Gravitational Forces Flashcards
“G”
Measure of magnitude of accel force with respect to gravity
9.8m/s/s or 32.2 ft/s/s (until terminal velocity is reached)
Acceleration
Rate of change in velocity with respect to time
Gravity is most common accelerative force
Deceleration
Reduction of velocity of a moving object with respect to time (negative accel)
John Paul Stapp: 0-632mph in 5.4 sec; 632-0mph in 1.4 sec!
Inertial Force
Resistance to change in motion OR rest
Newton’s First Law: Body at motion stays in motion until force acts upon it
Newton’s Third Law: For every action there is an equal/opposite reaction
Tri-Axial Reference System
+Gx -Gx -> forward and backward reference (+Gx body forced into seat in forward accel)
+Gy -Gy -> left and right reference (+Gy body forced left during right turn)
+Gz -Gz -> down and up reference (+Gz body pushed down as upward accel increases)
Factors affecting accelerative forces
Body area/site - greater size of area, less severe effects
Intensity - greater intensity, more severe effects (closely related to duration)
Rate of onset - faster the rate of accel, the more severe the effects
Duration - longer the force is applied, more severe the effects
Impact direction - force in Gy axis not as well tolerated as other axis’ due to aircraft structural and human physiological limitations
Low magnitude accel
G’s ranging from 1-10 G’s and lasting for several seconds
Longer periods of lower G’s can still cause circulatory disfunction, even unconsciousness
Systolic blood pressures at 1G
Healthy adult 120/80mm Hg
Factors DECREASING G Tolerance
Blood volume/pressure decrease due to:
- Dehydration
- Fatigue
- Hemorrhage
- Acute alcohol abuse
- Varicose veins - spiderweb looking veins, damaged/low elastic blood vessels that can cause blood pooling
Factors INCREASING G tolerance
Asymptomatic hypertension
Fear/excitement
Tensing of muscles
Short, stocky build
L-1 maneuver
Anti-G suit
Sustained Positive Accel (+Gz)
Acceleration headward (upward)
1-2.5 Gz) blood pooling
- 5-4.0 +Gz) grey out (vision going grey, fuzzy)
- 0-4.5 +Gz) black out (vision goes black)
- 5-5.0 +Gz) unconsciousness
Sustained negative acceleration (-Gz)
Acceleration foot-ward
0-1 -Gz) blood pooling
1-2.5 -Gz) vision affected
2.5-3 -Gz) red out (from the blood)
3-up -Gz) incapacitation
+/- Gx forces
Mild transverse accelerations/decelerations during landing and taking off
Tolerance: greater than +/- 7 G’s breathing may be difficult
+/- 20 G’s for several seconds without severe effects
+/- Gy forces
Human body has minimal tolerance to left/right accel
Most aircraft do not tolerate accel forces in the lateral (Gy) direction
High magnitude acceleration
G-forces exceeding 10 G’s and lasting less than a second
Some sources: aircraft crash, ejection seats, parachutes
