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{{Use dmy dates|date=September 2024}}
{{short description|Term for accelerations felt as weight in multiples of standard gravity}}
{{about|the physics concept||G-Force (disambiguation)}}
{{Redirect|G's|other uses|GS (disambiguation){{!}}GS}}
{{use dmy dates |date=September 2020}}
{{Lowercase title|G-Force}}
[[File:Load factor and the g-force in turn.svg|thumb|In straight and level flight, lift (''L'') equals weight (''W''). In a steady level banked turn of 60°, lift equals double the weight (''L''&nbsp;=&nbsp;2''W''). The pilot experiences 2&nbsp;''g'' and a doubled weight. The steeper the bank, the greater the g-forces.]]
[[File:Nitrolympics TopFuel 2005.jpg|thumb|This [[top fuel|top-fuel dragster]] can accelerate from zero to {{convert|160|km/h|0}} in 0.86 seconds. This is a horizontal acceleration of 5.3&nbsp;''g''. Combining this with the vertical g-force in the stationary case using the [[Pythagorean theorem]] yields a g-force of 5.4&nbsp;''g''.]]

The '''g-force''' or '''gravitational force equivalent''' is a [[Specific force|mass-specific force]] (force per unit mass), expressed in [[Unit of measurement|units]] of [[standard gravity]] (symbol ''g'' or ''g''<sub>0</sub>, not to be confused with "g", the symbol for [[grams]]).
It is used for sustained [[acceleration]]s that cause a perception of [[weight]]. For example, an object at rest on Earth's surface is subject to 1 ''g'', equaling the conventional value of [[gravitational acceleration]] on Earth, about {{val|9.8|ul=m/s2}}.<ref>{{cite web |last=Deziel |first=Chris |url=https://sciencing.com/convert-newtons-gforce-8720337.html |title=How to Convert Newtons to G-Force |website=sciencing.com |access-date=17 January 2021 |archive-date=29 January 2023 |archive-url=https://web.archive.org/web/20230129224605/https://sciencing.com/convert-newtons-gforce-8720337.html |url-status=live }}</ref>
More transient acceleration, accompanied with significant [[jerk (physics)|jerk]], is called [[Shock (mechanics)|''shock'']].{{fact|date=September 2024}}

When the g-force is produced by the surface of one object being pushed by the surface of another object, the reaction force to this push produces an equal and opposite force for every unit of each object's mass. The types of forces involved are transmitted through objects by interior [[Stress (mechanics)|mechanical stresses]]. [[Gravitational acceleration]] is one cause of an object's [[acceleration]] in relation to [[free fall]].<ref>[http://newton.dep.anl.gov/askasci/phy99/phy99491.htm G Force] {{Webarchive |url=https://web.archive.org/web/20120125033953/http://newton.dep.anl.gov/askasci/phy99/phy99491.htm |date=25 January 2012 }}. Newton.dep.anl.gov. Retrieved on 14 October 2011.</ref><ref>{{Cite book |url=https://books.google.com/books?id=zFl7y5xqHj4C&pg=PA6 |title=Principles of Medical Physiology |isbn=978-1-58890-572-7 |last=Sircar |first=Sabyasachi |date=12 December 2007 |publisher=Thieme |access-date=21 September 2020 |archive-date=21 July 2023 |archive-url=https://web.archive.org/web/20230721042220/https://books.google.com/books?id=zFl7y5xqHj4C&pg=PA6 |url-status=live }}</ref>

The g-force experienced by an object is due to the vector sum of all gravitational and non-gravitational forces acting on an object's freedom to move. In practice, as noted, these are surface-contact forces between objects. Such forces cause [[Stress (mechanics)|stresses]] and [[Strain (mechanics)|strains]] on objects, since they must be transmitted from an object surface. Because of these strains, large g-forces may be destructive.

For example, a force of 1&nbsp;''g'' on an object sitting on the Earth's surface is caused by the mechanical force exerted in the [[Ground reaction force|upward direction by the ground]], keeping the object from going into free fall. The upward contact force from the ground ensures that an object at rest on the Earth's surface is accelerating relative to the free-fall condition. (Free fall is the path that the object would follow when falling freely toward the Earth's center). Stress inside the object is ensured from the fact that the ground contact forces are transmitted only from the point of contact with the ground.

Objects allowed to free-fall in an ''inertial trajectory'', under the influence of gravitation only, feel no g-force – a condition known as [[weightlessness]]. Being in free fall in an inertial trajectory is colloquially called "zero-''g''", which is short for "zero g-force". Zero g-force conditions would occur inside an elevator falling freely toward the Earth's center (in vacuum), or [[Micro-g environment|(to good approximation) inside a spacecraft in Earth orbit]]. These are examples of coordinate acceleration (a change in velocity) without a sensation of weight.

In the absence of gravitational fields, or in directions at right angles to them, proper and coordinate accelerations are the same, and any coordinate acceleration must be produced by a corresponding g-force acceleration. An example of this is a rocket in free space: when the engines produce simple changes in velocity, those changes cause g-forces on the rocket and the passengers.

