klaus wrote:
> Det har været oppe tidligere. Her er et udemærket link:
>
http://www.badastronomy.com/bad/misc/apollohoax.html
>
Da vi alligevel er vi kommet ind på emnet, er der nogen, der gider kigge på
denne adresse?
http://www.apollo-hoax.co.uk/neutral.html
Jeg kom ind på ovenstående adresse, da jeg i sin tid surfede rundt på
web'et efter den omstridte TV-udsendelse. Jeg så straks, at der måtte være
noget galt med formlerne, så jeg sendte nedenstående e-mail til
hjemmesidens forfattere, men indtil dato har jeg ikke fået svar. Kan nogen
fortælle mig, om jeg har ret? Her er teksten af min e-mail:
*************************
Hello
In your page:
http://www.apollo-hoax.co.uk/neutral.html you state that
gravity can be found through the following formula:
g = G*M*m / r^2
I don't know whether I have misunderstood something, but this appears wrong
to me. Firstly, G (the universal gravitation constant) is not
dimension-less. It has the dimension (m^2*N) / kg^2 (N = Newton, i.e. kg*m
/ s^2).
Secondly, your formula does not represent an acceleration (even if you
assume that G is dimension-less). The right formula for gravity is just:
g = G*M / r^2
where g has the correct dimension of an acceleration.
If you now multiplicate this g by the mass "m" of a body (Newton's second
law), you'll obtain the force acting on that body, i.e. the body's weight:
F = G*M*m / r^2
This is actually your original formula. This formula thus represents a
force, and not an acceleration (provided that G has its right dimension, of
course). In our case, if M is the mass of the earth, m the mass of the body
and r the distance from the body to the centre of the earth, then F will be
the weight of that body at the distance r from the centre of the earth.