# Galaxy rotation and Kepler law

by pixel01
Tags: galaxy, kepler, rotation
 P: 10 Galaxy rotation and Kepler law As you know Kepler's laws are true for simple garvitional fields , but talking about galaxies and stars in it , the gravity isn't the same as the gravity between two "very small" objects. To sum up what Tony873004 and WhyIsItSo said , in situations of this kind the force is: -Kr instead of -K/r2! just for Mg use 4$$\pi$$r2$$\rho$$ to get what I'm saying Thanks a lot!