==Unit and measurement==

The [[unit of measure]] of [[acceleration]] in the [[International System of Units]] (SI) is m/s<sup>2</sup>.<ref>{{Cite journal |date=12 April 2010 |title=SI Units – Length |url=https://www.nist.gov/pml/owm/si-units-length |journal=NIST |language=en |access-date=18 December 2022 |archive-date=18 December 2022 |archive-url=https://web.archive.org/web/20221218153038/https://www.nist.gov/pml/owm/si-units-length |url-status=live }}</ref> However, to distinguish acceleration relative to free fall from simple acceleration (rate of change of velocity), the unit '''''g''''' is often used. One ''g'' is the force per unit mass due to gravity at the Earth's surface and is the [[standard gravity]] (symbol: ''g''<sub>n</sub>), defined as {{val|9.80665}}&nbsp;[[metre per second squared|metres per second squared]],<ref name="3rd CGPM">BIPM: [https://www.bipm.org/en/committees/cg/cgpm/3-1901/resolution-2 Declaration on the unit of mass and on the definition of weight; conventional value of g<sub>n</sub>] {{Webarchive|url=https://web.archive.org/web/20211016214949/https://www.bipm.org/en/committees/cg/cgpm/3-1901/resolution-2 |date=16 October 2021 }}.</ref> or equivalently {{val|9.80665}}&nbsp;[[newtons]] of force per kilogram of mass. The ''unit definition'' does not vary with location—the g-force when standing on the [[Moon]] is almost exactly {{frac|1|6}} that on Earth.
The unit ''g'' is not one of the SI units, which uses "g" for gram. Also, "''g''" should not be confused with "''G''", which is the standard symbol for the [[gravitational constant]].<ref name="symbols">Symbol g: ESA: GOCE, ''[http://www.esa.int/esaLP/ESAK4XZK0TC_LPgoce_0.html Basic Measurement Units] {{Webarchive|url=https://web.archive.org/web/20120212231429/http://www.esa.int/esaLP/ESAK4XZK0TC_LPgoce_0.html |date=February 12, 2012 }}'', NASA: ''[https://history.nasa.gov/SP-4201/ch2-4.htm Multiple G] {{Webarchive|url=https://web.archive.org/web/20171225233506/https://history.nasa.gov/SP-4201/ch2-4.htm |date=December 25, 2017 }}'', Astronautix: ''[http://www.astronautix.com/astros/stapp.htm Stapp] {{webarchive|url=https://web.archive.org/web/20090321182843/http://www.astronautix.com/astros/stapp.htm |date=March 21, 2009 }}'', Honeywell: ''[http://content.honeywell.com/sensing/sensotec/accelerometers.asp Accelerometers] {{webarchive|url=https://web.archive.org/web/20090217092615/http://content.honeywell.com/sensing/sensotec/accelerometers.asp |date=February 17, 2009 }}'', Sensr LLC: ''[http://www.sensr.com/products/gp1/index.php GP1 Programmable Accelerometer] {{webarchive|url=https://web.archive.org/web/20090201150824/http://sensr.com/products/gp1/index.php |date=February 1, 2009 }}'', Farnell: ''[http://au.farnell.com/jsp/search/browse.jsp?N=500001+1000197&Ntk=gensearch_001&Ntt=accelerometer&Ntx= accelometers]{{Dead link|date=February 2020 |bot=InternetArchiveBot |fix-attempted=yes }}'', Delphi: ''[http://delphi.com/about/motorsports/products/adr3/ Accident Data Recorder 3 (ADR3) MS0148] {{webarchive|url=https://web.archive.org/web/20081202091041/http://delphi.com/about/motorsports/products/adr3/ |date=December 2, 2008 }}'', NASA: ''[http://www.ksc.nasa.gov/facts/faq04.html Constants and Equations for Calculations] {{webarchive|url=https://web.archive.org/web/20090118161602/http://www.ksc.nasa.gov/facts/faq04.html |date=January 18, 2009 }}'', Jet Propulsion Laboratory: ''[http://mtp.jpl.nasa.gov/notes/altitude/altitude.html A Discussion of Various Measures of Altitude] {{webarchive|url=https://web.archive.org/web/20090210035728/http://mtp.jpl.nasa.gov/notes/altitude/altitude.html |date=February 10, 2009 }}'', National Highway Traffic Safety Administration: ''[http://www.nhtsa.dot.gov/cars/problems/studies/record/chidester.htm Recording Automotive Crash Event Data] {{Webarchive|url=https://web.archive.org/web/20100405091131/http://www.nhtsa.dot.gov/cars/problems/studies/record/chidester.htm |date=April 5, 2010 }}''<br />
Symbol G: Lyndon B. Johnson Space Center: [http://lsda.jsc.nasa.gov/books/apollo/s2ch5.htm ''ENVIRONMENTAL FACTORS: BIOMEDICAL RESULTS OF APOLLO'', Section II, Chapter 5] {{webarchive|url=https://web.archive.org/web/20081122024243/http://lsda.jsc.nasa.gov/books/apollo/s2ch5.htm |date=22 November 2008 }}, Honywell: ''[http://content.honeywell.com/sensing/sensotec/pdf_catalog08/008727-1-EN_Model_JTF_Gen_Pur.pdf Model JTF, General Purpose Accelerometer]'' </ref> This notation is commonly used in aviation, especially in aerobatic or combat military aviation, to describe the increased forces that must be overcome by pilots in order to remain conscious and not [[g-LOC]] (''g''-induced loss of consciousness).<ref>{{cite web |title=Pulling G's |url=http://goflightmedicine.com/pulling-gs/ |website=Go Flight Medicine |access-date=24 September 2014 |date=5 April 2013 |archive-date=12 January 2021 |archive-url=https://web.archive.org/web/20210112121657/https://goflightmedicine.com/pulling-gs/ |url-status=live }}</ref>

Measurement of g-force is typically achieved using an [[accelerometer]] (see discussion below in section [[#Measurement using an accelerometer]]). In certain cases, g-forces may be measured using suitably calibrated scales.

==Acceleration and forces==

{{unreferenced section|date=October 2022}}

The term g-"force" is technically incorrect as it is a measure of ''acceleration'', not force. While acceleration is a [[Euclidean vector|vector]] quantity, g-force accelerations ("g-forces" for short) are often expressed as a [[scalar (physics)|scalar]], based on the vector magnitude, with positive g-forces pointing downward (indicating upward acceleration), and negative g-forces pointing upward. Thus, a g-force is a vector of acceleration. It is an acceleration that must be produced by a mechanical force, and cannot be produced by simple gravitation. Objects acted upon ''only'' by gravitation experience (or "feel") no g-force, and are weightless.
g-forces, when multiplied by a mass upon which they act, are associated with a certain type of mechanical ''force'' in the correct sense of the term "force", and this force produces [[compressive stress]] and [[tensile stress]]. Such forces result in the operational sensation of weight, but the equation carries a sign change due to the definition of positive weight in the direction downward, so the direction of weight-force is opposite to the direction of g-force acceleration:

:Weight = mass × −g-force

The reason for the minus sign is that the actual ''force'' (i.e., measured weight) on an object produced by a g-force is in the opposite direction to the sign of the g-force, since in physics, weight is not the force that produces the acceleration, but rather the equal-and-opposite reaction force to it. If the direction upward is taken as positive (the normal cartesian convention) then ''positive'' g-force (an acceleration vector that points upward) produces a force/weight on any mass, that acts ''downward'' (an example is positive-g acceleration of a rocket launch, producing downward weight). In the same way, a ''negative-g force'' is an acceleration vector ''downward'' (the negative direction on the y axis), and this acceleration downward produces a weight-force in a direction ''upward'' (thus pulling a pilot upward out of the seat, and forcing blood toward the head of a normally oriented pilot).

If a g-force (acceleration) is vertically upward and is applied by the ground (which is accelerating through space-time) or applied by the floor of an elevator to a standing person, most of the body experiences compressive stress which at any height, if multiplied by the area, is the related mechanical force, which is the product of the g-force and the supported mass (the mass above the level of support, including arms hanging down from above that level). At the same time, the arms themselves experience a tensile stress, which at any height, if multiplied by the area, is again the related mechanical force, which is the product of the g-force and the mass hanging below the point of mechanical support. The mechanical resistive force spreads from points of contact with the floor or supporting structure, and gradually decreases toward zero at the unsupported ends (the top in the case of support from below, such as a seat or the floor, the bottom for a hanging part of the body or object). With compressive force counted as negative tensile force, the rate of change of the tensile force in the direction of the g-force, per unit mass (the change between parts of the object such that the slice of the object between them has unit mass), is equal to the g-force plus the non-gravitational external forces on the slice, if any (counted positive in the direction opposite to the g-force).

