Changing the level of effort you exert during an activity is an example of adjusting which training principle

Yes i have used it before

Rub your hands together twice as long as washing your hands? or make sure to in between your fingers. or wipe ur hands off with a paper towel when done.

Pretty much everywhere: walking requires friction, driving around curves, steering a car with the steering wheel, starting fire with a stick, objects moving along a conveyer belt.