Re: What's wrong with this?

From: George Murphy <>
Date: Tue Jun 22 2004 - 07:39:42 EDT

----- Original Message -----
From: "Glenn Morton" <>
To: "'George Murphy'" <>; "'Ted Davis'"
<>; <>
Sent: Monday, June 21, 2004 10:46 PM
Subject: RE: What's wrong with this?

> > Ted & Glenn -
> > Not exactly. Objects in free fall _are_ weightless
> > because in a coordinate frame moving with them the
> > gravitational acceleration has been transformed away locally.
> > It doesn't matter how high you are - you're weightless
> > (except for the effects of air resistance) when you jump off
> > the high dive. Astronauts train for weightlessness - or at
> > least they used to - in planes that are in free fall (though
> > perhaps moving upward & horizontally - on a parabolic path)
> > for a fraction of a minute.
> You are generalizing when we were speaking of the precise case you laid
> out about the plane. We weren't speaking of high diving. We were talking
> about a plane going quite fast, which would have a significant
> frictional force. So, I will say that you are doing a bit of a bait and
> switch here. Agreed that a diver is weightless (I used to do acrobatic
> diving until I was 35 when I broke my leg in 4 places after landing on
> the diving board after a beautiful (weightless) gainer).

    You may be right that the drag at those speeds & altitudes is
significant enough that it wouldn't have been weightless for much of the
flight & the report would have been wrong on that count too. (OTOH near
apogee both speed & atmospheric density would be low so drag would have been
very slight.) But the implication that weightlessness had something to do
with distance from the earth was wrong in any case.
    I don't know if this thread has accomplished anything else but at least
we've discovered another of your talents!

Received on Tue Jun 22 08:08:18 2004

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