Originally Posted by justanotherskipro
Sorry to spend so much time on my soapbox but I say with respect this idea, even good skiers and inteligent men like Ghost have fallen for this myth about the VB being more than it is.
You are making an erroneous assumption Jasp. I do not think the VB is more than it is. It is pretty simple 3-D physics and geometry, but perhaps I did not explain my self well enough. Vaulting is great at accelerating your body up. The virtual bump cannot accelerate your body up. Rebound is nothing compared to vaulting. All fine and good so far?
Now let's get to the important part.
Newton's first law, a body will continue to travel in uniform motion unless it is acted upon by an external force.
Newton's second law, a body will accelerate in the direction of the net forces applied on that body, and it's acceleration will be equal to the forces divided by the mass (using the right units).
A skier travelling horizontally will continue to travel horizontally unless he is forced from his horizontal path. Gravity is the only force that will accelerate our skier down, and he can only loose elevation with an acceleration of 9.81 m/s/s, or less if he pushes up against the ground/snow.
A skier travelling at 100 kph 90 degrees to the fall line is travelling horizontally, with zero vertical velocity, nada, zip. The fastest he can loose altitude is given by his current vertical velocity (0) and acceleration due to gravity -9.81 m/s/s. His position (relative to his current position at 0 m elevation ) even if he did not push up at all against the slope would be y = -0.5(9.81) t^2 m, where t is time in seconds. He can not lose altitude any quicker than that.
Now let's say our skier is skiing on a 35 degree slope, and he got perpendicular to the fall line by pulling off an amazing 2g turn (at 100 kph); he is headed for the trees, but he is not worried because he thinks he can pull off another 2 g turn back down the slope (he can't). That 2 g turn would, if he were able to pull it off, give him a turn radius of slightly more than 26 m. He would travel along an arc of that radius, increasing his distance along that arc at 27.7 m/s and increasing his horizontal distance in the direction of the fall line's projection on the horizontal plane at the rate of x= 26.2 * (1-cosine(theta)) where theta is the angular distance around the arc in radians. His trajectory can be plotted as elevation versus horizontal distance corresponding to the fall line direction. A 35 degree slope can also be plotted. Here they both are:
You can see the problem, If he were to turn in the required arc to miss those trees, falling as fast as possible, his skis would leave the ground. What happens when you skis start to leave the ground\snow? You stop turning. You know this free skiing as balancing on the edge of traction turning down the hill as fast as you CAN. You do not experience being airborne from the virtual jump, because you can't turn hard enough without your skis on the snow. Our poor skier looses traction trying to make that arc and ends up turning too wide and into the trees, just like a motorcycle rider who doesn't know how to lean his bike in a corner.
I'm sure you have pushed yourself out from a wall to skim over some rocks when skiing really steep terrain. If you can get enough of a turn accomplished before your skis leave the ground you will be airborne.
A lot of variables: lower slope = don't have to worry about edges leaving the ground the ground. Ski slow = don't have to worry about edges leaving the ground. Turn more gradually = don't leave the ground.