For a given g-force the stresses are the same, regardless of whether this g-force is caused by mechanical resistance to gravity, or by a coordinate-acceleration (change in velocity) caused by a mechanical force, or by a combination of these. Hence, for people all mechanical forces feels exactly the same whether they cause coordinate acceleration or not. For objects likewise, the question of whether they can withstand the mechanical g-force without damage is the same for any type of g-force. For example, upward acceleration (e.g., increase of speed when going up or decrease of speed when going down) on Earth feels the same as being stationary on a celestial body with a higher [[surface gravity]]. Gravitation acting alone does not produce any g-force; g-force is only produced from mechanical pushes and pulls. For a free body (one that is free to move in space) such g-forces only arise as the "inertial" path that is the natural effect of gravitation, or the natural effect of the inertia of mass, is modified. Such modification may only arise from influences other than gravitation.

Examples of important situations involving g-forces include:
* The g-force acting on a stationary object resting on the Earth's surface is 1&nbsp;''g'' (upwards) and results from the resisting reaction of the Earth's surface bearing upwards equal to an acceleration of 1&nbsp;''g'', and is equal and opposite to gravity. The number 1 is approximate, depending on location.
* The g-force acting on an object in any [[weightlessness|weightless]] environment such as free-fall in a vacuum is 0&nbsp;''g''.
* The g-force acting on an object under acceleration can be much greater than 1&nbsp;''g'', for example, the dragster pictured at top right can exert a horizontal g-force of 5.3 when accelerating.
* The g-force acting on an object under acceleration may be downwards, for example when cresting a sharp hill on a roller coaster.
* If there are no other external forces than gravity, the g-force in a [[rocket]] is the [[thrust]] per unit mass. Its magnitude is equal to the [[thrust-to-weight ratio]] times ''g'', and to the consumption of [[delta-v]] per unit time.
* In the case of a [[Shock (mechanics)|shock]], e.g., a [[collision]], the g-force can be very large during a short time.

A classic example of negative g-force is in a fully inverted [[roller coaster]] which is accelerating (changing velocity) toward the ground. In this case, the roller coaster riders are accelerated toward the ground faster than gravity would accelerate them, and are thus pinned upside down in their seats. In this case, the mechanical force exerted by the seat causes the g-force by altering the path of the passenger downward in a way that differs from gravitational acceleration. The difference in downward motion, now faster than gravity would provide, is caused by the push of the seat, and it results in a g-force toward the ground.

All "coordinate accelerations" (or lack of them), are described by [[Newton's laws of motion]] as follows:

The ''Second Law of Motion'', the law of acceleration, states that {{nowrap|''F'' {{=}} ''ma'',}} meaning that a force ''F'' acting on a body is equal to the [[mass]] ''m'' of the body times its acceleration ''a''.

The ''Third Law of Motion'', the law of reciprocal actions, states that all forces occur in pairs, and these two forces are equal in magnitude and opposite in direction. Newton's third law of motion means that not only does gravity behave as a force acting downwards on, say, a rock held in your hand but also that the rock exerts a force on the Earth, equal in magnitude and opposite in direction.
[[File:Red.bull.air.race.arp.750pix.jpg|thumb|right|This [[acrobatic airplane]] is pulling up in a +g maneuver; the pilot is experiencing several g's of inertial acceleration in addition to the force of gravity. The cumulative vertical axis forces acting upon his body make him momentarily 'weigh' many times more than normal.]]

In an airplane, the pilot's seat can be thought of as the hand holding the rock, the pilot as the rock. When flying straight and level at 1&nbsp;''g'', the pilot is acted upon by the force of gravity. His weight (a downward force) is {{convert|725|N|lk=on}}. In accordance with Newton's third law, the plane and the seat underneath the pilot provides an equal and opposite force pushing upwards with a force of 725&nbsp;N. This mechanical force provides the 1.0&nbsp;''g'' upward [[proper acceleration]] on the pilot, even though this velocity in the upward direction does not change (this is similar to the situation of a person standing on the ground, where the ground provides this force and this g-force).

If the pilot were suddenly to pull back on the stick and make his plane accelerate upwards at 9.8&nbsp;m/s<sup>2</sup>, the total g‑force on his body is 2&nbsp;''g'', half of which comes from the seat pushing the pilot to resist gravity, and half from the seat pushing the pilot to cause his upward acceleration—a change in velocity which also is a ''proper acceleration'' because it also differs from a free fall trajectory. Considered in the frame of reference of the plane his body is now generating a force of {{cvt|1450|N}} downwards into his seat and the seat is simultaneously pushing upwards with an equal force of 1450&nbsp;N.

Unopposed acceleration due to mechanical forces, and consequentially g-force, is experienced whenever anyone rides in a vehicle because it always causes a proper acceleration, and (in the absence of gravity) also always a coordinate acceleration (where velocity changes). Whenever the vehicle changes either direction or speed, the occupants feel lateral (side to side) or longitudinal (forward and backwards) forces produced by the mechanical push of their seats.

The expression {{nowrap|"1 ''g'' {{=}} {{val|9.80665|u=m/s<sup>2</sup>}}"}} means that ''for every second that elapses,'' velocity changes {{val|9.80665}} metres per second ({{val|35.30394|u=km/h}}). This rate of change in velocity can also be denoted as {{val|9.80665}} (metres per second) per second, or {{val|9.80665|u=m/s<sup>2</sup>.}} For example: An acceleration of 1&nbsp;''g'' equates to a rate of change in velocity of approximately {{cvt|35|km/h}} for each second that elapses. Therefore, if an automobile is capable of braking at 1&nbsp;''g'' and is traveling at 35&nbsp;km/h, it can brake to a standstill in one second and the driver will experience a deceleration of 1&nbsp;''g''. The automobile traveling at three times this speed, {{cvt|105|km/h}}, can brake to a standstill in three seconds.

In the case of an increase in speed from 0 to ''v'' with constant acceleration within a distance of ''s'' this acceleration is ''v''<sup>2</sup>/(2''s'').

Preparing an object for g-tolerance (not getting damaged when subjected to a high g-force) is called g-hardening.{{citation needed|date=February 2015}} This may apply to, e.g., instruments in a [[projectile]] shot by a gun.

==Human tolerance==
{{see also|Jerk (physics)#Physiological effects and human perception}}
[[File:Human linear acceleration tolerance.svg|thumb|250px|Semilog graph of the limits of tolerance of humans to linear acceleration<ref name=Brulle>{{cite book |title=Engineering the Space Age: A Rocket Scientist Remembers |author=Robert V. Brulle |page=135 |publisher=Air University Press |year=2008 |isbn=978-1-58566-184-8 |url=https://media.defense.gov/2017/Apr/05/2001727358/-1/-1/0/B_0113_BRULLE_ENGINEERING_SPACE_AGE.PDF |access-date=8 January 2020 |archive-url=https://web.archive.org/web/20170104164718/http://www.au.af.mil/au/aupress/digital/pdf/book/b_0113_brulle_engineering_space_age.pdf |archive-date=4 January 2017 }}</ref>]]

