Calculating a planet's mass & gravitational pull

Suicide Junkie · #1 August 21st, 2003, 03:38 PM

You need to multiply by 1000 instead of divide, since there are more meters than kilometers.

Slick · #2 August 21st, 2003, 05:15 PM

DOH! That's pretty much how NASA missed Mars with the Last mission. Or maybe they hit Mars, but they certainly didn't get into orbit as desired. It was a unit conVersion error.

Slick.

Fyron · #3 August 21st, 2003, 11:54 PM

It helps if you set up "conVersion factors" (lame, yes; but still useful). An example:

code:

         / 1000 m \

12 km x  | ------ |  =  12000 m

         \  1 km  /

(those are parenthesis)

dogscoff · #4 August 22nd, 2003, 09:59 AM

Yeah, one of my planned features will be the ability to select different units for input/output. I'll just have to filter all calculations through a "conVersion" function.

Suicide Junkie · #5 August 22nd, 2003, 03:13 PM

Why not just output it in all units simultaneously.
B5 = meters
B7 = B5 * feet/meter
...etc...

dogscoff · #6 August 22nd, 2003, 03:26 PM

That would make it too cluttered. I'm not talking about the spreadsheet any more, I'm currently putting the whole thing into javascript for my webpage.

dogscoff · #7 August 28th, 2003, 01:58 AM

*sigh*

sorry to bother y'all again, but...
Where am I going wrong? I'm trying to work out the calculation needed to derive radius (in km) from a known mass and surface gravity (in metres per second per wotsit):

g=surface gravity, G= gravitational constant, m=mass, r=radius.

g=G*m*(r*1000)^3 - this one works in my excel sheet.
therefore
g/G=m*(r*1000)^3
therefore
(g/G)/m=(r*1000)^3
therefore
cuberoot((g/G)/m)=r*1000
therefore
cuberoot((g/G)/m)/1000=r

Or is that all crud? It's a long time since I studied or used this kind of maths.

Apart from this, the javascript sheet is coming along nicely.