Specific force: Difference between revisions

Content deleted Content added

Inline

Latest revision as of 17:10, 27 September 2023

Specific force (SF) is a mass-specific quantity defined as the quotient of force per unit mass.

\mathrm {SF} =F/m

It is a physical quantity of kind acceleration, with dimension of length per time squared and units of metre per second squared (m·s⁻²).

It is normally applied to forces other than gravity, to emulate the relationship between gravitational acceleration and gravitational force. It can also be called mass-specific weight (weight per unit mass), as the weight of an object is equal to the magnitude of the gravity force acting on it.

The g-force is an instance of specific force measured in units of the standard gravity (g) instead of m/s², i.e., in multiples of g (e.g., "3 g").

Type of acceleration

The (mass-)specific force is not a coordinate acceleration, but rather a proper acceleration, which is the acceleration relative to free-fall. Forces, specific forces, and proper accelerations are the same in all reference frames, but coordinate accelerations are frame-dependent. For free bodies, the specific force is the cause of, and a measure of, the body's proper acceleration.

The acceleration of an object free falling towards the earth depends on the reference frame (it disappears in the free-fall frame, also called the inertial frame), but any g-force "acceleration" will be present in all frames. This specific force is zero for freely-falling objects, since gravity acting alone does not produce g-forces or specific forces.

Accelerometers on the surface of the Earth measure a constant 9.8 m/s^2 even when they are not accelerating (that is, when they do not undergo coordinate acceleration). This is because accelerometers measure the proper acceleration produced by the g-force exerted by the ground (gravity acting alone never produces g-force or specific force). Accelerometers measure specific force (proper acceleration), which is the acceleration relative to free-fall,^[1] not the "standard" acceleration that is relative to a coordinate system.

Hydraulics

In open channel hydraulics, specific force ( $F_{s}$ ) has a different meaning:

F_{s}={\frac {Q^{2}}{gA}}+zA

where Q is the discharge, g is the acceleration due to gravity, A is the cross-sectional area of flow, and z is the depth of the centroid of flow area A.^[2]

References

^ Savage, Paul G (May 8, 2005). "What Do Accelerometers Measure?" (PDF). Strapdown Associates, Inc.
^ Chaudhry, M. Hanif "Open Channel Flow" 2nd Ed. (2008) pg.31 ISBN 978-0-387-30174-7

This classical mechanics–related article is a stub. You can help Wikipedia by expanding it.

[1] Savage, Paul G (May 8, 2005). "What Do Accelerometers Measure?" (PDF). Strapdown Associates, Inc.

[2] Chaudhry, M. Hanif "Open Channel Flow" 2nd Ed. (2008) pg.31 ISBN 978-0-387-30174-7

[1]

[2]

