Originally Posted by
John C. Ratliff
I have already explained this, but either a stick, a deep pothole (not shallow, but a deep one which would catch and capture the front wheel), or a guard rail can do it. The 15 pound bike shown in the photos above was anchored, into the cyclist/bike that it collided with on the ground. That is very apparent from the photos, as it did not go anywhere after the collision. So it provided an anchored pivot point for the translation of the linear momentum to rotational momentum. Had it not been anchored and was still free-wheeling, it would have continued down the roadway, and there would not be the potential for rotation. But rotation clearly happened, as is shown in the photos.
John, please look into the forces necessary for a body to rotate. Either you are ignoring me or you just don't seem to get it that in order to accelerate a body towards the ground, whether in an arc or even just straight down, there needs to be a force pulling it down. A bike that has simply stopped moving horizontally cannot possibly provide this force. Sure, the bike can stop and the rider can appear to get thrown forward by the bike but that is not what is actually occuring. The cyclist's momentum is carrying them forward and gravity is pushing them down towards the ground. Draw a free body diagram. If you can't point to a force other than gravity (or the bike's weight) pulling down on the rider, you aren't going to appreciably accelerate a human towards the ground.