g-force (also G-force, g-load) is a measurement of an object's acceleration expressed in gs. It may also informally refer to the reaction force resulting from an acceleration, with the causing acceleration expressed in gs. In Physics, a force is whatever can cause an object with Mass to Accelerate. The g (pronounced /ˈdʒiː/) is a non-SI unit equal to the nominal acceleration due to gravity on Earth at sea level, defined as 9. 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 (32. 174 ft/s²). More precisely, g-force measures the net effect of the acceleration that an object actually experiences and the acceleration that gravity is trying to impart to it, as explained further below. Gravitation is a natural Phenomenon by which objects with Mass attract one another The symbol g is properly written in lowercase and italic, to distinguish it from the symbol G, the gravitational constant, which is always written in uppercase; and from g, the symbol for gram, which is not italicised. The gravitational constant, denoted G, is a Physical constant involved in the calculation of the gravitational attraction between objects with mass For other uses of the words gram or gramme see Gram (disambiguation.

Connection with force

Although actually a measurement of acceleration, the term g-force is, as its name implies, popularly imagined to refer to the force that an accelerating object "feels". In Physics, a force is whatever can cause an object with Mass to Accelerate. These so-called "g-forces" are experienced, for example, by fighter jet pilots or riders on a roller coaster, and are caused by changes in speed and direction. The roller coaster is a popular Amusement ride developed for Amusement parks and modern Theme parks LaMarcus Adna Thompson patented the first For example, on a roller coaster high positive g-forces are experienced when the car's path curves upwards, where riders feel as if they weigh more than usual. This is often reversed when the car's path curves downwards, and lower than normal g-forces are felt, causing the riders to feel lighter or even weightless.

The relationship between force and acceleration stems from Newton's second law, F = ma, where F is force, m is mass and a is acceleration. Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the This equation shows that the larger an object's mass, the larger the force it experiences under the same acceleration. Thus, objects with different masses experiencing numerically identical "g-forces" will in fact be subject to forces of quite different magnitude. For this reason, g-force cannot be considered to measure force in absolute terms. However, the interpretation of g-force as a force can be partially rescued by noting that its numerical value is the ratio of the force "felt" by an object under the given acceleration to the force that the same object "feels" when resting stationary on the Earth's surface. For example, a person experiencing a g-force of 3 g feels three times as heavy as normal.

Because of the potential for confusion about whether g-force measures acceleration or force, the term is considered by some to be a misnomer. Scientific usage prefers explicit reference to either acceleration or force, and use of the appropriate units (in the SI system, metres per second squared for acceleration, and newtons for force). The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical

Calculating g-forces

While accelerations are often calculated relative to the Earth, g-force measures an object's acceleration in an inertial reference frame. In Physics, an inertial frame of reference is a Frame of reference which belongs to a set of frames in which Physical laws hold in the same and simplest Thus, if one is given an object's acceleration relative to the Earth, one must subtract off the acceleration of the Earth's reference frame relative to free-fall. The latter amount is, in most cases, approximately 1 g.

As acceleration is a vector quantity, this subtraction must be vector subtraction. However, if all the accelerations are in parallel directions, one can substitute scalar subtraction. Thus, in a simplified scenario where accelerations are assumed to act only upwards (positive) or downwards (negative), calculating g-force simply amounts to subtracting the acceleration (relative to the Earth) due to Earth's gravity (1 g in the downwards direction) from the object's acceleration relative to Earth. Since we are taking downward acceleration as negative, this is equivalent to adding 1 g. So, for example:

• An object at rest with respect to the Earth experiences a g-force of 0 g + 1 g, or just 1 g ("normal weight").

• An object in free fall (accelerating downwards at 1 g relative to the Earth) experiences a g-force of −1 g + 1 g = 0 g ("weightless")

• An object accelerating upwards at 1 g relative to the Earth experiences a g-force of 1 g + 1 g = 2 g ("twice normal weight")

• An object accelerating downwards at 2 g relative to the Earth experiences a g-force of −2 g + 1 g = −1 g ("negative g").

