gforce
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Typical examples of g-force
Example g-force
The gyro rotors in Gravity Probe B and the free-floating
proof masses in the TRIAD I navigation satellite[15] exactly 0 g
A ride in the Vomit Comet approximately 0 g
Standing on the Moon at its equator 0.1654 g
Standing on the Earth at sea level–standard 1 g
Saturn V moon rocket just after launch 1.14 g
Space Shuttle, maximum during launch and reentry 3 g
High-g roller coasters[16] 3.5–6.3 g
Formula One car, maximum under heavy braking 5 g
Standard, full aerobatics certified Glider +7/-5 g
Apollo 16 on reentry[17] 7.19 g
Typical max. turn in an aerobatic plane or fighter jet 9-12 g
Maximum for human on a rocket sled 46.2 g
Death or serious injury likely >50 g
Sprint missile 100 g
Brief human exposure survived in crash[14] >100 g
Rampage Jackson body slam.[2] >400 g
Shock capability of mechanical
wrist watches[18] >5000 g
Rating of electronics built into military artillery shells[19] 15,500 g
9 × 19 Parabellum handgun bullet
(average along the length of the barrel)[20] 31,000 g
9 × 19 Parabellum handgun bullet, peak[21] 190,000 g
[edit] Measuring g-force using an accelerometer
Six Flags' “Superman: The Escape” amusement ride provides 6.5 seconds of ballistic weightlessness.
Accelerometers are often calibrated 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 g, and it will continue to be 0 g if mounted in an automobile traveling at a constant velocity on a level road. But if the car driver brakes sharply, the accelerometer will read about −0.9 g, corresponding to a deceleration.
However, if the accelerometer is rotated by 90°, so that its axis points upwards, it will read +1 g upwards even though still 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, and the reading is the acceleration the instrument would have if it were exclusively subject to that force (accelerometers measure only the mechanical components of accelerations, and thus directly read "g-force" acceleration only).
A three-axis accelerometer will output zero‑g on all three axes if it is dropped or otherwise put into a 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 notable amusement park rides can provide several seconds at near-zero g. Riding NASA’s “Vomit Comet” provides near-zero g for about 25 seconds at a time.
A single-axis accelerometer mounted in an airplane with its measurement axis oriented vertically reads +1 g when the plane is parked. This is the "g-force" exerted by the ground. When flying at a stable altitude (or at a constant rate of climb or descent), the accelerometer will continue to indicate 1 g, as the g-force is provide by the aerodynamic lift. Under such conditions, the downward force acting upon the pilot’s body is the normal value of about 9.8 newtons per kilogram (N/kg) (one pound-force per pound). If the pilot pulls back on the stick until the accelerometer indicates 2 g, his weight (the force acting downwards on him) will double to 19.6 N/kg. A spring-based weighing scale, for the duration of a 2 g pitch-up maneuver, would reveal that his weight has truly doubled; a pilot who normally weighs 160 pounds would momentarily weigh 320 pounds. Again the forces measured are the mechanical forces provided by the seat and body of the airplane, pushing the accelerometer and the pilot upward and away from the path of free fall.
[edit] See also
* Earth's gravity
* Metre per second squared
* Impact (mechanics)
* Shock (mechanics)
* Jerk (physics)
* Load factor (aerodynamics)
* Thrust-to-weight ratio
[edit] References
1. ^ Cite Error: Invalid <ref> tag; no text was provided for refs named eshbach.
2. ^ [1]
3. ^ Note that the unit does not vary with location- the g-force when standing on the moon is about 0.18g
4. ^ Symbol g: ESA: GOCE, Basic Measurement Units, NASA: Multiple G, Astronautix: Stapp, Honeywell: Accelerometers, Sensr LLC: GP1 Programmable Accelerometer, Farnell: accelometers, Delphi: Accident Data Recorder 3 (ADR3) MS0148, NASA: Constants and Equations for Calculations, Jet Propulsion Laboratory: A Discussion of Various Measures of Altitude, Vehicle Safety Research Centre Loughborough: Use of smart technologies to collect and retain crash information, National Highway Traffic Safety Administration: Recording Automotive Crash Event Data
Symbol G: Lyndon B. Johnson Space Center: ENVIRONMENTAL FACTORS: BIOMEDICAL RESULTS OF APOLLO, Section II, Chapter 5, Honywell: Model JTF, General Purpose Accelerometer
Symbol g: MEMSIC: ACCELEROMETER PRIMER
5. ^ Cite Error: Invalid <ref> tag; no text was provided for refs named ESA.
6. ^ BIPM: Declaration on the unit of mass and on the definition of weight; conventional value of gn
7. ^ The Ejection Site: The Story of John Paul Stapp
8. ^ Balldin, Ulf I (2002). "33". Acceleration effects on fighter pilots. In: Medical conditions of Harsh Environments. 2. Washington, DC. . Retrieved 2009-04-06.
