Re: Crit: Ivni, plus noodling

In article <ddfr-3F42FB.00392808072006@xxxxxxxxxxxxxxxxxxxxx>, David Friedman <ddfr@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Water is a lot denser than air, so it is, I would think, a lot easier to
generate a given force using water than air.

Except you haven't considered the entire system: you have to get the water
from somewhere, and then you have water blobs (zero gravity, remember?) flying
around and getting into the works. So "easy" it isn't, when you include the
entire system required. "Generate a given force", yes; "use as a means of
locomotion", no.

The important point is that all animals that use jets to move about use the
fluid that they are immersed in. They also have to pump that fluid through
themselves for respiration. And while the density of water is much higher
than air, so is the resistance to motion through it.

And the momentum transfer of the jet has as much to do with the velocity as
with the mass, or people wouldn't be talking about ion propulsion and such.
To paraphrase: "Pebbles are a lot bigger than ions, so it is, I would think,
a lot easier to generate a given force using pebbles than ions." Might as
well move on up to boulders. But they don't; they just dream up ways to move
the ions faster.

The lungs already have the ability to generate quite high velocities of air,
well over 100 miles per hour IIRC, during a sneeze. A zero-gravity adapted
race could propel itself by air jet quite easily, I would think.

Rich Weyand
Working title "Message Received" complete
WIP: untitled sequel
.

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