Airbag jackets? Your thoughts? (now other gear questions)

[PDenbigh]

I'll throw my hat in this ring. I can see points to all of these arguments, but my conclusion is that the pivoting of the bike has no effect on the horizontal speed of the rider.

This all takes place within a thousandth of a second:

Phase 1: Rider: When he first hits, his arms bend and he is launched forward for a few millionths of a second. A space forms between him and the bike seat because the crunching of the stronger frame bike causes the middle/back of the bike to slow down at a slightly slower rate. He continues moving at the same speed he was traveling, minus any acceleration (ÔÇ£decelerationÔÇØ) that occurred due to breaking bones, wind resistance, etc. He started decelerating the moment the tire contacts the solid object. ThatÔÇÖs why it takes 180hp to go 140mph in the real world ÔÇô itÔÇÖs equalizing (or exceeding) the other forces pushing against him.

Phase 2: Bike and Catapult: The bottom line is everything happens so quickly that no noticeable positive acceleration would take place. The only thing that happens is that the force vector changes from purely horizontal to some vertical, and thus why he is launched upward.
The length of the bike is the radius of a circle. Take something tied to a string and spin it around your finger. If you spin the string but donÔÇÖt let it coil around your finger, in other words you keep a constant radius, the object doesnÔÇÖt speed up. Now, if you let it coil around your finger, thus decreasing the radius constantly until the object hits your finger, the speed of the end object increases. The only way the rear half of the bike could actually speed up is if the distance between the back and the front decreased. Technically, it does because itÔÇÖs getting smashed, but it is such a small amount that it really wouldnÔÇÖt matter. Because itÔÇÖs such a small amount of horizontal acceleration, it wouldnÔÇÖt be enough to close the horizontal gap formed between the rider and bike in Phase 1. The only way he could be horizontally accelerated by the decreased radius catapult is if the bike again made contact to with him, which it doesnÔÇÖt. He is accelerated vertically by the bike because there is no other vertical force acting on him until the bike start pivoting, and thus no vertical space is formed.