| Last night, a friend mentioned that a roller coaster in Ohio goes from zero to 120mph in 3.9 seconds. This turns out to be 13.755 m/s^2, or 1.402 G.
This prompted me to look up more about g-force and I found some interesting tidbits never learned in school, even as a mechanical engineer! I <3 wiki.
Human tolerance to g-force
Human tolerances depend on the magnitude of 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-s locally but not produce any real damage: a constant 15 g-s 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 resonant frequency of organs and connective tissues.
To some degree, g-tolerance can be trainable; and there is
also considerable variation in innate ability between individuals.
Further some illnesses reduce g-tolerance, particularly cardiovascular problems.
Vertical axis g-force
Aircraft in particular exert g-force on the axis aligned with
the spine. This causes significant variation in blood pressure along
the length of the subjects body, which limits the maximum g-forces that
can be tolerated.
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 (50m/s²) 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/s²) 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/s² to -30 m/s²) range. The vision goes red and is also referred to as a red out.
This is probably due to capillaries in the eyes swelling or 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, although the record is 179 g.[2]
Horizontal axis g-force
The human body is considerably more able to survive g-forces
that are perpendicular to the spine. In general when the acceleration
pushes the body backwards (colloquially known as 'eyeballs in'[3])
a much higher tolerance is shown than when acceleration is pushing the
body forwards ('eyeballs out') since blood vessels in the retina appear
more sensitive to that 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]
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 are Oblivion in England, Speed at Oakwood Theme Park in Wales, Jetline at Gröna Lund in Stockholm and Titan in Texas, which all have a maximum of 4.5 g, and SheiKra in Tampa which pulls 4 g.[5] 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 g on a thrill ride can be experienced on Detonator at Thorpe Park, which reaches 5.5 g at the end of the drop by firing riders downwards pneumatically.
- A sky-diver in a stable free-fall experiences 1 g (full weight) after reaching terminal velocity.
- A scuba diver or swimmer experiences 1 g (full weight), 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'.
They are still strongly attracted by the Earth's gravity. The value of
gravity acceleration at the level of a 600 km (372 mi) high orbit is
about 83% of the sea level gravity acceleration. However as they are in
free fall they don't feel any acceleration.
- 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 9 g.
This is not a total loss of consciousness but is characterized 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.
- Pilots in the Red Bull Air Race commonly exceed 10 g for seconds during turns, occasionally surpassing 12 g. [citation needed]
- Formula One drivers usually experience 5 g while braking, 2 g while accelerating, and 4 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 Montreal GP crash. [6]
Everyday g-forces
Strongest g-forces survived by humans
Voluntarily: Colonel John Stapp in 1954 sustained 46.2 g [1] in a rocket sled, while conducting research on the effects of human deceleration. See Martin Voshell (2004), 'High Acceleration and the Human Body'.
Involuntarily: Formula One racing car driver David Purley survived an estimated 179.8 g
in 1977 when he decelerated from 173 km/h (108 mph) to 0 in a distance
of 66 cm (26 inches) after his throttle got stuck wide open and he hit
a wall.[2] Cool huh :D
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