: poultry handler's disease, poultryman's itch, poultry products, pounce Next: poundal, pound force, pound of steam, Poupart, Francois
Pound-force - definition of Pound-force in the Medical dictionary - by ...
foot-pound-second system. n. Abbr. fps system. The British, Canadian, or US system of units based on the foot, the pound, and the second as the fundamental units of length, mass ...
Pound Force - DiracDelta Science & Engineering Encyclopedia
Science Engineering Encyclopedia ... Pound Force. A derived unit of force in the British system of units. See also: Force.
pound-force - Wiktionary
Definition from Wiktionary, a free dictionary
pound-foot definition of pound-foot in the Free Online Encyclopedia.
pound-foot: see foot-pound foot-pound, abbr. ft-lb, unit of work or energy in the customary English gravitational system; it is the work done or energy expended by a force of 1 ...
