With out friction we would not be able to experience the true joy of skiing. Ff equals the force created by the friction, and Fn equals the force perpendicular to the direction of travel. In skiing acceleration and deceleration can be both fun and a killer. Your acceleration is what allows you to gain speed as you go down the hill. It is that speed you gain from your acceleration that allows you to do things like jump cliffs, table tops, etc.
Deceleration is the biggest killer in skiing.
The tree Sunny Bono hit caused a extremely rapid deceleration and the forces involved in that deceleration are what caused his fatal injuries. In skiing your acceleration is caused by earths gravity. However you can experience acceleration and deceleration in many other things including driving your car. The basic defintion of acceleration is a change of velocity over a given time. Without gravity there would be no skiing.