Frames of Reference

The Physics Hypertextbook™
© 1998-2008 by Glenn Elert -- A Work in Progress
All Rights Reserved -- Fair Use Encouraged

prev | up | next

Discussion

introduction

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).

Vertical Accelerations
gz (g) event or symptom
16 R. F. Gray, centrifuge*, 1958
12 - 14 ejection seat
11.4 Greg Poe, aerobatic airplane, 2002
4.5 - 6.3 loss of consciousness for most people
3.9 - 5.5 complete loss of vision (blackout)
3.4 - 4.8 partial loss of vision (grayout)
4.5 roller coaster, maximum at bottom of first dip
1 surface of the earth (not accelerating), accelerating at 1 g in deep space
⅙ surface of the moon (not accelerating)
0 free fall, ballistic trajectory, orbit (apparent weightlessness)
-1 congestion of blood in head
-2 severe blood congestion, throbbing headache, reddening of vision (redout)
-5 limit of sustained human tolerance
 
Horizontal Accelerations
gx (g) event or symptom
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
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 crash-survivable memory units (for flight data/voice recorder), impact acceleration limit
* 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 lying on their backs) are accelerated in the direction of their horizontal axes.

Finish

the vomit comet

KC-135

[T]he 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

Summary

Problems

practice

  1. Elevator problem.
    • Answer it.
  2. Write something else.
    • Answer it.
  3. Write something different.
    • Answer it.
  4. Write something completely different.
    • Answer it.

conceptual

  1. Is the frame of reference acceleration greater than, less than, or equal to normal earth gravity on the space shuttle as it …
    1. ascends to orbit,
    2. orbits, and
    3. reenters the earth's atmosphere?

numerical

  1. NASA has two ground-based facilities for studying the effects of apparent weightlessness — the above ground 2.2 Second Drop Tower and the subterranean 5 Second Drop Tower (a.k.a. the Zero-Gravity Research Facility). Both are located in Cleveland, Ohio and are associated with NASA's Glenn Research Center. Both are long vertical rooms where experiment packages are dropped in a minimal air resistance environment, briefly simulating weightlessness. The table below gives two key characteristics for each drop tower. Determine the other remaining characteristics and complete the table.
     
    NASA Drop Towers
    characteristic 2.2 s drop tower 5 s drop tower
    overall length (m) 155.5
    free fall duration (s) 5.15
    free fall distance (m) 24.1
    impact velocity (m/s)
    deceleration duration (s) 0.2
    deceleration distance (m)
    impact deceleration (m/s2)
    impact frame of reference (g)
     

Resources

prev | up | next

Another quality webpage by

Glenn Elert		 eglobe logo home | contact

bent | chaos | eworld | facts | physics