This isn't for homework or anything, I was just trying to figure this out for fun. So what I tried to do to find the mass of the Earth was this: Fg=G(m1m2)/r^2 10kg(9.8)=6.67x10^-11(10kg)(m2)/40,678,884 9.8=6.67x10^-11(m2)/40,678,884 398,653,063=6.67x10^-11(m2) 5.976x10^18=m2 I looked up the mass afterwards and it's apparently 5.97x10^24. So I was off by about a million kilograms... Where did I mess up? Or is my whole process just completely screwed up? Don't be too harsh on me, I just finished learning about forces in school, and had to look up the law of universal gravitation on wikipedia... PS. Sorry if I posted this in the wrong category (I tried the homework category, but when I saw the template I felt like I was definitely in the wrong place).