You know, this space tourism thing will just be a fad:

“It’s not really like being weightless in water,” she said. “Water has its own weight. You’re still experiencing something like a pressure. But this is the feeling of no pressure.” Going weightless made her realize “how rarely we experience an entirely new physical sensation over your whole body, and that was just so different. I couldn’t have really anticipated what it would feel like.”

In fact, she said, it wasn’t until she got back on the ground that she “understood the magic” of the experience. “It was like I had gained this momentary super power that I couldn’t access any more. I felt like I should be able to just launch off the ground and go flying across the hotel lobby.”

I was going to respond to the first comment here, but Brian Swiderski beat me to it. I wish that more of his comments were helpful and civil, like most of his comments on space policy, and fewer (in fact, none) of them on other topics the product of obvious Bush Derangement. Unfortunately, the ratio is the other way around.

However, when commenter “kayawanee” writes that:

While it’s true that there is no further acceleration due to gravity, it’s really inaccurate to say that the skydiver is no longer in free fall once he achieves terminal velocity. Afterall, any object in orbit is considered to be in a perpetual state of freefall, even if (really, especially because) that object is at a constant velocity.

This is clearly (OK, well, not so clearly, or obviously) wrong, which gets back to the previous post on free fall.

Part of the confusion arises from the word “velocity,” and the rest from the special case of a circular orbit.

[Sigh]

The whole reason that I stipulated that the orbit was circular in the previous post was because I didn’t want to open up this new can of worms. I promise that I’ll finish this post, but I have to go stir some chili, and I don’t want people to be misled in the meantime.

[Update a few minutes later]

OK, back from chili stirring (and adding various ingredients to make it more chili-like).

The first issue is simple. Velocity is not speed. Velocity is a vector, and has a directional component. Speed is the scalar of that vector, that represents only the magnitude. Example: going fifty miles per hour east is a vector, going fifty miles per hour is a speed. When one runs in a circular race track at a constant speed (say, 120 mph) the speed is constant, but the vector is continuously changing (with a constant acceleration directed toward the center of the track, otherwise the car wouldn’t be turning). So even if the speed doesn’t change, there is similarly an acceleration in orbit as well.

Here’s where it gets even more complicated. In a non-circular earth orbit, both speed and velocity are changing, because at apogee (the highest point of the orbit), speed is low, but altitude is high, whereas at perigee, it’s the opposite. But in both cases, and all cases in between, the body is in free fall. And the energy of the orbit is constant throughout (thus maintaining Newton’s laws). Free fall simply means that there are no forces acting on the body other than gravity.

In a parabolic aircraft, the only reason that the inhabitants of the airplane are in free fall is because the pilot is flying the trajectory that would apply if there were no atmosphere (that is, he is compensating for the air drag with the thrust of the engines). He is in fact flying an orbit that, if continued, would intersect the earth. In fact, it’s useful to think of the airplane as “flying around” the free fall of the passengers, so that it doesn’t cause an impact with them. He doesn’t continue it, and pulls out after half a minute or so (for subsonic aircraft) for what I hope are obvious reasons.