**GRAVITY & CENTRIPETAL FORCE**** ****UNIT 8**

**Dr. John P.Cise, Prof=
. of
Physics, Austin Com. Col.,**

**& **

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**Background: Gravity (F =3D G mM/r^2) provides th=
e force(Centripetal force =3D m v^2/r) needed to keep pl=
anets in
orbit**

**about stars.
The speed of a planet about a=
star
is 2[pi]r/T. T is the period…..the time to make one orbit. The
gravitational**

**constant =
G**** =3D=
6.67 X
10^-11 Nm^2/kg^2. The mass of the sun is ~ 2 X 10^30 kg. In this article a =
star
takes about 10 hrs**

**to**** orbit it’s sun which is sai=
d to
be about the same mass as our sun. Find the distance this 10 hr to orbit the planet is from**

**the center**** of =
it’s
home star? **