The Traffic Accident Reconstruction Origin -ARnews-

Re: Snowmobile speed response to archive thread

Gene K. Baxter ([email protected])
Sat, 31 Oct 1998 03:43:40 -0500 (EST)

Bruno, you were on the right "track" with the conservation of angular momentum but you got off the "track" in your last sentence when you stated that "the track's rotational inertia stays about the same." As the snowmobile leaves the ramp, there is a sudden decrease in load on the track (assuming the throttle is held constant) so the track speed will increase. Therefore, the rotational (angular) inertia of the track system will also increase (say, clockwise, per your viewer on the right). By conservation of angular momentum (since there are no significant external torques on an airborne snowmobile), the "counterclockwise" rotational inertia of the snomobile body must also increase. And, when that happens, guess what? The rear end of the snowmobile will drop. That was the original question, why does the rear end drop? In fact, you can easily demonstrate this concept by hanging a motorcycle in your garage (on a single line) and then "gun" the throttle. Its the same effect. Ther
e are no "external" forces on the "system" so the angular momentum is conserved and the rotational inertia of the wheel will increase in one direction while the body of the motorcycle will rotate in the opposite direction.
Gene K. Baxter
[email protected]

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