6.1. Universal Law of Gravity http://www.ck12.org
where G is the Gravitational constant:
G= 6. 67300 × 10 −^11 m^3 kg−^1 s−^2Here is an illustration of this law for two objects, for instance the earth and the sun:
Gravity on the Earth’s Surface
On the surface of a planet — such as earth — therin formula [3] is very close to the radius of the planet, since a
planet’s center of mass is — usually — at its center. It also does not vary by much: for instance, the earth’s radius is
about 6,000 km, while the heights we consider for this book are on the order of at most a few kilometers — so we
can say that for objects near the surface of the earth, therin formula [3] is constant and equal to the earth’s radius.
This allows us to say that gravity is more or less constant on the surface of the earth. Here’s an illustration:
For any object a heighthabove the surface of the earth, the force of gravity may be expressed as:
F~G=Gmearthmob j
(rearth+h)^2Now we make the approximation that
rearth+h≈rearth