Re: [Phys-L] apparent weight

[Jeffrey Schnick <JSchnick@Anselm.Edu>]

> -----Original Message-----
> From: Phys-l [mailto:phys-l-bounces@www.phys-l.org] On Behalf Of John
> Denker
> Sent: Thursday, December 11, 2014 4:40 PM
> To: Phys-L@Phys-L.org
> Subject: Re: [Phys-L] apparent weight
>
> I never thought this was tricky until I started doing some googling.  Wow, are
> there a bunch of wrong answers out there.
>
>
> I haven't reviewed them super-carefully, but the following look correct on
> first impression:
>   http://www.lhup.edu/~DSimanek/scenario/tides.htm
>   http://tidesandcurrents.noaa.gov/restles3.html
>
> Here is a key point:
>
> The centrifugal field due to the rotation of the earth plays no role in
> producing the tides.  It gives rise to the ellipsoidal (non spherical) shape of
> the earth, but that is a background constant.  The tides exist relative to that.
>
> Therefore you can save yourself a lot of trouble by analyzing the case of a
> non-spinning earth.  The tides will be the same.  Not spinning once a day, not
> even spinning once a month or once a year, but fixed in orientation.  The
> stars never rise or set.
This is indeed a key point.  I got it wrong in my analysis. The centrifugal field is already taken into account in the weight of the person standing on a scale on the equator of an earth-like object that is spinning at the same rate as the earth but is not in orbit about a star.