physics question about pull ups

John Cochrane wrote:
No, Gary means it. In theory, we can gain a lot by strong pull ups and
pushovers in thermal entries and exits. In fact, in theory, you can
stay up when there is only sink. You push to strong negative g's in
the sink, then strong positive gs when you are out of the sink. Huh?
Think of a basketball; your hand is sink and the ground is still air.
When you push hard negative g's in the sink, the glider exits the sink
with more airspeed than it entered, just like the basketball as it
hits your hand. The opposite happens when you pull hard for the first
second or two after entering lift.

I _think_ I get what you are saying: you basically propose extracting the
kinetic energy that is available due to the different fluid speeds. It
doesn't matter which direction the fluid streams flow - merely that one
part of the fluid is moving relative to another part and you can move your
aircraft from one to the other.

We're so used to getting energy out of upward fluid flows that we overlook
the fact that in a fundamental sense it doesn't matter (to a first
approximation) which direction the stream is going.

So what you all seem to be saying is that there is energy available for
extraction in wind shear, sinks, and thermals. If the whole mass of fluid
is moving then you are out of luck because you need a difference in fluid
speeds - with the exception that upward flows always make energy available
due to conversion of the fluid kinetic energy to gravitational potential
energy. (Hence the "first approximation" caveat.)

Is all that about right?