9. ^ Beyond the Black Box: the Forensics of Airplane Crashes; George Bibel, John Hopkins University Press, 2008 (ISBN 0-8018-8631-7), p350
10. ^ Burton RR (January 1988). "G-induced loss of consciousness: definition, history, current status". Aviation, Space, and Environmental Medicine 59 (1): 2–5. PMID 3281645.
11. ^ NASA Physiological Acceleration Systems
12. ^ NASA Technical note D-337, Centrifuge Study of Pilot Tolerance to Acceleration and the Effects of Acceleration on Pilot Performance, by Brent Y. Creer, Captain Harald A. Smedal, USN (MC), and Rodney C. Vtlfngrove
13. ^ http://www.ejectionsite.com/stapp.htm
14. ^ a b “Several Indy car drivers have withstood impacts in excess of 100 G without serious injuries.” Dennis F. Shanahan, M.D., M.P.H.: ”Human Tolerance and Crash Survivability, citing Society of Automotive Engineers. Indy racecar crash analysis. Automotive Engineering International, June 1999, 87-90. And National Highway Traffic Safety Administration: Recording Automotive Crash Event Data
15. ^ Stanford University: Gravity Probe B, Payload & Spacecraft, and NASA: 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, or NAVSAT system.
16. ^ Beyond the Black Box: the Forensics of Airplane Crashes; George Bibel, John Hopkins University Press, 2008 (ISBN 0-8018-8631-7), p340
17. ^ NASA: Table 2: Apollo Manned Space Flight Reentry G Levels
18. ^ Omega FAQ, Ball Watch Technology
19. ^ "L-3 Communication's IEC Awarded Contract with Raytheon for Common Air Launched Navigation System". .
20. ^ Assuming a 124 grain (8.04 gram) bullet, a muzzle velocity of 1,150 feet per second (350 m/s), and a 4‑inch (102 mm) barrel.
21. ^ Assuming a 124 grain (8.04 gram) bullet, a peak pressure of 35,000 psi (240 MPa) and 100 pounds (440 N) of friction.
[edit] External links
* Wired article about enduring a human centrifuge at the NASA Ames Research Center
* Video of Pilot g-force training
* Official Red Bull Air Race G-Force explanation
Retrieved from "http://en.wikipedia.org/wiki/G-force"
Categories: Units of acceleration | Gravimetry
Hidden categories: Pages with broken reference names | All articles with unsourced statements | Articles with unsourced statements from August 2009
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* This page was last modified on 19 August 2009 at 14:54.
Example g-force
The gyro rotors in Gravity Probe B and the free-floating
proof masses in the TRIAD I navigation satellite[15] exactly 0 g
A ride in the Vomit Comet approximately 0 g
Standing on the Moon at its equator 0.1654 g
Standing on the Earth at sea level–standard 1 g
Saturn V moon rocket just after launch 1.14 g
Space Shuttle, maximum during launch and reentry 3 g
High-g roller coasters[16] 3.5–6.3 g
Formula One car, maximum under heavy braking 5 g
Standard, full aerobatics certified Glider +7/-5 g
Apollo 16 on reentry[17] 7.19 g
Typical max. turn in an aerobatic plane or fighter jet 9-12 g
Maximum for human on a rocket sled 46.2 g
Death or serious injury likely >50 g
Sprint missile 100 g
Brief human exposure survived in crash[14] >100 g
Rampage Jackson body slam.[2] >400 g
Shock capability of mechanical
wrist watches[18] >5000 g
Rating of electronics built into military artillery shells[19] 15,500 g
9 × 19 Parabellum handgun bullet
(average along the length of the barrel)[20] 31,000 g
9 × 19 Parabellum handgun bullet, peak[21] 190,000 g
[edit] Measuring g-force using an accelerometer
Six Flags' “Superman: The Escape” amusement ride provides 6.5 seconds of ballistic weightlessness.
Accelerometers are often calibrated 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 g, and it will continue to be 0 g if mounted in an automobile traveling at a constant velocity on a level road. But if the car driver brakes sharply, the accelerometer will read about −0.9 g, corresponding to a deceleration.
However, if the accelerometer is rotated by 90°, so that its axis points upwards, it will read +1 g upwards even though still 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, and the reading is the acceleration the instrument would have if it were exclusively subject to that force (accelerometers measure only the mechanical components of accelerations, and thus directly read "g-force" acceleration only).
A three-axis accelerometer will output zero‑g on all three axes if it is dropped or otherwise put into a 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 notable amusement park rides can provide several seconds at near-zero g. Riding NASA’s “Vomit Comet” provides near-zero g for about 25 seconds at a time.
