And that’s exactly how accelerating at 64 feet per second, per second - or twice the force of gravity - will make your body feel. Which we’ve all experienced on rollercoasters for fractions of seconds. But for pilots, sustained G Force of 5.5 G (5.5 x the force of gravity) for more than four seconds is life threatening and sometimes fatal. Maybe man wasn’t supposed to fly after all.
In layman’s terms, G Force is simply the force of gravity - the thing that prevents most humble folk from being able to dunk or the natural rate at which you’d fall (32 feet per second, per second) if you were unlucky enough to step into a sinkhole. As we found out from physicist and popular science author Dr. Mark Denny, it’s not the speed you gather that’s most dangerous but the rate at which you gather it - acceleration. Traveling at 1 G means accelerating at 22 mph per second. And the quicker you continuously accelerate, the more G-s you experience. And the more internal pain your body suffers.
THE RED BULLETIN: In layman’s terms, what is G Force?
MARK DENNY: G-force is a measure of acceleration. If you stomp on the accelerator of your Thunderbird Super Coupe, it might take you from zero to 60 in 7 seconds, which is an acceleration of 0.87 G. You feel this acceleration as the force that presses you back in the seat. By definition, 1 G is the rate at which you accelerate towards the surface of the Earth - except that you don’t, because the ground holds you up. So imagine the ground giving way beneath you and falling into a sinkhole, you would be accelerating at 1 G.
So the quicker you accelerate, the harder you’re pushed into the back of the driver’s seat?
If you weigh 200 lbs. on the surface of the Earth and you are transported to a planet that has a surface acceleration three times greater than that on Earth, 3 G, then you would weigh 600 lbs. Same goes for traveling at 3 G in a car or a jet. That’s how heavy you’d feel at that speed.
A G-force of 1 G acting on, say, a car will cause the car to increase its speed by 32 feet per second (22 mph) for every second that the force acts. So at first the car is standing still, then a second later it is moving at 22 mph, two seconds later it is moving at 44 mph, and so on.
Let’s say we hit 3 G and that’s 500mph. Once there’s no more accelerating and the vehicle is maintaining that speed, am I still experiencing G Force?
If the acceleration stops when you are at 500 mph then there is no more G force and you coast along at 500 mph. The quicker you accelerate per second, the more G force you experience.
What about roller coasters, bungee jumping or skydiving?
You fall at about 1 G (actually a little faster, but that is a complication). But when the bungee stretches, you decelerate at a rate that might be greater than 1G. So far as rollercoasters go, the G force is limited, and so is the time over which it acts, so it’s not dangerous.
What about in a car crash?
G-forces can be negative as well as positive, and can get a whole lot greater than 1 G. Say you hit a wall in your T-bird at 60 mph. You come to a sudden halt in about 0.08 seconds, corresponding to a deceleration (negative acceleration) of about 35 G - almost certainly fatal. That’s 1,120 feet per second per second (cumulative speed).
So what happens to your body under G-force?
We know a lot about this, because the USAF has studied G-s on their pilots, who experience big G-s when pulling out of a dive. The most obvious effect is that the pilot feels heavier, as we saw, earlier depending on the G-force.
Most worrying is the loss of blood to the head. Imagine a spin drier at high speed - water is thrown out of clothing, which is held in a drum. A pilot is held in his seat, but his blood drains from head to feet, and his heart has trouble pumping blood back up to his head so he can grey-out or black out entirely depending on his position and the G-force, strength and duration, If he experiences 5.5 G for 3 or 4 seconds, that will be enough to knock him or her out.
For pilots, it helps a lot if they have an anti-G suit, which compresses the legs so the blood can’t pool in the lower body. At high G-force the blood may burst many blood vessels in your lower body and actually puncture the skin, forming red blotches that look like measles - sometimes called ‘Geasles’.
If G-force increases, or persists for a few seconds, a pilot starts to suffer progressive loss of sight—first peripheral vision goes (tunnel vision) and then a loss of vision and eventually blacking out entirely, which comes back to the lack of blood to the brain.
Once the G-force ceases, the pilot regains consciousness after about 12 seconds, though he or she is confused and mentally incapable of flying a plane for several seconds after regaining consciousness.