More generally, an object's acceleration may act in any direction (not just vertically), so in a fuller treatment the vector calculation must be used.

In cases when the magnitude of the acceleration is relatively large compared to 1 g, and/or is more-or-less horizontal, the effect of the Earth's gravity is sometimes ignored in everyday treatments. For example, if a person in a car accident decelerates from 30 m/s to rest in 0. 2 seconds, then their deceleration is 150 m/s², so one might say that they experience a g-force of about 150/9. 8 g, or about 15. 3 g. Strictly speaking, due to the vector addition of the gravitational acceleration, the true g-force has a slightly larger magnitude and is pointing slightly downwards (intuitively this is because the person is already experiencing 1 g just by sitting in the car).

The g-force experienced when cornering can be calculated from the radial acceleration formula, a = v²/r, where a is acceleration, v is velocity and r is the corner's radius of curvature. In Physics, velocity is defined as the rate of change of Position. Radius of curvature is a term characterizing the measure of how curved or bent a given Curve or Surface is For example, a racing car driver travelling at 50 m/s around a corner with radius of curvature 80 m undergoes an acceleration of 50²/80 m/s², or 31. 25 m/s². This equates to a g-force of about 31. 25/9. 8 g, or about 3. 19 g (again, for the purposes of this example, ignoring the additional g-force due to Earth's gravity).

Examples of usage

• The g is used in the aerospace industry, where it is a convenient magnitude when specifying the maximum load factor which aircraft and spacecraft must be capable of withstanding. This article is about the field of research and industry for the corporation see The Aerospace Corporation Aerospace comprises the Load factor is the Ratio of the Lift on an Aircraft to the Weight of the aircraft A spacecraft is a Vehicle or machine designed for Spaceflight. Light airplanes of the kind used in pilot training (utility category) must be capable of sustaining an upper load factor of 4. 4 g (43 m/s², 141. 5 ft/s²) with the undercarriage retracted. ^{FAR §23. 337} Airline airplanes and other airplanes in the transport category must be capable of an upper load factor of 2. Transport category is a category of airworthiness applicable to large civil airplanes and large civil helicopters 5 g. ^{FAR §25. 337} Military aircraft and pilots (especially fighter pilots) with pressure suits can experience up to 9 g. A fighter pilot is a military aviator trained to engage other aircraft and typically pilots a Fighter aircraft.
• The g is used in automotive engineering, mainly in relation to cornering forces and collision analysis.
• The g is used to express the amount of acceleration/shock force a device or component part of a device can withstand. A mechanical or physical shock is a sudden Acceleration or deceleration caused for example by impact drop kick Earthquake, or Explosion. For example, mechanical wrist-watches might withstand 7 g, aerospace rated relays might withstand 50 g, and GPS IMUs units for military howitzer shells might withstand 15,500 g. A relay is an electrical Switch that opens and closes under the control of another Electrical circuit. ^[1]
• g-forces are an important factor in roller coasters and other theme park rides. The roller coaster is a popular Amusement ride developed for Amusement parks and modern Theme parks LaMarcus Adna Thompson patented the first Rides redirects here For the album by Reef see Rides (album, and for the BBC television series see Rides (TV series. They are often displayed in ride statistics.
• g-force is often used to describe a relatively long-term acceleration: A short-term acceleration is usually called a shock and is also measured in gs. A mechanical or physical shock is a sudden Acceleration or deceleration caused for example by impact drop kick Earthquake, or Explosion.

Human tolerance to g-force

Human tolerances depend on the magnitude of the g-force, the length of time it is applied, the direction it acts, the location of application, and the posture of the body.

The human body is flexible and deformable, particularly the softer tissues. A hard slap on the face may impose hundreds of g locally but not produce any real damage; a constant 16 g for a minute, however, may be deadly. When vibration is experienced, relatively low peak g levels can be severely damaging if they are at the resonance frequency of organs and connective tissues. Vibration refers to mechanical Oscillations about an equilibrium point. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's

To some degree, g-tolerance can be trainable, and there is also considerable variation in innate ability between individuals. In addition, some illnesses, particularly cardiovascular problems, reduce g-tolerance. This is an article about the rock music band "Circulatory System"

Vertical axis g-force

Aircraft, in particular, exert g-force 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.

