The analogy is fun, but where Splash Mountain is concerned, it's not applicable.
"Airtime" that we feel on rides -- typically roller coasters -- comes when the ride vehicle accelerates faster than gravity while traveling up or down an incline. For the force to be pronounced, the change in acceleration or direction needs to happen quickly. Generally, the faster you change direction, the more you'll feel as if you're 'falling out' -- when in reality you're just falling slower than your ride vehicle.
Splash Mountain, as I'm sure you're aware, changes direction at the top of the drops very, very slowly. Thus, you will never feel airtime or leave your seat while on the ride. Your behind is as firmly planted to that bench during the drop as it is when your're slowly passing through the Laughing Place, as it were.
In fact, since Splash Mountain's largest drop falls away at a 45* angle, the speed at which you move downward matches that at which you move forward. You drop 90' while, at the same time, moving forward 90' -- making the forces acting upon your body in any direction pretty well exactly the same as those if you were instead sitting on a bench outside.