Human tolerances depend on the magnitude of the gravitational force, the length of time it is applied, the direction it acts, the location of application, and the posture of the body.<ref name=Balldin>{{cite book |last=Balldin |first=Ulf I. |editor-last=Lounsbury |editor-first=Dave E. |title=Medical conditions of Harsh Environments |volume=2 |chapter=Chapter 33: Acceleration effects on fighter pilots. |publisher=Office of The Surgeon General, Department of the Army, United States of America |place=Washington, DC |date=2002 |url=http://www.cs.amedd.army.mil/borden/Portlet.aspx?ID=7c0ebab2-6720-4e15-883b-dbfaafa960f9 |chapter-url=https://ke.army.mil/bordeninstitute/published_volumes/harshEnv2/HE2ch33.pdf |access-date=16 September 2013 |isbn=9780160510717 |oclc=49322507 |archive-date=6 August 2013 |archive-url=https://web.archive.org/web/20130806031016/http://www.cs.amedd.army.mil/borden/Portlet.aspx?ID=7c0ebab2-6720-4e15-883b-dbfaafa960f9 |url-status=dead }}</ref><ref name="BBB">George Bibel. ''Beyond the Black Box: the Forensics of Airplane Crashes''. Johns Hopkins University Press, 2008. {{ISBN|0-8018-8631-7}}.</ref>{{rp|350}}

The human body is flexible and deformable, particularly the softer tissues. A hard slap on the face may briefly impose hundreds of ''g'' locally but not produce any real damage; a constant 16&nbsp;''g'' for a minute, however, may be deadly. When [[vibration]] is experienced, relatively low peak g-force levels can be severely damaging if they are at the [[resonance|resonant frequency]] of organs or connective tissues.{{Citation needed|date=August 2021|reason=Where does 16g come from? Can we back up the claim about resonant frequency of body parts?}}

To some degree, g-tolerance can be trainable, and there is also considerable variation in innate ability between individuals. In addition, some illnesses, particularly [[Circulatory system|cardiovascular]] problems, reduce g-tolerance.

===Vertical===
Aircraft pilots (in particular) sustain g-forces along the axis aligned with the spine. This causes significant variation in blood pressure along the length of the subject's body, which limits the maximum g-forces that can be tolerated.

Positive, or "upward" g-force, drives blood downward to the feet of a seated or standing person (more naturally, the feet and body may be seen as being driven by the upward force of the floor and seat, upward around the blood). Resistance to positive g-force varies. A typical person can handle about {{cvt|5|g0|m/s2}} (meaning some people might pass out when riding a higher-g roller coaster, which in some cases exceeds this point) before [[G-LOC|losing consciousness]], but through the combination of special [[g-suit]]s and efforts to strain muscles—both of which act to force blood back into the brain—modern pilots can typically handle a sustained {{cvt|9|g0|m/s2}} (see [[High-G training]]).

In aircraft particularly, vertical g-forces are often positive (force blood towards the feet and away from the head); this causes problems with the eyes and brain in particular. As positive vertical g-force is progressively increased (such as in a [[centrifuge]]) the following symptoms may be experienced:{{Citation needed|date=January 2021}}
* [[Greyout (medical)|Grey-out]], where the vision loses hue, easily reversible on levelling out
* [[Tunnel vision]], where peripheral vision is progressively lost
* Blackout, a loss of vision while consciousness is maintained, caused by a lack of blood flow to the head
* [[G-LOC]], a g-force induced loss of consciousness<ref name="pmid3281645">{{cite journal |author=Burton RR |title=G-induced loss of consciousness: definition, history, current status |journal=Aviation, Space, and Environmental Medicine |volume=59 |issue=1 |pages=2–5 |date=1988 |pmid=3281645 }}</ref>
* Death, if g-forces are not quickly reduced

Resistance to "negative" or "downward" g, which drives blood to the head, is much lower. This limit is typically in the {{cvt|-2|to|-3|g0|m/s2}} range. This condition is sometimes referred to as [[red out]] where vision is literally reddened<ref>{{Cite book |url=https://books.google.com/books?id=hw_0x_pBP3AC&pg=PA60 |title=On the edge: Personal flying experiences during the Second World War |isbn=978-1-896182-87-2 |last1=Brown |first1=Robert G |date=1999 |publisher=GeneralStore PublishingHouse }}</ref> due to the blood-laden lower eyelid being pulled into the field of vision.<ref name="Fundamentals of Aerospace Medicine">{{cite book |last=DeHart |first=Roy L. |title=Fundamentals of Aerospace Medicine: 3rd Edition |date=2002 |publisher=Lippincott Williams & Wilkins }}</ref> Negative g-force is generally unpleasant and can cause damage. Blood vessels in the eyes or brain may swell or burst under the increased blood pressure, resulting in degraded sight or even blindness.

===Horizontal===
The human body is better at surviving g-forces that are perpendicular to the spine. In general when the acceleration is forwards (subject essentially lying on their back, colloquially known as "eyeballs in"),<ref>{{cite web |url=http://roland.lerc.nasa.gov/~dglover/dictionary//tables/table11.html |archive-url=https://web.archive.org/web/20080520061140/http://roland.lerc.nasa.gov/~dglover/dictionary//tables/table11.html |archive-date=20 May 2008 |title=NASA Physiological Acceleration Systems |date=20 May 2008 |url-status=dead |access-date=25 December 2012 }}</ref> a much higher tolerance is shown than when the acceleration is backwards (lying on their front, "eyeballs out") since blood vessels in the retina appear more sensitive in the latter direction.{{Citation needed|date=February 2013}}

Early experiments showed that untrained humans were able to tolerate a range of accelerations depending on the time of exposure. This ranged from as much as {{val|20|u=g0}} for less than 10 seconds, to {{val|10|u=g0}} for 1 minute, and {{val|6|u=g0}} for 10 minutes for both eyeballs in and out.<ref>[https://ntrs.nasa.gov/api/citations/19980223621/downloads/19980223621.pdf NASA Technical note D-337, Centrifuge Study of Pilot Tolerance to Acceleration and the Effects of Acceleration on Pilot Performance] {{Webarchive|url=https://web.archive.org/web/20220217014537/https://ntrs.nasa.gov/api/citations/19980223621/downloads/19980223621.pdf |date=17 February 2022 }}, by Brent Y. Creer, Captain Harald A. Smedal, USN (MC), and Rodney C. Wingrove, figure 10</ref> These forces were endured with cognitive facilities intact, as subjects were able to perform simple physical and communication tasks. The tests were determined not to cause long- or short-term harm although tolerance was quite subjective, with only the most motivated non-pilots capable of completing tests.<ref>[https://ntrs.nasa.gov/api/citations/19980223621/downloads/19980223621.pdf NASA Technical note D-337, Centrifuge Study of Pilot Tolerance to Acceleration and the Effects of Acceleration on Pilot Performance] {{Webarchive|url=https://web.archive.org/web/20220217014537/https://ntrs.nasa.gov/api/citations/19980223621/downloads/19980223621.pdf |date=17 February 2022 }}, by Brent Y. Creer, Captain Harald A. Smedal, USN (MC), and Rodney C. Vtlfngrove</ref> The record for peak experimental horizontal g-force tolerance is held by acceleration pioneer [[John Stapp]], in a series of rocket sled deceleration experiments culminating in a late 1954 test in which he was clocked in a little over a second from a land speed of Mach 0.9. He survived a peak "eyeballs-out" acceleration of 46.2 times the acceleration of gravity, and more than {{val|25|u=g0}} for 1.1 seconds, proving that the human body is capable of this. Stapp lived another 45 years to age 89<ref>[http://www.ejectionsite.com/stapp.htm Fastest Man on Earth – John Paul Stapp] {{Webarchive|url=https://web.archive.org/web/20171215201020/http://www.ejectionsite.com/stapp.htm |date=15 December 2017 }}. Ejection Site. Retrieved on 14 October 2011.</ref> without any ill effects.<ref>{{cite web |last1=Martin |first1=Douglas |title=John Paul Stapp, 89, Is Dead; 'The Fastest Man on Earth' |url=https://www.nytimes.com/1999/11/16/us/john-paul-stapp-89-is-dead-the-fastest-man-on-earth.html |website=The New York Times |access-date=29 October 2016 |date=16 November 1999 |archive-date=3 September 2023 |archive-url=https://web.archive.org/web/20230903155450/https://www.nytimes.com/1999/11/16/us/john-paul-stapp-89-is-dead-the-fastest-man-on-earth.html |url-status=live }}</ref>

