Let's just say, for the sake of argument, that the equator has a linear eastern velocity of 1,000 mph (actually 1,039). If you release a ball (presumably fired from a cannon) southward from a latitude of 70° north, your ball has an eastern velocity of about 342 mph (cosine of 70° = 0.342). As your ball travels over 45° north, the ground beneath it will have an eastern velocity of about 707 mph (sine or cosine of 45° = 0.707), but your ball will still have its original eastern velocity of 342 mph. The ground beneath your ball will, therefore, be traveling 365 mph eastward faster than the ball. This will make the ball appear to be deflecting to the right, or westward, relative to you.
If your projectile still had enough velocity to cross the equator, the ball would still have that same eastward velocity of 342 mph that it had at launch (neglecting air friction, outside forces, etc.). As it made its way over 45° south latitude, the ground would be moving eastward at 707 mph and the ball eastward still at 342 mph, so the ground would be moving eastward faster than the ball. Relative to you, an observer in the north, the ball would still be deflecting to the right, though that deflection would decrease as it neared the opposite southern latitude. Once the ball made it to the opposite southern latitude, it would then start deflecting to the left (eastward). This is true for any motion crossing the equator. The ball will not start to deflect in the other hemisphere's direction until the ball has passed the latitude opposite from its originating latitude. For instance, if a ball is launched from, say, 35° north latitude towards the equator, it will deflect to the right, cross the equator, continue deflecting to the right (while lessening its deflection as it approached 35° south latitude), and then start deflecting to the left once past 35° south latitude. To a stationary observer in space the ball would appear to travel in a straight line while the earth rotated under it.
If the ball/projectile was launched from the North Pole, it would have no eastward velocity, thus the ball would appear to be travelling to the right (west) equal to the velocity of the ground at that latitude (i.e. 707 mph at 45° North). As it crossed the equator, it would immediately appear to start deflecting to the left (east) and would eventually land at the South Pole, assuming sufficient initial velocity. To a stationary observer in space the projectile would have travelled in a straight line from pole to pole.
Just for clarification: if your ball was launched south from the equator, the ball would have an eastern velocity of 1,000 mph, and as it crossed 45° south latitude, the ground would be moving eastward at 707 mph, while the ball was moving at 1,000 mph, thus appearing to deflect to the left.