space elevator physics

I don't have access to USENET right now, so I can't get immediate consultation with other people in the physics community, but I think that Steven Den Beste's analysis of space elevator physics is omitting some facts which IMHO ameliorate the pendulum effect he describes. He writes:

Thinking of this as an elevator in a building is the wrong model, because a building is stiff. The right way to think of it is as a weight hanging from a string. At my altitude with my orbital velocity, such a weight hangs "down". At the altitude of the proposed counterweight, it hangs "up". (Actually, it's "down" too by definition. But it's the direction that we on the earth think of as "up".) But in every other way it's very similar. What you're talking about is the world's largest pendulum.
So you got your elevator crawling up the kevlar ribbon, and like the elevator in the building, it is not only forcing itself and its passengers "up", but also "sideways". To reach the classic geosynchronous orbital altitude, you not only have to pick up a lot of altitude, but also several kilometers per second of lateral velocity.
What will happen is that as the elevator rises, it's also going to be forced to the side:
When an elevator climbs this ribbon, it's going to make the counterweight start to swing back and forth, with a very long period. (It's impossible to calculate the period without knowing the mass of the counterweight and its altitude and the mass per kilometer of the ribbon, but it's going to be on the order of hours or days.) When the elevator goes back down, it will cause lateral force in the opposite direction, but that may not necessarily be helpful; it all depends on when it goes and how long it takes to reach the ground and which side the counterweight has swung to. It's actually possible for a descending elevator to increase the swing. It doesn't necessarily automatically decrease it.

If I understand the space elevator concept, it is designed to be built at the equator. The centrifugal force (not centripetal) applies to the eleator structure itself, which would keep it rigid. Also, the mass of the elevator is so huge that the mass of any cargo and the cabs that traverse the elevator is negligible in comparison, so they won't have much effect. Fundamentally, the space elevator is a transformer, turning the Earth's rotational energy into kinetic energy.

I may have a BS in physics, but my MS is in Medical Physics and MRI theory, so I am NOT an expert on dynamics. So I may be grossly wrong.

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