text: what is meant by corriolis principle?   christina is wrong. when you drop something, it is already rotating along with the earth, and continues to do so as it falls, for there is nothing to stop it.  in fact, the real coriolis effect depends on the fact that an object dropped, or thrown, or shot out of a gun, is rotating along with the earth. consider this. a spot on the equator is rotating eastward at about 1,000 miles per hour. places north of that are rotating eastward slower than that. places near the north pole are rotating eastward very slowly. a circle around the north pole having a circumfrence of 24 miles is rotating eastward at 1 mile per hour.  if you position a gun on the equator, the bullet contained therein is travelling eastward at 1,000 miles per hour, along with the gun. if you shoot the gun northward, the bullet wlil travel over land that is travelling eastward slower than 1,000 miles per hour. the bullet, however, will continue to travel eastward at 1,000 miles per hour because there is nothing to stop it. the bullet will appear to have an eastward force applied, but there is no such force.