A single-axis accelerometer mounted in an airplane with its measurement axis oriented vertically reads +1 g when the plane is parked. This is the "g-force" exerted by the ground. When flying at a stable altitude (or at a constant rate of climb or descent), the accelerometer will continue to indicate 1 g, as the g-force is provide by the aerodynamic lift. Under such conditions, the downward force acting upon the pilot’s body is the normal value of about 9.8 newtons per kilogram (N/kg) (one pound-force per pound). If the pilot pulls back on the stick until the accelerometer indicates 2 g, his weight (the force acting downwards on him) will double to 19.6 N/kg. A spring-based weighing scale, for the duration of a 2 g pitch-up maneuver, would reveal that his weight has truly doubled; a pilot who normally weighs 160 pounds would momentarily weigh 320 pounds. Again the forces measured are the mechanical forces provided by the seat and body of the airplane, pushing the accelerometer and the pilot upward and away from the path of free fall.
[edit] See also
* Earth's gravity
* Metre per second squared
* Impact (mechanics)
* Shock (mechanics)
* Jerk (physics)
* Load factor (aerodynamics)
* Thrust-to-weight ratio
[edit] References
1. ^ Cite Error: Invalid <ref> tag; no text was provided for refs named eshbach.
2. ^ [1]
3. ^ Note that the unit does not vary with location- the g-force when standing on the moon is about 0.18g
4. ^ Symbol g: ESA: GOCE, Basic Measurement Units, NASA: Multiple G, Astronautix: Stapp, Honeywell: Accelerometers, Sensr LLC: GP1 Programmable Accelerometer, Farnell: accelometers, Delphi: Accident Data Recorder 3 (ADR3) MS0148, NASA: Constants and Equations for Calculations, Jet Propulsion Laboratory: A Discussion of Various Measures of Altitude, Vehicle Safety Research Centre Loughborough: Use of smart technologies to collect and retain crash information, National Highway Traffic Safety Administration: Recording Automotive Crash Event Data
Symbol G: Lyndon B. Johnson Space Center: ENVIRONMENTAL FACTORS: BIOMEDICAL RESULTS OF APOLLO, Section II, Chapter 5, Honywell: Model JTF, General Purpose Accelerometer
Symbol g: MEMSIC: ACCELEROMETER PRIMER
5. ^ Cite Error: Invalid <ref> tag; no text was provided for refs named ESA.
6. ^ BIPM: Declaration on the unit of mass and on the definition of weight; conventional value of gn
7. ^ The Ejection Site: The Story of John Paul Stapp
8. ^ Balldin, Ulf I (2002). "33". Acceleration effects on fighter pilots. In: Medical conditions of Harsh Environments. 2. Washington, DC. . Retrieved 2009-04-06.
9. ^ Beyond the Black Box: the Forensics of Airplane Crashes; George Bibel, John Hopkins University Press, 2008 (ISBN 0-8018-8631-7), p350
10. ^ Burton RR (January 1988). "G-induced loss of consciousness: definition, history, current status". Aviation, Space, and Environmental Medicine 59 (1): 2–5. PMID 3281645.
11. ^ NASA Physiological Acceleration Systems
12. ^ NASA Technical note D-337, Centrifuge Study of Pilot Tolerance to Acceleration and the Effects of Acceleration on Pilot Performance, by Brent Y. Creer, Captain Harald A. Smedal, USN (MC), and Rodney C. Vtlfngrove
13. ^ http://www.ejectionsite.com/stapp.htm
14. ^ a b “Several Indy car drivers have withstood impacts in excess of 100 G without serious injuries.” Dennis F. Shanahan, M.D., M.P.H.: ”Human Tolerance and Crash Survivability, citing Society of Automotive Engineers. Indy racecar crash analysis. Automotive Engineering International, June 1999, 87-90. And National Highway Traffic Safety Administration: Recording Automotive Crash Event Data
15. ^ Stanford University: Gravity Probe B, Payload & Spacecraft, and NASA: 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, or NAVSAT system.
16. ^ Beyond the Black Box: the Forensics of Airplane Crashes; George Bibel, John Hopkins University Press, 2008 (ISBN 0-8018-8631-7), p340
17. ^ NASA: Table 2: Apollo Manned Space Flight Reentry G Levels
18. ^ Omega FAQ, Ball Watch Technology
19. ^ "L-3 Communication's IEC Awarded Contract with Raytheon for Common Air Launched Navigation System". .
20. ^ Assuming a 124 grain (8.04 gram) bullet, a muzzle velocity of 1,150 feet per second (350 m/s), and a 4‑inch (102 mm) barrel.
21. ^ Assuming a 124 grain (8.04 gram) bullet, a peak pressure of 35,000 psi (240 MPa) and 100 pounds (440 N) of friction.
[edit] External links
* Wired article about enduring a human centrifuge at the NASA Ames Research Center
* Video of Pilot g-force training
* Official Red Bull Air Race G-Force explanation
Retrieved from "http://en.wikipedia.org/wiki/G-force"
Categories: Units of acceleration | Gravimetry
Hidden categories: Pages with broken reference names | All articles with unsourced statements | Articles with unsourced statements from August 2009
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* This page was last modified on 19 August 2009 at 14:54.
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