frames Discussion


Newtonian relativity: absolute linear motion at a constant velocity cannot be detected, nor can absolute rest. All motion is relative to a frame of reference. It is not possible to distinguish motion with a constant velocity from rest. All constant velocity frames of reference are equivalent (including frames of reference that appear to be at rest — after all, a prolonged state of rest is motion with a constant speed of zero).


the vomit comet


The maneuver can be modified to provide any level of g-force less than one g. Some typical g-levels used on different tests and the corresponding time for each maneuver are as follows:

  • Negative-g: (-0.1 g): Approximately 15 seconds
  • Zero-g: (0 g) Approximately 25 seconds
  • Lunar-g: (⅙ g): Approximately 30 seconds
  • Martian-g: (⅓ g): Approximately 40 seconds
Vertical accelerations
gz (g)event or symptom
-5limit of sustained human tolerance
-2severe blood congestion, throbbing headache, reddening of vision (redout)
-1congestion of blood in head
0free fall, ballistic trajectory, orbit (apparent weightlessness)
surface of the moon (not accelerating)
1surface of the Earth (not accelerating), accelerating at 1 g in deep space
4.5roller coaster, maximum at bottom of first dip
3.4–4.8partial loss of vision (grayout)
3.9–5.5complete loss of vision (blackout)
4.5–6.3loss of consciousness for most people
11.4Greg Poe, aerobatic airplane, 2002
12–14ejection seat
16R.F. Gray, centrifuge*, 1958
Horizontal accelerations* The passenger capsule of a human centrifuge pivots so that a test subject in a seat would experience a vertical acceleration while a test subject lying down would experience a horizontal acceleration. During lift off, the space shuttle (which is pointing more or less upward) is accelerated in the direction of its vertical axis, but the passengers (who are hanging upside down in their seats) are accelerated in the direction of their horizontal axes.

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