The highest recorded g-force experienced by a human who survived was during the [[2003 IndyCar Series]] finale at Texas Motor Speedway on 12 October 2003, in the 2003 Chevy 500 when the car driven by [[Kenny Bräck]] made wheel-to-wheel contact with [[Tomas Scheckter]]'s car. This immediately resulted in Bräck's car impacting the catch fence that would record a peak of {{val|214|u=g0}}.<ref>{{cite web |url=http://www.news.com.au/sport/motorsport/formula-one/jules-bianchi-survived-92g-impact-in-horror-formula-one-crash/news-story/c381589f42393105511f8413c3b2fd52 |title=New details from horror crash |website=News.com.au |access-date=30 December 2017 |date=16 October 2014 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201032013/http://www.news.com.au/sport/motorsport/formula-one/jules-bianchi-survived-92g-impact-in-horror-formula-one-crash/news-story/c381589f42393105511f8413c3b2fd52 |url-status=live }}</ref><ref>{{cite web |url=http://www.crash.net/indycar/news/20962/1/qa-kenny-brack.html |title=Q&A: Kenny Brack |date=13 October 2004 |website=Crash.net |access-date=30 December 2017 }}</ref>

==Short duration shock, impact, and jerk==
[[impact (mechanics)|Impact]] and [[mechanical shock]] are usually used to describe a high-[[kinetic energy|kinetic-energy]], short-term excitation. A shock pulse is often measured by its peak acceleration in {{math|''ɡ''<sub>0</sub>}}·s and the pulse duration. [[Vibration]] is a periodic [[oscillation]] which can also be measured in {{math|''ɡ''<sub>0</sub>}}·s as well as frequency. The dynamics of these phenomena are what distinguish them from the g-forces caused by a relatively longer-term accelerations.{{fact|date=September 2024}}

After a free fall from a height <math>h</math> followed by deceleration over a distance <math>d</math> during an impact, the shock on an object is <math>(h/d)</math>·&nbsp;{{math|''ɡ''<sub>0</sub>}}. For example, a stiff and compact object dropped from 1&nbsp;m that impacts over a distance of 1&nbsp;mm is subjected to a 1000 {{math|''ɡ''<sub>0</sub>}} deceleration.{{fact|date=September 2024}}

[[Jerk (physics)|Jerk]] is the rate of change of acceleration. In SI units, jerk is expressed as m/s<sup>3</sup>; it can also be expressed in [[standard gravity]] per second ({{math|''ɡ''<sub>0</sub>}}/s; 1 {{math|''ɡ''<sub>0</sub>}}/s ≈ 9.81&nbsp;m/s<sup>3</sup>).{{fact|date=September 2024}}

==Other biological responses==
Recent research carried out on [[extremophile]]s in Japan involved a variety of bacteria (including ''[[E. coli]]'' as a non-extremophile control) being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an [[ultracentrifuge]] at high speeds corresponding to 403,627 g. ''[[Paracoccus denitrificans]]'' was one of the bacteria that displayed not only survival but also robust cellular growth under these conditions of hyperacceleration, which are usually only to be found in cosmic environments, such as on very massive stars or in the shock waves of [[supernova]]s. Analysis showed that the small size of prokaryotic cells is essential for successful growth under [[hypergravity]]. Notably, two multicellular species, the [[nematode]]s ''[[Panagrolaimus superbus]]''<ref>{{cite journal |last1=de Souza |first1=T.A.J. |display-authors=etal |year=2017 |title=Survival potential of the anhydrobiotic nematode ''Panagrolaimus superbus'' submitted to extreme abiotic stresses. ISJ-Invertebrate Survival Journal |journal=Invertebrate Survival Journal |volume=14 |issue=1 |pages=85–93 |doi=10.25431/1824-307X/isj.v14i1.85-93 }}</ref> and ''Caenorhabditis elegans'' were shown to be able to tolerate 400,000 × ''g'' for 1 hour.<ref>{{cite journal |last1=de Souza |first1=T.A.J. |display-authors=etal |year=2018 |title=''Caenorhabditis elegans'' Tolerates Hyperaccelerations up to 400,000 x g. Astrobiology |journal=Astrobiology |volume=18 |issue=7 |pages=825–833 |doi=10.1089/ast.2017.1802 |pmid=29746159 |s2cid=13679378 }}</ref>
The research has implications on the feasibility of [[panspermia]].<ref>{{cite web |url=http://news.nationalgeographic.com/news/2011/04/110425-gravity-extreme-bacteria-e-coli-alien-life-space-science/ |archive-url=https://web.archive.org/web/20110427083206/http://news.nationalgeographic.com/news/2011/04/110425-gravity-extreme-bacteria-e-coli-alien-life-space-science/ |url-status=dead |archive-date=27 April 2011 |title=Bacteria Grow Under 400,000 Times Earth's Gravity |author=Than, Ker |date=25 April 2011 |website=National Geographic- Daily News |publisher=National Geographic Society |access-date=28 April 2011 }}</ref><ref>{{cite journal |last1=Deguchi |first1=Shigeru |author2=Hirokazu Shimoshige |author3=Mikiko Tsudome |author4=Sada-atsu Mukai |author5=Robert W. Corkery |author6=Susumu Ito |author7=Koki Horikoshi |date=2011 |title=Microbial growth at hyperaccelerations up to 403,627 × ''g'' |journal=Proceedings of the National Academy of Sciences |volume=108 |issue=19 |pages=7997–8002 |doi=10.1073/pnas.1018027108 |pmid=21518884 |bibcode=2011PNAS..108.7997D |pmc=3093466 |doi-access=free }}</ref>