@@ Line 1: / Line 1: @@
+{{Short description|Concept in physics}}
-'''Specific force''' is defined as the non-gravitational [[force]] per unit [[mass]].
+{{Confusing|reason=It's not clear at the end if specific force is proper acceleration or not. There's another Wikipedia article talking about proper acceleration|date=March 2017}}
-:<math>\mbox{Specific Force} = \frac{\mathrm{Force_{non-gravitational}}}{{\mathrm{Mass}}}</math>
+'''Specific force''' ('''SF''') is a [[Specific quantity|mass-specific quantity]] defined as the quotient of [[force]] per unit [[mass]].
-Specific force (also called [[g-force]] and mass-specific force) is measured in [[Metre per second squared|meters/second²]] (m·s<sup>-2</sup>) which is the units for acceleration. Thus, specific force is not actually a force, but a type of acceleration. However, the (mass-)specific force is not a coordinate-acceleration, but rather a [[proper acceleration]], which is the acceleration relative to free-fall. Forces, specific forces, and [[proper acceleration]]s are the same in all reference frames, but coordinate accelerations are frame-dependent. For free bodies, the specific force is the cause of, and a measure of, the body's [[proper acceleration]].
+:<math>\mathrm{SF} = F / m</math>
+It is a physical quantity of [[Kind of quantity|kind]] [[acceleration]], with [[Dimension (physics)|dimension]] of length per time squared and [[Unit of measurement|units]] of [[metre per second squared]] (m·s<sup>−2</sup>).
+It is normally applied to forces other than [[gravity]], to emulate the relationship between [[gravitational acceleration]] and [[gravitational force]].
-The [[g-force]] acceleration is the same as the specific force. The acceleration of an object free falling towards the earth depends on the reference frame (it disappears in the free-fall frame, also called the inertial frame), but any g-force "acceleration" will be present in all frames. This specific force is zero for freely-falling objects, since gravity acting alone does not produce g-forces or specific forces.
+It can also be called ''mass-specific weight'' (weight per unit mass), as the [[weight]] of an object is equal to the magnitude of the gravity force acting on it.
+The [[g-force]] is an instance of specific force measured in units of the [[standard gravity]] (''g'') instead of m/s², i.e., in multiples of ''g'' (e.g., "3 ''g''").
-Accelerometers on the surface of the Earth measure a constant 9.8 m/s^2 even when they are not accelerating (that is, when they do not undergo coordinate acceleration). This is because accelerometers measure the proper acceleration produced by the g-force exerted by the ground (gravity acting alone never produces g-force or specific force). Accelerometers measure specific force ([[proper acceleration]]), which is the acceleration relative to free-fall,<ref>www.strapdownassociates.com/Accels%20Measure.pdf</ref>, not the "standard" acceleration that is relative to a coordinate system.
+==Type of acceleration==
+The (mass-)specific force is not a [[coordinate acceleration]], but rather a [[proper acceleration]], which is the acceleration relative to free-fall. Forces, specific forces, and proper accelerations are the same in all reference frames, but coordinate accelerations are frame-dependent. For free bodies, the specific force is the cause of, and a measure of, the body's proper acceleration.
+The acceleration of an object free falling towards the earth depends on the reference frame (it disappears in the free-fall frame, also called the inertial frame), but any g-force "acceleration" will be present in all frames. This specific force is zero for freely-falling objects, since gravity acting alone does not produce g-forces or specific forces.
+[[Accelerometer]]s on the surface of the Earth measure a constant 9.8&nbsp;m/s^2 even when they are not accelerating (that is, when they do not undergo coordinate acceleration). This is because accelerometers measure the proper acceleration produced by the g-force exerted by the ground (gravity acting alone never produces g-force or specific force). Accelerometers measure specific force (proper acceleration), which is the acceleration relative to free-fall,<ref>{{Cite web|last=Savage|first=Paul G|date=May 8, 2005|title=What Do Accelerometers Measure?|url=http://www.strapdownassociates.com/Accels%20Measure.pdf|publisher=Strapdown Associates, Inc.}}</ref> not the "standard" acceleration that is relative to a coordinate system.
 ==Hydraulics==
 In open channel [[hydraulic engineering|hydraulics]], specific force (<math>F_s</math>) has a different meaning:
-:<math>F_s = \frac{y^2}{2} + \frac{q^2}{gy}</math>
+:<math>F_s = \frac{Q^2}{gA} + zA</math>
+where Q is the discharge, g is the acceleration due to gravity, A is the cross-sectional area of flow, and z is the depth of the centroid of flow area A.<ref>Chaudhry, M. Hanif "Open Channel Flow" 2nd Ed. (2008) pg.31 {{ISBN|978-0-387-30174-7}}</ref>
-where <math>q</math> is the discharge per unit width (<math>q = Q/B</math>) and <math>y</math> is the flow depth.
 ==See also==
@@ Line 24: / Line 34: @@
 [[Category:Physical quantities]]
 [[Category:Hydraulic engineering]]
+[[Category:Acceleration]]
-{{physics-stub}}
+{{classicalmechanics-stub}}
-[[ar:قوة نوعية]]