People do not often think of trailer balls and maybe they should. A trailer ball is something that is very important if you are going to tow something. The ball is the point where everything attaches and having the right ball makes all the difference in the world.
Why is it a ball at all? The quick answer is that the ball allows the trailer to make smooth turns when, otherwise, it would make very choppy turns or no turns at all. The ball makes the most sense because no other surface or shop would enable the cargo to move as smoothly as a ball would.