[IAEP] Gravity for Beginners...

[Bert Freudenberg]

On 28.03.2010, at 06:48, Edward Cherlin wrote:
> 
> On Sat, Mar 27, 2010 at 23:11, Yamandu Ploskonka <yamaplos at gmail.com> wrote:
>> How much lighter is a person in La Paz, Bolivia, than at sea level?
>> This actually was asked by a kid when I was there last time.
>> For practical purposes let's assume La Paz is 3.800 m over sea level
> 
> Fascinating question. The simplest answer is that weight is inversely
> proportional to distance from the center, which we can approximate as
> 40,000 km/pi, or 12,742 km on average. This would give us a difference
> of roughly one part in 5,000 in weight for a difference of 4 parts in
> 10,000 in height.
> 
> However, the distance between surface and center is actually 43 km
> greater at the equator than at the pole, so we have to do some much
> finer calculations to locate sea level at he latitude of La Paz. Then
> we have to decide whether to ask what the weights would be on a
> stationary Earth, or whether we will take rotation into account,
> resulting in apparent decreases in centripetal forces. If we wanted to
> be really finicky, we could take relativity into account also. ^_^

Indeed. My 10 year old son came home recently with the claim that people on mountains live longer. We had some fun introducing relativity, but didn't actually bother to calculate what fraction of a second this would amount to over a lifetime ;)

- Bert -