==Typical examples==
{{main|Orders of magnitude (acceleration)}}
{| class="wikitable sortable"
|-
!Example
!g-force{{efn|Including contribution from resistance to gravity.}}
|-
|The gyro rotors in [[Gravity Probe B]] and the free-floating proof masses in the TRIAD I navigation satellite<ref>Stanford University: ''[http://einstein.stanford.edu/TECH/technology2.html Gravity Probe B, Payload & Spacecraft] {{Webarchive|url=https://web.archive.org/web/20141013051627/http://einstein.stanford.edu/TECH/technology2.html |date=October 13, 2014 }}'', and NASA: ''[https://web.archive.org/web/20041018112953/http://esto.nasa.gov/files/2002/Drag-Free%20Technology/DFC_ESTO_final_97.pdf Investigation of Drag-Free Control Technology for Earth Science Constellation Missions]''. The TRIAD 1 satellite was a later, more advanced navigation satellite that was part of the U.S. Navy's [[Transit (satellite)|Transit]], or NAVSAT system.</ref>
|align="right"|0&nbsp;''g''
|-
|A ride in the [[Vomit Comet]] (parabolic flight)
|align="right"|[[Approximation#Unicode|≈]] 0&nbsp;''g''
|-
|Standing on [[Mimas (moon)|Mimas]], the smallest and least massive known body [[hydrostatic equilibrium#Planetary geology|rounded by its own gravity]]
|align="right"|0.006&nbsp;''g''
|-
|Standing on [[Ceres (dwarf planet)|Ceres]], the smallest and least massive known body ''currently'' in [[hydrostatic equilibrium#Planetary geology|hydrostatic equilibrium]]
|align="right"|0.029&nbsp;''g''
|-
|Standing on [[Pluto]] at average ground level
|align="right"|0.063&nbsp;''g''
|-
|Standing on [[Eris (dwarf planet)|Eris]] at average ground level
|align="right"|0.084&nbsp;''g''
|-
|Standing on [[Titan (moon)|Titan]] at average ground level
|align="right"|0.138&nbsp;''g''
|-
|Standing on [[Ganymede (moon)|Ganymede]] at average surface level
|align="right"|0.146&nbsp;''g''
|-
|Standing on the [[Moon]] at surface level
|align="right"|0.1657&nbsp;''g''
|-
|2000 [[Toyota Sienna]] from 0 to 100&nbsp;km/h in 9.2&nbsp;s<ref>{{Cite web |url=https://autofiles.com/0-60-times/toyota/sienna/#2000 |title=Toyota Sienna 0–60 Times and Quarter Mile |website=autofiles.com |access-date=11 September 2023 |archive-date=2 November 2023 |archive-url=https://web.archive.org/web/20231102163021/https://autofiles.com/0-60-times/toyota/sienna/#2000 |url-status=live }}</ref>
|align="right"|0.3075–0.314&nbsp;''g''
|-
|Standing on [[Mercury (planet)|Mercury]] 
|align="right"|0.377&nbsp;''g''
|-
|Standing on [[Mars]] at its equator at mean ground level
|align="right"|0.378&nbsp;''g''
|-
|Standing on [[Venus]] at average ground level
|align="right"|0.905&nbsp;''g''
|-
|Standing on Earth at sea level–standard
|align="right"|1&nbsp;''g''
|-
|[[Saturn V]] Moon rocket just after launch and the gravity of [[Neptune]] where atmospheric pressure is about Earth's
|align="right"|1.14&nbsp;''g''
|-
|[[Bugatti Veyron]] from 0 to 100&nbsp;km/h in 2.4&nbsp;s
|align="right"|1.55&nbsp;''g''{{efn|Directed 40 degrees from horizontal.}}
|-
|[[Gravitron]] amusement ride
|align="right"|2.5–3&nbsp;''g''
|-
|Gravity of [[Jupiter]] at its mid-latitudes and where atmospheric pressure is about Earth's
|align="right"|2.528&nbsp;''g''
|-
|Uninhibited sneeze after sniffing ground pepper<ref name="allen94">{{cite journal |author=Allen M.E. |author2=Weir-Jones I |display-authors=etal |year=1994 |journal=[[Spine (journal)|Spine]] |volume=19 |issue=11 |pages=1285–1290 |title=Acceleration perturbations of daily living. A comparison to 'whiplash' |pmid=8073323 |doi=10.1097/00007632-199405310-00017 |s2cid=41569450 }}</ref>
|align="right"|2.9 ''g''
|-
|[[Space Shuttle]], maximum during launch and reentry
|align="right"|3&nbsp;''g''
|-
|High-g [[roller coaster]]s<ref name="BBB"/>{{rp|340}}
|align="right"|3.5–12&nbsp;''g''
|-
|Hearty greeting slap on upper back<ref name="allen94"/>
|align="right"|4.1 ''g''
|-
|[[Top Fuel]] [[drag racing]] world record of 4.4&nbsp;s over 1/4 mile
| align="right" |4.2&nbsp;''g''
|-
|First world war aircraft (ex:[[Sopwith Camel]], [[Fokker Dr.1]], [[SPAD S.XIII]], [[Nieuport 17]], [[Albatros D.III]]) in dogfight maneuvering.
| align="right" |4.5–7&nbsp;''g''
|-
|[[Luge]], maximum expected at the Whistler Sliding Centre
|align="right"|5.2&nbsp;''g''
|-
|[[Formula One car]], maximum under heavy braking<ref>{{cite web |url=https://www.youtube.com/watch?v=zJRh9FG83d0 |archive-url=https://ghostarchive.org/varchive/youtube/20211030/zJRh9FG83d0 |archive-date=30 October 2021 |title=F1 2017 v 2016: G-Force Comparison |last=FORMULA 1 |date=31 March 2017 |access-date=30 December 2017 |publisher=YouTube}}{{cbignore }}</ref>
|align="right"|6.3&nbsp;''g''
|-
|[[Gold Reef City#Rides and attractions|Tower Of Terror]], highest g-force steel rollercoaster
|align="right"|6.3&nbsp;''g''
|-
|[[Formula One car]], peak lateral in turns<ref>6&nbsp;''g'' has been recorded in the 130R turn at Suzuka circuit, Japan. ''{{cite web |url=http://www.formula1.com/news/headlines/2009/9/10005.html |title=Formula 1™{{dash}}the Official F1™ Website |access-date=October 12, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20100228061655/http://www.formula1.com/news/headlines/2009/9/10005.html |archive-date=February 28, 2010}}'' Many turns have 5&nbsp;''g'' peak values, like turn 8 at Istanbul or Eau Rouge at Spa</ref>
|align="right"|6–6.5&nbsp;''g''
|-
|Standard, full aerobatics certified [[Glider aircraft|glider]]
|align="right"|+7/−5&nbsp;''g''
|-
|[[Apollo 16]] on reentry<ref>NASA: [https://web.archive.org/web/20090226122959/http://lsda.jsc.nasa.gov/books/apollo/Resize-jpg/ts2c5-2.jpg Table 2: Apollo Manned Space Flight Reentry G Levels] Lsda.jsc.nasa.gov</ref>
|align="right"|7.19&nbsp;''g''
|-
|Maximum permitted g-force in [[Sukhoi Su-27]] plane
|align="right"|9&nbsp;''g''
|-
|Maximum permitted g-force in [[Mikoyan MiG-35]] plane and maximum permitted g-force turn in [[Red Bull Air Race]] planes
|align="right"|10&nbsp;''g''
|-
|[[Flip Flap Railway]], highest g-force wooden rollercoaster
|align="right"|12&nbsp;''g''
|-
|Jet Fighter pilot during [[ejection seat]] activation
|align="right"|15–25&nbsp;''g''
|-
|Gravitational acceleration at the surface of the [[Sun]]
|align="right"|28&nbsp;''g''
|-
|Maximum g-force in [[Tor missile system]]<ref>"Russia trains Greek Tor-M1 crews". RIA Novosti. 27 December 2007. Retrieved 2008-09-04.</ref> 
|align="right"|30&nbsp;''g''
|-
|[[John Stapp#Work on effects of deceleration|Maximum for human on a rocket sled]]
|align="right"|46.2&nbsp;''g''
|-
|[[Formula One]] [[2021 British Grand Prix]] [[Max Verstappen]] Crash with [[Lewis Hamilton]]
|align="right"|51&nbsp;''g''
|-