In aircraft, g-forces are often towards the feet, which forces blood away from the head; this causes problems with the eyes and brain in particular. As g-forces increase brownout/greyout can occur, where the vision loses hue. A brownout, or grey-out, is a transient loss of vision characterised by a perceived dimming of light accompanied by a brown hue and a loss of peripheral vision If g-force is increased further tunnel vision will appear, and then at still higher g, loss of vision, while consciousness is maintained. This article refers to the medical condition For the novel see Tunnel Vision; for the film see Tunnel Vision (film; for the mural "Tunnelvision" This is termed "blacking out". Beyond this point loss of consciousness will occur, sometimes known as "g-loc" ("loc" stands for "loss of consciousness"). G-LOC, abbreviated from G-force induced Loss Of Consciousness, is a term generally used in Aerospace physiology to describe a loss of consciousness arising from While tolerance varies, a typical person can handle about 5 g (49m/s²) before g-loc'ing, but through the combination of special g-suits and efforts to strain muscles—both of which act to force blood back into the brain—modern pilots can typically handle 9 g (88 m/s²) sustained (for a period of time) or more (see High-G training). A g -suit is worn by Aviators and Astronauts who are subject to high levels of acceleration (' ''g'' ' High-G training is done by aviators and astronauts who are subject to high levels of acceleration ('G'

Resistance to "negative" or upward gees, which drive blood to the head, is much lower. This limit is typically in the −2 to −3 g (−20 m/s² to −30 m/s²) range. The subject's vision turns red, referred to as a red out. A brownout, or grey-out, is a transient loss of vision characterised by a perceived dimming of light accompanied by a brown hue and a loss of peripheral vision This is probably because capillaries in the eyes swell or burst under the increased blood pressure.

Humans can survive up to about 20 to 35 g instantaneously (for a very short period of time). Any exposure to around 100 g or more, even if momentary, is likely to be lethal, although the record is 179 g. ^[2] It has also been said that the height of a person can be shortened if high g-force is sustained for a continuous amount of time.

Horizontal axis g-force

The human body is considerably better at surviving g-forces that are perpendicular to the spine. In general when the g-force pushes the body backwards (colloquially known as "eyeballs in"^[3]) a much higher tolerance is shown than when g-force is pushing the body forwards ("eyeballs out") since blood vessels in the retina appear more sensitive in the latter direction.

Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm. ^[4]

NASA g-tolerance data

From NASA SP-3006:

