The dude went even faster than originally thought.

Mark

Mach 1.25 is pretty impressive, but it was his heart rate that surprised me considering he was not really that active.

My heart would have burst.

It's the G force that confused me. Presumably that was when he opened the parachute? Curious that his head and body accelerated at such different rates; 2 and 3.5 respectively!

I'm guessing they were measuring the G from rotation as well as acceleration due to gravity.

If he was spinning about his centre of mass then his feet would be further away than his head and so his feet would experience a higher G force.

I can't really see any other way of achieving different G forces on different parts of the body.

That makes sense; the ratio is about right. So, if he was 2 meters tall and the CoG split him 4:7 we should be able to work out the force.

Radius r of pedal orbit = 14/11 meters x sin(angle of tilt).
Angular velocity w is 60RPM = 2xPi radians per second

Taking the angle as 90 degrees to give an upper bound; Acceleration = r w^2 = 50.24 m/s^2

Taking G = 9.8m/s^2 gives 5G

So yeah, you're correct! He must have been tilted at about 45 degrees, giving a G force of 3.5 at the feet.

(8+|

Mark

Er.. if he was experiencing absolute weightlessness, he wouldn't be falling...

Huh? He was experiencing weightlessness because he was falling, without significant resistance. Acceleration is equivalent to gravity, and in his case they mostly cancelled out.

The way they phrased it makes no sense. Objects which are falling do not lose weight as they do so. if you throw a ball up in the air it's not weightless as it falls, it's weightless at the exact top of it's arc. I draw your attention to the diagram used to illustrate the flight of NASA's 'vomit comet'. Note where the zone of zero G is...



He was never climbing fast enough to experience that. You don't cancel out gravity with velocity, you cancel it with an opposing force (i.e. acceleration in an opposite direction). The only opposing force was air resistance which mostly increased as he fell, not decreased. There was (presumably) one point in his fall where the deceleration due to air resistance was exactly 1G and his delta-v would have been exactly zero. Maybe for that split second, he could be considered to be weightless. But for 25 seconds? At the beginning? If he'd been weightless for 25 seconds at the start, he'd never have gained enough velocity to get going and we'd have had to send a balloon up to rescue him somehow. If he'd have been weightless as he jumped out of the capsule he'd have stayed more or less where he was. He patently didn't.

And in any case, I also draw your attention to the word 'absolute'. At no point in his fall was he absolutely weightless, since 'weight' is never absolute. If they can't even get that right, I don't particularly trust their numbers.

It's very likely he experienced something that felt similar to weightlessness as he would have had no objects in sight that were useful to gain a sense of perspective, so for a period it would have felt to him like he was just hanging in space even though in fact he was falling very very fast. But that's not the same thing.

What he did was utterly amazing. But let's dignify dodgy journalism on the back of it.

Who said anything about velocity? He was accelerating at close to 9.8m/s/s while he was in free-fall, and as I said the acceleration mostly cancelled out the force due to gravity from his perspective.

Mostly, not entirely, but the air resistance was minimal.

In your diagram, the plane is also in free-fall for the duration marked as Zero-g. In this case, the plane has an initial vertical velocity so it continues to rise for the first part - but it is in free fall. It then reaches zero vertical velocity, and at that point it's no different from a man jumping out of a stationary balloon.

Although of course, once again, it's not zero-g. It's nearly zero-g, because of the slight air resistance. In both cases, drag has been reduced as far as possible by a combination of aerodynamics and high altitude.

I think perhaps you're confusing weight and mass.

His mass remained constant. No one is saying otherwise.

However, from the point of view of his frame he was (nearly) weightless. Not massless; weightless. Weight is the experience of the force of gravity acting on your mass, and from his frame of reference there was very little force experienced.