The nominal acceleration due to gravity at sea level on the Earth's surface, also known as standard gravity, is defined as exactly 9.80665 m/s² (approx. 32.174 ft/s²). It is equivalent to 1 g (pronounced gee) which is a non-SI unit of acceleration; g-force or g-load is a force-equivalent, equal to 9.80665 N/kg. For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... Cover of brochure The International System of Units. ... Acceleration is the time rate of change of velocity, and at any point on a velocity-time graph, it is given by the slope of the tangent to that point In physics or physical science, acceleration (symbol: a) is defined as the rate of change (or derivative with respect to...

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 abbreviation for gram, which is not italicized. The conventional value was established by the 3rd CGPM (1901, CR 70). According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... BIC pen cap, about 1 gram. ... The Conférence générale des poids et mesures (General Conference on Weights and Measures or CGPM) is one of the three organizations established to maintain the SI system under the terms of the Metre Convention (1875). ...

Explanation

The total acceleration of a body is found by vector addition of the opposite of the actual acceleration (in the sense of rate of change of velocity) and a vector of 1 g downward for the ordinary gravity (or in space, the gravity there). For example, being accelerated upward with an acceleration of 1 g doubles the experienced weight. Conversely, weightlessness means an acceleration of 1 g downward in an inertial reference frame. Therefore, the term μg-force is a comparative measure of acceleration applied to a body with respect to sea-level gravity on earth. It is a normalized force vector since dividing the resultant force vector applied to a body by the body's weight (magnitude at sea level) cancels the mass, resulting in a "fractional-g" -magnitude vector, e.g. a person sitting on a chair at sea level is experiencing "1g," due to his weight. In physics and in vector calculus, a spatial vector is a concept characterized by a magnitude, which is a scalar, and a direction (which can be defined in a 3-dimensional space by the Euler angles). ... The velocity of an object is simply its speed in a particular direction. ... An objects weight, henceforth called actual weight, is the downward force exerted upon it by the earths gravity. ... Astronauts on the International Space Station display an example of weightlessness. ... Acceleration is the time rate of change of velocity, and at any point on a velocity-time graph, it is given by the slope of the tangent to that point In physics or physical science, acceleration (symbol: a) is defined as the rate of change (or derivative with respect to... Gravity is a force of attraction that acts between bodies that have mass. ... Broadly, normalization (also spelled normalisation) is any process that makes something more normal, which typically means conforming to some regularity or rule, or returning from some state of abnormality. ... In physics, force is an influence that may cause a body to accelerate. ...

The value of g defined above is an arbitrary midrange value on the Earth, approximately equal to the sea level acceleration of free fall at a geodetic latitude of about 45.5°; it is larger in magnitude than the average sea level acceleration on Earth, which is about 9.797 645 m·s⁻². The standard acceleration of free fall is properly written as g_n (sometimes g₀) to distinguish it from the local value of g that varies with position. Latitude, usually denoted symbolically by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. ...

The units of acceleration due to gravity, meters per second squared, are interchangeable with newtons per kilogram. The quantity, 9.806 65, stays the same. These alternate units may be more helpful when considering problems involving pressure due to gravity, or weight. This article is about the SI unit of force. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ... In the physical sciences, weight is a measurement of the gravitational force acting on an object. ...

Variations of Earth's gravity

Gravity varies by altitude, latitude and local variation.

On the earth's surface, the gravity will depend on the location at which it is measured, smaller at lower latitudes, for two reasons. Latitude, usually denoted symbolically by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. ...

The first is that the rotation of the Earth imposes an additional acceleration on the body that opposes gravitational acceleration. The net downward force on the body is therefore offset by a centrifugal force that acts upwards, reducing its weight. This effect on its own would result in a range of values of g from 9.789 m·s⁻² at the equator to 9.832 m·s⁻² at the poles[1]. Centrifugal force (from Latin centrum center and fugere to flee) is a term which may refer to two different forces which are related to rotation. ...

The second reason is the Earth's equatorial bulge (itself also caused by centrifugal force), which causes objects at the equator to be farther from the planet's centre than objects at the poles. Because the force due to gravitational attraction between two bodies (the Earth and the object being weighed) varies inversely with the square of the distance between them, objects at the equator experience a weaker gravitational pull than objects at the poles. An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid. ...

The combined result of these two effects is that g is 0.052 m·s⁻² more, hence the force due to gravity of an object is 0.5 % more, at the poles than at the equator.

If the terrain is at sea level, we can estimate g:

where

g_φ = acceleration in m·s⁻² at latitude φ

This is the International Gravity Formula 1967, the 1967 Geodetic Reference System Formula, Helmert's equation or Clairault's formula.

