Re: [Phys-l] Weightlessness in 4 easy steps

[John Denker <jsd@av8n.com>]

On 11/22/2006 01:02 PM, Rick Tarara wrote:

> Also, what exactly changes by .5% over the 35 feet?  I get a laser level to 
> be off by only .00035 inches due to curvature .

Curvature is a second-order effect, and can be neglected in this
situation.

Slope is a first-order effect.  g_N is /angled/ with respect to g_E
by a fraction of a degree.  It's easy to estimate the angle quite
accurately if you model the earth as an ellipsoid;  then you just
need to know the polar radius and equatorial radius.
  http://en.wikipedia.org/wiki/Earth_radius

I get something closer to 0.25% (not 0.5%) at temperate latitudes.

To repeat:  The g_N and g_E vectors differ in magnitude by a fraction
of a percent, and differ in direction by a fraction of a degree, in
the usual terrestrial lab frame.
 -- It is the /angle/ that makes g_N unsuitable for swimming pool
  construction ... and innumerable other real-world applications.
 -- It is the /magnitude/ that makes g_N unsuitable for use in the
  spacecraft frame.