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Its been a while since I've done any physics, I'm working on some orbital programs. I'm using this formula

$\mu = MG$

where $M$ is the mass of the body and $G$ is the gravitational constant.

The value that I find for earth is $398600$ or so

However $G$ is defined with $10^{-11}$ exponent and the mass of the earth is defined as $5$ with a $10^{24}$ exponent. The units of kilograms are same but it seems like it should have 13 decimal places, not 5.

What am I missing?

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  • $\begingroup$ sorry, the Greek mu is the way I've seen it referenced. It could be double ghgh = Mass * GravitationalContant $\endgroup$
    – John Mott
    Aug 24, 2015 at 0:06

1 Answer 1

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You need to be careful with the units. On the Wikipedia page which gives the gravitational parameter of the Earth as $398,600$, the units are km$^3$s$^{-2}$, so this is $3.986E14$ m$^3$s$^{-2}$ in agreement with your figures for $G$ and the mass of the earth in SI units.

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  • $\begingroup$ Thank you, I was focused on the kg unit and missed the conversion of meters to kilometers. $\endgroup$
    – John Mott
    Aug 24, 2015 at 2:34

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