|[[Formula One]] [[2020 Bahrain Grand Prix]] [[Romain Grosjean]] Crash<ref>{{cite web |url=https://www.fia.com/news/fia-concludes-investigation-romain-grosjeans-accident-2020-bahrain-formula-1-grand-prix-and |title=FIA CONCLUDES INVESTIGATION INTO ROMAIN GROSJEAN'S ACCIDENT AT 2020 BAHRAIN FORMULA 1 GRAND PRIX AND RELEASES 2021 CIRCUIT RACING SAFETY INITIATIVES |website=www.fia.com |date=5 March 2021 |access-date=20 July 2021 |archive-date=4 April 2023 |archive-url=https://web.archive.org/web/20230404155008/https://www.fia.com/news/fia-concludes-investigation-romain-grosjeans-accident-2020-bahrain-formula-1-grand-prix-and |url-status=live }}</ref>
|align="right"|67&nbsp;''g''
|-
|[[Sprint (missile)|Sprint missile]]
|align="right"|100&nbsp;''g''
|-
|Brief human exposure survived in crash<ref name="nhtsa.dot.gov">"Several Indy car drivers have withstood impacts in excess of 100 G without serious injuries." Dennis F. Shanahan, M.D., M.P.H.: [http://ftp.rta.nato.int/public/PubFullText/RTO/EN/RTO-EN-HFM-113/EN-HFM-113-06.pdf ''Human Tolerance and Crash Survivability''] {{Webarchive |url=https://web.archive.org/web/20131104162124/http://ftp.rta.nato.int/public//PubFullText/RTO/EN/RTO-EN-HFM-113///EN-HFM-113-06.pdf |date=4 November 2013 }}, citing Society of Automotive Engineers. Indy racecar crash analysis. Automotive Engineering International, June 1999, 87–90. And National Highway Traffic Safety Administration: ''[http://www.nhtsa.dot.gov/cars/problems/studies/record/chidester.htm Recording Automotive Crash Event Data] {{Webarchive |url=https://web.archive.org/web/20100405091131/http://www.nhtsa.dot.gov/cars/problems/studies/record/chidester.htm |date=5 April 2010 }}''</ref>
|align="right"|> 100&nbsp;''g''
|-
|[[IndyCar]] [[2003 Chevy 500|2003 Texas]] [[Kenny Bräck]] Crash
|align="right"|214&nbsp;''g''
|-
||[[Formula One]] [[2014 Japanese Grand Prix]] [[Jules Bianchi]] Crash 
|align="right"|254 ''g''
|-
|[[Formula One]] [[1994 Monaco Grand Prix]] [[Karl Wendlinger]]<ref>Mellor, Andrew. "Formula One Accident Investigations." SAE Technical Paper 2000-01-3552 (2000). https://doi.org/10.4271/2000-01-3552.
</ref> Crash
|align="right"|≈360&nbsp;''g''
|-
|[[Coronal mass ejection]] (Sun)<ref>{{cite journal |author=Fang Shen, S. T. Wu, Xueshang Feng, Chin-Chun Wu |year=2012 |journal=Journal of Geophysical Research: Space Physics |volume=117 |issue=A11 |title=Acceleration and deceleration of coronal mass ejections during propagation and interaction |pages= |doi=10.1029/2012JA017776 |bibcode=2012JGRA..11711101S |doi-access=free }}</ref>
|align="right"|480 ''g''
|-
|[[Formula One]] [[1994 San Marino Grand Prix]] [[Roland Ratzenberger]] Qualifying Crash 
|align="right"|500 ''g''
|-
|[[Space gun]] with a barrel length of 1&nbsp;km and a [[muzzle velocity]] of 6&nbsp;km/s, as proposed by [[Quicklaunch]] (assuming constant acceleration)
|align="right"|1,800 ''g''
|-
|Shock capability of mechanical wrist watches<ref>{{cite web |url=http://www.omegawatches.com/customer-service/faq |title=OMEGA Watches: FAQ |date=10 February 2010 |access-date=30 December 2017 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20100210023046/http://www.omegawatches.com/customer-service/faq#faq-5 |archive-date=10 February 2010 }}</ref>
|align="right"|> 5,000 ''g''
|-
|V8 [[Formula One engine]], maximum piston acceleration<ref>{{cite web |url=http://www.auto123.com/en/racing-news/formula-1/f1-stunning-data-about-the-cosworth-v-8-formula-1-engine?artid=117234 |title=F1: Stunning data about the Cosworth V-8 Formula 1 engine{{dash}}Auto123.com |website=Auto123.com |access-date=30 December 2017 |archive-date=5 January 2015 |archive-url=https://web.archive.org/web/20150105113309/http://www.auto123.com/en/racing-news/formula-1/f1-stunning-data-about-the-cosworth-v-8-formula-1-engine?artid=117234 |url-status=live }}</ref>
|align="right"|8,600 ''g''
|-
|[[Mantis Shrimp]], acceleration of claw during predatory strike<ref>{{cite journal |author=S. N. Patek, W. L. Korff & R. L. Caldwell |year=2004 |journal=[[Nature (journal)|Nature]] |volume=428 |pages=819–820 |title=Deadly strike mechanism of a mantis shrimp |doi=10.1038/428819a |pmid=15103366 |issue=6985 |bibcode=2004Natur.428..819P |s2cid=4324997 |url=https://pateklab.biology.duke.edu/sites/pateklab.biology.duke.edu/files/Pateketal2004Nature.pdf |access-date=13 June 2018 |archive-date=26 January 2021 |archive-url=https://web.archive.org/web/20210126130108/https://pateklab.biology.duke.edu/sites/pateklab.biology.duke.edu/files/Pateketal2004Nature.pdf |url-status=dead }}</ref>
|align="right"|10,400 ''g''
|-
|Rating of electronics built into military artillery shells<ref>{{cite web |url=http://www.iechome.com/news/032003.htm |title=L3 IEC |website=Iechome.com |access-date=30 December 2017 |archive-url=https://web.archive.org/web/20110221062358/http://www.iechome.com/news/032003.htm |archive-date=21 February 2011 |url-status=dead }}</ref>
|align="right"|15,500 ''g''
|-
|Analytical ultracentrifuge spinning at 60,000&nbsp;rpm, at the bottom of the analysis cell (7.2&nbsp;cm)<ref>(rpm·π/30)<sup>2</sup>·0.072/g</ref>
|align="right"|300,000&nbsp;''g''
|-
|Calculated acceleration of the mandibles of the ant species ''[[Mystrium|Mystrium camillae]]''<ref>{{cite web |last1=Bittel |first1=Jason |title=Dracula ant's killer bite makes it the fastest animal on Earth |url=https://www.nationalgeographic.com/animals/article/dracula-ant-fastest-animal-quickest-strike-on-record |archive-url=https://web.archive.org/web/20210306180237/https://www.nationalgeographic.com/animals/article/dracula-ant-fastest-animal-quickest-strike-on-record |url-status=dead |archive-date=6 March 2021 |website=National Geographic |access-date=5 November 2023 }}</ref>
|align="right"|607,805&nbsp;''g''
|-
|Acceleration of a [[Cnidocyte|nematocyst]]: the fastest recorded acceleration from any biological entity.<ref name="Timm+2006">{{cite journal |author=Nüchter Timm |author2=Benoit Martin |author3=Engel Ulrike |author4=Özbek Suat |author5=Holstein Thomas W |title=Nanosecond-scale kinetics of nematocyst discharge |journal=Current Biology |volume=16 |issue=9 |pages=R316–R318 |year=2006 |doi=10.1016/j.cub.2006.03.089 |pmid=16682335 |doi-access=free |bibcode=2006CBio...16.R316N }}</ref>
|align="right"|5,410,000&nbsp;''g''
|-
|Mean acceleration of a proton in the [[Large Hadron Collider]]<ref>(7&nbsp;TeV/(20 minutes·c))/proton mass</ref>
|align="right"|190,000,000&nbsp;''g''
|-
|Gravitational acceleration at the surface of a typical [[neutron star]]<ref>{{cite book |title=An Introduction to the Sun and Stars |edition=illustrated |first1=Simon F. |last1=Green |first2=Mark H. |last2=Jones |first3=S. Jocelyn |last3=Burnell |publisher=Cambridge University Press |year=2004 |isbn=978-0-521-54622-5 |page=322 |url=https://books.google.com/books?id=lb5owLGIQGsC}} [https://books.google.com/books?id=lb5owLGIQGsC&pg=PA322 Extract of page 322] note: {{val|2.00|e=12|u=ms<sup>−2</sup>}} = {{val|2.04|e=11|u=g }}</ref>
|align="right"|{{val|2.0|e=11|u=''g''}}
|-
|Acceleration from a [[wakefield plasma accelerator]]<ref>(42&nbsp;''g''eV/85&nbsp;cm)/electron mass</ref>
|align="right"|{{val|8.9|e=20|u=''g''}}
|}

