From: Marc Afifi (mafifi@redshift.com)
Date: Sat Nov 13 1999 - 08:28:54 PST
Message-ID: <382D919C.5253@redshift.com> Date: Sat, 13 Nov 1999 16:28:54 +0000 From: Marc Afifi <mafifi@redshift.com> Subject: Re: pinhole RE: Centripetal Force at Equator
Paul,
I'm confused. Isn't the centripetal force acting on a 700N person
standing at the equator equal to 700N? The 700N weight is center-seeking
since it is directed radially downward. It is this weight which is the
centripetal force, is it not? Why the 1/300 relation? Perhaps I'm
getting lost in the English.
I calculated a _required_ centripetal force of 2.7N for a 700N person
circling the center of the Earth at the equator. Since the weight
exceeds this 2.7N force, the person stays on the surface. A smaller mass
object would require a smaller centripetal force and would have a
correspondingly smaller weight, but the weight would still be greater
than the required centripetal force and so it would stay on the surface.
I have thought of a couple other questions related to this one.
1. Would the weight of a person at the equator be the same if the Earth
were not rotating? I think the answer to this is yes (ignoring any
reduction in radial distance due to the lack of spin), but that there
would be a normal force exerted *by* the Earth which would be greater if
the Earth were not rotating. Right?
2. Does the fact that the tangential velocity of a person relative to
the Earth is zero at the poles imply a person would have a greater
normal force at the poles than at the equator (assuming a perfectly
spherical Earth)?
-Marc
Paul Doherty wrote:
>
> In simple form
>
> The centripetal force needed on a person standing on the equator is 2.3 N
> because the person weighs 700 N and the centripetal force is about 1/300 of
> the weight.
> an object that weighs 2.3 N would have a centripetal force 1/300 of 2.3 N
> or about 0.006 N.
>
> The force is a function of the mass.
>
> Paul Doherty
>
> Paul "But it is more complicated than that!" Doherty,
> Senior Staff Scientist, The Exploratorium.
> pauld@exploratorium.edu, www.exo.net/~pauld
-- Marc Afifi Physics, Chemistry and Marine Science Pacific Grove High School 615 Sunset Dr. Pacific Grove, CA, 93950 http://www.pghs.org/staff/afifi/d5hp.html(831) 646-6590 ext. 223
Favorite Oakland Raiders Motto: "Just When Baby?"
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