Human g-force experience

• Amusement park rides such as roller coasters typically do not expose the occupants to much more than about 3 g for more than around 3 seconds at the most. Theme park is the generic term for a collection of rides and other Entertainment attractions assembled for the purpose of entertaining a large group The roller coaster is a popular Amusement ride developed for Amusement parks and modern Theme parks LaMarcus Adna Thompson patented the first Some notable exceptions are G-Force at Drayton Manor Theme Park in England, Oblivion at Alton Towers in England, Speed at Oakwood Theme Park in Wales, Jetline at Gröna Lund in Stockholm, Titan in Texas, Dragon (Adventureland) at Adventureland (Iowa) in Altoona, Iowa which all have a maximum of 4. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s Drayton Manor Theme Park is a Theme park in the grounds of the former Drayton Manor, near Tamworth in Staffordshire, England. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Oblivion is a steel Roller coaster located at Alton Towers in England. Alton Towers is a Theme park and Resort located in the grounds of a former stately home in Staffordshire, England. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Speed is a more than vertical roller coaster at Oakwood Theme Park, Pembrokeshire UK Oakwood Theme Park (formerly Oakwood Leisure Park or Oakwood Coaster Country) is a Theme park in Pembrokeshire, Wales which attracts Jetline is a Roller coaster at Gröna Lund in Stockholm, Sweden. Tivoli Gröna Lund (lit The Green Grove) is an Amusement park in Stockholm, Sweden. Titan is a Hyper coaster located at Six Flags Over Texas in Arlington Texas. Texas ( is a state geographically located in the South Central United States and is also known as the Lone Star State. The Dragon is a Steel roller coaster located at Adventureland in Altoona Iowa, near Des Moines. Adventureland is a family-owned amusement park in Altoona Iowa (just northeast of Des Moines) Altoona is a city in Polk County, Iowa, United States and a part of the Des Moines &ndash West Des Moines Metropolitan Statistical 5 g for up to 1. 3 seconds. The Superman Escape at Warner Bros. Movie World, Gold Coast, Queensland, Australia imparts 4. For the similarly named roller coaster located in California, please see Superman The Escape. Warner Bros Movie World is a popular movie related Theme park on the Gold Coast in Australia. 2 positive g and 1 negative g (most likely the fall after the massive uphill track at the start which travels from 0–100 km/h (0–60 mph)) in two seconds. SheiKra in Tampa pulls 4 g. SheiKra (ˈʃiːkrə is a vertical drop Roller coaster in Tampa Florida. ^[5] The record for the highest g-force on a roller coaster belongs to Mindbender at Galaxyland Amusement Park, Edmonton, Alberta, Canada, at 5. The Mindbender is the world's largest indoor triple loop Roller coaster. Galaxyland is the world's largest indoor Amusement park situated in the West Edmonton Mall in Edmonton Alberta, Canada. Edmonton (ˈɛdmɨntɨn is the capital of the Canadian province of Alberta. 2 g. The highest g on a thrill ride can be experienced on Detonator at Thorpe Park, England, which reaches 5. Thorpe Park is a theme park located in Surrey, United Kingdom. 5 g at the end of the drop by firing riders downwards pneumatically. Fuji-Q Highland, an amusement park in Fujiyoshida, Yamanashi, Japan, used to operate a shuttle coaster named Moonsault Scramble that subjected riders to 6. Fuji-Q Highland (富士急ハイランド is an Amusement park in Fujiyoshida, Yamanashi, Japan. 2 g in the track's high speed pretzel element. The current record for max g to date is Tower Of Terror at Gold Reef City in Johannesburg, Gauteng South Africa, with a max of 6. 3. But most notably, Goliath at Six Flags Magic Mountain in California lets riders experience 3. Goliath is a Steel roller coaster made by Giovanola of Switzerland. Six Flags Magic Mountain is an Amusement park located in Valencia, California north of Los Angeles. 792 g, making hundreds of people pass out daily. This was measured with a personal accelerometer. The force then proceedes to 4. 233 g at the end of the helix, just before it transitions into the overbank.
• A sky-diver in a stable free-fall experiences 0. 0 g (full weight) after reaching terminal velocity, but only because they are free falling. A free falling object achieves its terminal velocity when the downward force of gravity ( Fg)equals the upward force of drag ( Fd)
• Paraglider pilots can experience 6 g or more in spiral dives.
• A SCUBA diver or swimmer experiences 1 g (full weight), but buoyancy largely cancels the weight of his body. A scuba set is an independent breathing set that provides a scuba diver with the Breathing gas necessary to breathe underwater during Scuba diving. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is However, density differences do create forces. The lungs are significantly buoyant.
• Astronauts in Earth orbit experience 0 g ("weightlessness"). An astronaut or cosmonaut (космона́вт) is a person trained Weightlessness is a phenomenon experienced by people during Free-fall. They are still strongly attracted by the Earth's gravity—acceleration due to gravity at an orbital height of 600 km (372 mi) is about 83% of that at sea level. However, as they are in free fall they do not feel any acceleration.
• Passengers on planes on a parabolic trajectory experience 0 g (as in the "Vomit Comet"). In Mathematics, the parabola (pəˈræbələ from the Greek παραβολή) is a Conic section, the intersection of a right circular Trajectory is the path a moving object follows through space The object might be a Projectile or a Satellite, for example Vomit Comet is a nickname for any Airplane that briefly provides a nearly weightless environment in which to train Astronauts conduct research and
• Aerobatic and fighter pilots may experience a brownout/greyout between 6 and 9 g characterized by temporary loss of colour vision, tunnel vision, or an inability to interpret verbal commands. A brownout, or grey-out, is a transient loss of vision characterised by a perceived dimming of light accompanied by a brown hue and a loss of peripheral vision This may proceed to total loss of consciousness, known as g-LOC. G-LOC, abbreviated from G-force induced Loss Of Consciousness, is a term generally used in Aerospace physiology to describe a loss of consciousness arising from They also experience a "red-out" at negative g. These effects are mostly caused by blood pressure differences between the heart and the brain.
• NASCAR Sprint Cup driver Jeff Gordon experienced the third-highest ranked g-force crash recorded by NASCAR at the 2006 Pennsylvania 500 race at Pocono Raceway, measuring an unprecedented 64 g. Jeffery Michael Gordon The Sunoco Presents The American Red Cross Pennsylvania 500 is the second of two NASCAR Sprint Cup Series stock car races held at the Pocono Raceway Gordon reported that at the time, it was the hardest hit he ever took in a car.
• Pilots in the Red Bull Air Race commonly exceed 10 g for seconds during turns, occasionally surpassing 12 g. The Red Bull Air Race World Series, established in 2003 and created by Red Bull, is an international series of air races in which competitors have to navigate a challenging
• In 2008, astronauts aboard a Soyuz capsule were subjected to 10 g when they returned to Earth on too steep a trajectory. An astronaut or cosmonaut (космона́вт) is a person trained EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 ^[6]
• Formula One drivers usually experience 5 g while braking, 2 g while accelerating, and 4 to 6 g while cornering. Every Formula One car has an ADR (Accident Data Recovery) device installed, which records speed and g-force. According to the FIA, Robert Kubica of BMW Sauber experienced 75 g during his 2007 Canadian Grand Prix crash. Robert Kubica ( /'rɔbɛrt ku'bitsa/ ("koo-bit-sa" born December 7, 1984 in Kraków, Poland) is the first Polish BMW Sauber F1 are a Formula One team with bases in Hinwil, Switzerland and Munich, Germany. The Canadian Grand Prix (known in French as the Grand Prix du Canada) is an auto race held in Canada since 1961. ^[7]