==Measurement using an accelerometer==
{{Unreferenced section|date=October 2022}}
[[File:Superman Escape from Krypton tower.jpg|thumb|right|upright|The [[Superman: Escape from Krypton]] roller coaster at [[Six Flags Magic Mountain]] provides 6.5 seconds of ballistic weightlessness.]]

An [[accelerometer]], in its simplest form, is a [[dashpot|damped]] mass on the end of a spring, with some way of measuring how far the mass has moved on the spring in a particular direction, called an 'axis'.

Accelerometers are often [[calibrate]]d to measure g-force along one or more axes. If a stationary, single-axis accelerometer is oriented so that its measuring axis is horizontal, its output will be 0&nbsp;''g'', and it will continue to be 0&nbsp;''g'' if mounted in an automobile traveling at a constant velocity on a level road. When the driver presses on the brake or gas pedal, the accelerometer will register positive or negative acceleration.

If the accelerometer is rotated by 90° so that it is vertical, it will read +1&nbsp;''g'' upwards even though stationary. In that situation, the accelerometer is subject to two forces: the [[gravitational force]] and the [[ground reaction force]] of the surface it is resting on. Only the latter force can be measured by the accelerometer, due to mechanical interaction between the accelerometer and the ground. The reading is the acceleration the instrument would have if it were exclusively subject to that force.

A three-axis accelerometer will output zero‑g on all three axes if it is dropped or otherwise put into a [[Ballistics|ballistic]] trajectory (also known as an [[inertial]] trajectory), so that it experiences "free fall", as do astronauts in orbit (astronauts experience small tidal accelerations called microgravity, which are neglected for the sake of discussion here). Some amusement park rides can provide several seconds at near-zero g. Riding NASA's "[[Vomit Comet]]" provides near-zero g-force for about 25 seconds at a time.

==See also==
* [[Artificial gravity]]
* [[Earth's gravity]]
* [[Gravitational acceleration]]
* [[Gravitational interaction]]
* [[Hypergravity]]
* [[Load factor (aeronautics)]]
* [[Peak ground acceleration]] – g-force of earthquakes
* [[Prone pilot]]
* [[Apparent weight#Comparison with g-force|Relation between g-force and apparent weight]]
* [[Shock and vibration data logger]]
* [[Shock detector]]
* [[Supine cockpit]]

==Notes and references==
{{notelist}}
{{Reflist}}

==Further reading==
* {{cite journal |last=Faller |first=James E. |title=The Measurement of Little g: A Fertile Ground for Precision Measurement Science |journal=Journal of Research of the National Institute of Standards and Technology |volume=110 |issue=6 |pages=559–581 |date=November–December 2005 |doi=10.6028/jres.110.082 |pmid=27308179 |pmc=4846227}}

==External links==
* [https://books.google.com/books?id=PyEDAAAAMBAJ&pg=PA91 "How Many Gs Can a Flyer Take?"], October 1944, ''[[Popular Science]]''—one of the first detailed public articles explaining this subject
* [https://www.wired.com/wired/archive/11.03/7g.html Enduring a human centrifuge at the NASA Ames Research Center] at ''[[Wired (magazine)|Wired]]''
* [https://aviation.stackexchange.com/questions/6411/does-a-prone-position-for-the-pilot-minimize-g-force-effects]
* [https://www.nestofdragons.net/weird-airplanes/proned-pilots/]
* [https://www.nurflugel.com/Nurflugel/n_o_d/weird_07.htm]
* [https://medium.com/@vaishnavirajesh/a-preface-to-planes-with-pronated-pilots-33f5286cd721]
* [https://apps.dtic.mil/sti/tr/pdf/AD0282780.pdf HUMAN CAPABILITIES IN THE PRONE AND SUPINE POSITIONS. AN ANNOTATED BIBLIOGRAPHY]

{{DEFAULTSORT:G-Force}}
[[Category:Acceleration]]
[[Category:Gravimetry]]
[[Category:Units of acceleration]]