The first correction to this formula is the free air correction (FAC), which accounts for heights above sea level. Gravity decreases with height, at a rate which near the surface of the Earth is such that linear extrapolation would give zero gravity at a height of one half the radius of the Earth, i.e. the rate is 9.8 m·s⁻² per 3200 km. Thus:

where

h = height in meters above sea level

For flat terrain above sea level a second term is added, for the gravity due to the extra mass; for this purpose the extra mass can be approximated by an infinite horizontal slab, and we get 2πG times the mass per unit area, i.e. 4.2×10^-10 m³·s⁻²·kg⁻¹ (0.042 μGal·kg⁻¹·m²)) (the Bouguer correction). For a mean rock density of 2.67 g·cm⁻³ this gives 1.1×10^-6 s⁻² (0.11 mGal·m⁻¹). Combined with the free-air correction this means a reduction of gravity at the surface of ca. 2 µm·s⁻² (0.20 mGal) for every meter of elevation of the terrain. (The two effects would cancel at a surface rock density of 4/3 times the average density of the whole Earth.)

For the gravity below the surface we have to apply the free-air correction as well as a double Bouguer correction. With the infinite slab model this is because moving the point of observation below the slab changes the gravity due to it to its opposite. Alternatively, we can consider a spherically symmetrical Earth and subtract from the mass of the Earth that of the shell outside the point of observation, because that does not cause gravity inside. This gives the same result. In vector calculus, the divergence theorem, also known as Gauss theorem, Ostrogradskys theorem, or Ostrogradsky–Gauss theorem is a result that links the divergence of a vector field to the value of surface integrals of the flow defined by the field. ...

Local variations in both the terrain and the subsurface cause further variations; the gravitational geophysical methods are based on these: the small variations are measured, the effect of the topography and other known factors is subtracted, and from the resulting variations conclusions are drawn. See also physical geodesy and gravity anomaly. ‹ The template below has been proposed for deletion. ... Definition Physical geodesy is the study of the physical properties of the gravity field of the Earth, the geopotential, with a view to their application in geodesy. ... Gravity anomalies are widely used in geodesy and geophysics. ...

Calculated value of g

Given the law of universal gravitation, g is merely a collection of factors in that equation: It has been suggested that this article or section be merged into Gravity. ...

where g is the bracketed factor and thus:

To find the acceleration due to gravity at sea level you can plug in values of G and the mass (in kilograms) and radius (in meters) of the Earth to obtain the calculated value of g: Unsolved problems in physics: What causes anything to have mass? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... In classical geometry, a radius of a circle or sphere is any line segment from its center to its boundary. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ...

This agrees approximately with the measured value of g. The difference may be attributed to several factors:

• The Earth is not homogeneous
• The Earth is not a perfect sphere
• The choice of a value for the radius of the Earth (an average value is used above)
• This calculated value of g does not include the centrifugal force effects that are found in practice due to the rotation of the Earth

There are significant uncertainties in the values of r and of m₁ as used in this calculation. However, the value of G can be measured precisely and in fact, Henry Cavendish performed the reverse calculation to estimate the mass of the Earth. Look up Homogeneous in Wiktionary, the free dictionary. ... Centrifugal force (from Latin centrum center and fugere to flee) is a term which may refer to two different forces which are related to rotation. ... Henry Cavendish (October 10, 1731 - February 24, 1810) was a British scientist. ...

Usage of the unit

The g is used primarily in aerospace fields, where it is a convenient magnitude when discussing the loads on aircraft and spacecraft (and their pilots or passengers). For instance, most civilian aircraft are capable of being stressed to 4.33 g (42.5 m·s⁻², 139 ft/s²), which is considered a safe value. The g is also used in automotive engineering, mainly in relation to cornering forces and collision analysis. Look up aerospace in Wiktionary, the free dictionary. ... An Airbus A380, currently the worlds largest airliner An aircraft is any vehicle or craft capable of atmospheric flight. ... A spacecraft is a vehicle, vessel, craft or device designed to operate beyond the surface of the Earth in outer space. ... Karl Benzs Velo model (1894) - entered into the first automobile race An automobile (or motor car) is a wheeled passenger vehicle that carries its own motor. ...

One often hears the term being applied to the limits that the human body can withstand without losing consciousness, sometimes referred to as "blacking out", or g-loc (loc stands for loss of consciousness). A typical person can handle about 5 g (50 m·s⁻²) before this occurs, 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 (90 m·s⁻²) sustained (for a period of time) or more. Resistance to "negative" or upward gees which drive blood to the head, is much less. This limit is typically in the -2 to -3 g (-20 m·s⁻² to -30 m·s⁻²) range. The vision goes red and is also referred to as a "red-out". This is probably due to capillaries in the eyes bursting under the increased blood pressure. Humans can survive about 20 to 40 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. The term Faint redirects here. ... g-induced Loss Of Consciousness is a condition where a person loses consciousness because g-forces move the blood away from the brain (black out) or move excess blood towards the brain (red out). ... A G-suit is worn by aviators and astronauts subject to high levels of acceleration in order to prevent loss of consciousness, commonly called blackout or G-LOC (G-induced Loss Of Consciousness). ...

