it is for a shared computer usually so that you don't need to type your password
Friction is important for all sports. Without it it becomes really hard to accelerate or deaccelerate. For example a 100m sprinter. It would be great for him if there wasnt any air resistance...
If you are stuck with metal for example you can heat it
Both are acceptable, depending on context. For example: Fishing bait is useful to fisherman. Fishing bait is useful for catching fish.
young man? 27! mike