Hello everyone, I am not a physicist nor do I know that much about physics. I do however have a physics question and this seemed like a great place to get an answer. I will present my situation the best I can. I work in the Horizontal Directional Drilling industry. This industry installs pipelines of various sizes underneath obstacles. My question is this these drills are designed on a radius design. Will enter the ground at a determined angle hold a tangential line then curve along a designed radius then back to a tangential length then back to a curve along a designed radius to a determined angle then back to a tangential length then exit the ground. Will then pull the product pipe back through these vertical curves underneath the obstacle. There can also sometimes be horizontal curves designed into these crossings. I hope this part made sense. A pipe is then pulled back through the bore path through the vertical and horizontal curves. My question is this why does the pipe being pulled rotate somewhat, normally less than 150 degrees but it does rotate with no torsional forces being applied. Could someone with some physics knowledge try to explain this to a physics layman. It would be greatly appreciated because several instances have come up in the past where I was not able to explain why this occurred other than "physics I guess." Thanks for any responses.