Did you ever use those force carts for a physics lab where a mass dangling over a pully is tied the cart? The cart accelerates when the mass is dropped and the computer plots the distance versus time (from which you can get instantaneous velocities and acceleration).
Based on that idea, it would be neat if you could strap a large human (skier) figurine on top of the cart and fix the body in various positions, then do the same experiment. You could allow passer-by to tinker with the position of the skier and see if their "tuck" was better (or worse) than other peoples'. Maybe do it with the skier naked then put some baggy clothes on him/her?
Ideally, you would have a small enough mass dangling over the edge that the cart/skier would reach terminal velocity quickly, then travel at terminal velocity for a few seconds so that viewers could maybe see a noticable difference in speed.
If your cart computer software is good enough you could show them them graphs of distance, velocity, accelration, etc., but you could just use the terminal vel ocity as the measure of a good tuck.
The math at terminal velocity is cake. The velocity is constant. There is zero net force since the tension in the string pulling the cart is countered by the force of drag due to your skier's position.
To adequately describe the acceleration process, you need some experience with differential equations.