Everyday g-forces

• 3. 5 g during a cough. ^[8][9]
• 2. 9 g during a sneeze. ^[8][9]

Highest g-forces survived by humans

Voluntary

Colonel John Stapp in 1954 sustained 46. John Paul Stapp, MD PhD Colonel USAF (Ret ( 11 July 1910 &ndash 13 November 1999) was a pioneer in studying the effects of acceleration 2 g in a rocket sled, while conducting research on the effects of human deceleration. ^[10][11]

Involuntary

Formula One racing car driver David Purley survived an estimated 179. David Charles Purley GM ( January 26, 1945 - July 2, 1985) was a British Racing driver born in Bognor Regis, 8 g in 1977 when he decelerated from 173 km/h (108 mph) to rest over a distance of 66 cm (26 inches) after his throttle got stuck wide open and he hit a wall. ^[2]

Indy Car driver Kenny Bräck crashed on lap 188 of the 2003 race at Texas Motor Speedway. Kenneth "Kenny" Brack (born March 21, 1966 in Arvika, Värmland) is a Race car driver from Sweden. Texas Motor Speedway is a speedway located in the northernmost portion of the U Bräck and Tomas Scheckter touched wheels, sending Bräck into the air at 200+ mph, hitting a steel support beam for the catch fencing. Tomas Scheckter (born September 21, 1980) is a South African racing driver born in Monte Carlo, currently competing in the Indy Racing According to Bräck's site his car recorded 214 g. ^[12]

See also

• Cushioning
• Earth's gravity
• Load factor
• Shock (mechanics)

References

External links

• Wired article about enduring a human centrifuge at the NASA Ames Research Center
• eXtreme High Altitude Calculator - value of g at any altitude
• Video of Pilot g-force training