Re: Weightlessness: What is 'Free Fall'?

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

I would define 'free fall' as an acceleration due ONLY to gravity--and
exclusively so.  The common experiences of falling (high dive, bungee jump,
sky-diving) are not strictly 'free-fall' since they include an air
resistance component.  Orbital motion however IS 'free fall' by my
definition.  The orbiting object does move closer to the earth (than it
otherwise would have) due only to the influence of gravity.  However,
because of the velocity at right angles to this accelerated motion, the
object continually tries to move farther away from the earth (or other
planet/star).  It falls 'downwards (towards the planet's center)' due to
gravity just enough to compensate for this 'horizontal' motion's tendency to
move it away from the planet.  Geometrically, the curvature of the planet
surface moves that surface away from the falling object (due to the
'horizontal' motion) at the same rate that the gravitational force is
pulling the object towards the planet--continual 'free fall'.

Now the question as to the meaning of 'weightlessness' in this situation is
a ongoing debate here for which there are two major camps and a few minor
ones.  I won't get into that again.  ;-)

Rick

(See the Newton's Tower animation in the Motion set offered below.)

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
rtarara@saintmarys.edu

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----- Original Message -----
From: "Hasan Fakhruddin" <hfakhrud@GW.BSU.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Monday, May 21, 2001 8:27 AM
Subject: Weightlessness: What is 'Free Fall'?


> I am not too comfortable with the use of the term 'Free Fall' to explain
weightlessness in satellites. If something is falling its height from the
ground is decreasing.
> I believe the use of the term 'Free Fall' is a good escape from a tedious
but accurate explanation for why astonauts feel weightless.
> -Hasan Fakhruddin