Human g-force experience

• Amusement park rides such as roller coasters typically do not expose the occupants to much more than about 3 g (some notable exceptions: the SheiKra Rollercoaster at Tampa which pulls 4 g, the Oblivion in England which does 4.5 g, the Speed Roller Coaster at Oakwood Theme Park in Wales and the Titan Rollercoaster in Texas, all three with a maximum of 4.5 g). However, the record for the most g forces on a roller coaster belongs to Mindbender at Galaxyland Amusement Park, Edmonton, Alberta, Canada, at 5.2 g. The highest negative g can be experienced on the Detonator at Thorpe Park, which reaches 5.5g at the end of the drop by firing riders downwards pneumatically. [2][3][4][5]
• A sky-diver in a stable free-fall experiences his full weight of 1 g after reaching terminal velocity.
• A scuba diver or swimmer experiences his full weight of 1 g, but buoyancy largely cancels the weight of his body. However, density differences do create forces. The lungs are significantly buoyant.
• Astronauts in Earth orbit experience 0 g, or 'weightlessness'. Although they are still strongly attracted by the Earth's gravity, they are in 'constant free fall' and therefore feel no weight.
• Passengers on planes on a parabolic trajectory experience 0 g (as in the Vomit Comet)
• Aerobatic and fighter pilots may sometimes experience a greyout between 6 and 8 g. This is not a total loss of consciousness but is characterised by temporary loss of colour vision, tunnel vision, or an inability to interpret verbal commands. They also experience a 'redout' at negative g. These effects are mostly caused by blood pressure differences between the heart and the brain.

Germany Pavilion, part of the Epcot Center theme park in Orlando, Florida Amusement park (also called theme park) is the generic term for a collection of rides and other entertainment attractions assembled for the purpose of entertaining a fairly large group of people. ... SheiKra (pronounced shee-krah) is a vertical drop roller coaster in Tampa, Florida. ... It has been suggested that Oblivion RollerCoaster be merged into this article or section. ... Motto: (French for God and my right) Anthem: God Save the King/Queen Capital London Largest city London Official language(s) English (de facto) Unification    - by Athelstan AD 927  Area    - Total 130,395 km² (1st in UK)   50,346 sq mi  Population    - 2005 est. ... Texas is the gayest motherfucking state out there they can suck my big black balls. ... Edmonton is the capital of the Canadian province of Alberta, situated in the north central region of the province, an area with some of the most fertile farm land on the prairies. ... Thorpe Parks rides and attractions from across the lake. ... The terminal velocity of an object falling towards the earth, in non-vacuum, is the speed at which the gravitational force pushing it downwards is equal and opposite to the atmospheric drag (also called air resistance) pulling it upwards. ... // SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus. ... // In physics, buoyancy is the upward force on an object arising from the displacement of the fluid (i. ... U.S. Space Shuttle astronaut Bruce McCandless II using a manned maneuvering unit (MMU) outside the Challenger in 1984. ... Earth orbit is an orbit around the planet Earth. ... Astronauts on the International Space Station display an example of weightlessness. ... A parabola A parabola (from the Greek: παραβολή) is a conic section generated by the intersection of a cone, and a plane tangent to the cone or parallel to some plane tangent to the cone. ... A trajectory is an imagined trace of positions followed by an object moving through space. ... Weightlessness inside the Vomit Comet The Vomit Comet was the nickname given to the aircraft used by NASAs Reduced Gravity Research Program. ...

Everyday g-forces

• 3.5 g during a cough. [6]
• 2.9 g during a sneeze. [7]

Strongest g-forces survived by humans

Voluntarily: Colonel John Stapp in 1954 sustained 46.2 g in a rocket sled, while conducting research on the effects of human deceleration. See Martin Voshell (2004), 'High Acceleration and the Human Body'. John Stapp rides the rocket sled at Edwards Air Force Base. ...

Involuntarily: Formula One racing car driver David Purley survived an estimated 178 g in 1977 when he decelerated from 173 km·h⁻¹ (108 mph) to 0 in a distance of 66 cm (26 inches) after his throttle got stuck wide open and he hit a wall.^[1] http://www.hypertextbook.com/physics/mechanics/acceleration/ Formula One - Wikipedia, the free encyclopedia /**/ @import /skins-1. ... David Purley (born January 26, 1945 - died July 2, 1985) was a Formula One driver born in Bognor Regis, England. ...

See also

• Earth's gravity

The acceleration due to gravity at the Earths surface, denoted g, is approximately 9. ...

References

July 31 is the 212th day (213th in leap years) of the year in the Gregorian Calendar, with 153 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ...

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