The Physics
Opus in profectus

Frames of Reference

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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:

Vertical frame of reference accelerations
gz (g) device, event, phenomenon, process
−5 limit of sustained human tolerance
−2 severe blood congestion, throbbing headache, reddening of vision (redout)
−1 congestion of blood in head
0 free fall, ballistic trajectory, orbit (apparent weightlessness)
~⅙~ surface of the moon (not accelerating)
1 surface of the Earth (not accelerating), accelerating at 1 g in deep space
4.5 roller coaster, maximum at bottom of first dip
3.4–4.8 partial loss of vision (grayout)
3.9–5.5 complete loss of vision (blackout)
4.5–6.3 loss of consciousness (LOC) for most people
11.4 Greg Poe, aerobatic airplane, 2002
12–14 ejection seat
16 R.F. Gray, centrifuge*, 1958
Horizontal frame of reference 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 ascent, the space shuttle is accelerated in the direction of its vertical axis, but the passengers (who are laying back in their seats) are accelerated in the direction of their horizontal axes.
gx (g) device, event, phenomenon, process
0 stationary or moving at a constant velocity
0.4 "pedal to the metal" in a typical American car
0.8 "pedal to the metal" in a high performance sports car
1.7 "pedal to the metal" in a Formula One race car
2 Extreme Launch roller coaster at start
2.96 Fastest 0–100 km/h by an electric car, average, 2023
3.81 Fastest 0–100 km/h by an electric car, peak, 2023
3 space shuttle, maximum at takeoff; jet fighter landing on aircraft carrier
8 limit of sustained human tolerance
31.25 R.F. Gray, centrifuge*, 5 s duration, 1959
40 USAF chimpanzee, centrifuge*, 60 s duration, 1956
35–40 J.P. Stapp, rocket powered impact sled, 1 s duration, 1954
60 chest acceleration limit during car crash at 48 km/h with airbag
70–100 crash that killed Diana, Princess of Wales, 1997
83 E.L. Beeding, rocket powered impact sled, 0.04 s duration, 1958
247 USAF chimpanzee, rocket powered impact sled, 0.001 s duration, 1957
3400 flight data/voice recorder, impact acceleration limit