Universal Gravitation

Formula- Fg= G m1 x m2/ r2 (Every where else)

Fg=mg (Only on Earth)

To find the force of gravity on Earth is as simple as multiplying the mass by 10. But what if the object is on the moon? What do you do then? You can use the formula above to find the attraction force between two objects.
There is one thing about the G that helps the formal work. G is constant. G is always equal to 6.67 x10(-11). With this always being constant, you can solve for universal gravitation. All you need to know to solve for this is the mass of the two objects and the distance between them.

The equation Fg= G m1 x m2/ r^2 is equal to the equation Fg=mg. Fg=G m1 x m2/ r^2 is used when you don't know what the gravity is. The part of the equation G m1/ r^2 is equal to g in the other equation, that way you can get the force of gravity without having to know to the gravity on the planet, or wherever you are, is. When you calculate what G m1/ r^2, it is equal to g and all you are left with is g(m) which gives you the much simpler equation Fg=mg. This way, you don't have to have the gravity, all you have to have is the constant G which equals 6.67 x10(-11).


1. The mass of Mars is 1.9*(10)27 kg and the mass of the sun is 2.0*(10)30 kg. The distance between the two is 7.7*(10)8 km. Determine the period of Mars' revolution in days.


r= 7.7*(10)11 m
m1= 1.9*(10)27 kg
m2= 2.0*(10)30 kg

m(v)2/r = G*m1*m2/(r)2 (the "m" and "r" cancel out)
(v)2 = (6.67*(10)-11)(2.0*(10)30) / 7.7*(10)11
v = 13162.3

T= 2π(7.7*(10)11) / 13162.3
T= 367568942.1 seconds
367568942.1 seconds = 4254 days = 1 year