We can observe changes in the watershed. Changes are governed by physical laws. A. Forces can change the state of motion of an object. A force is a push or pull. Examples include gravity, which pulls toward the center of the earth, and friction, which always opposes motion.
Vectors are useful for describing forces and their effects.
The effective gravitational force on earth materials may depend upon the steepness of the slope on which the materials are located. Balance between gravitational forces and frictional forces determine the stability of sloping surfaces. Effects of forces are described by Newton s Laws of Motion. Velocity is the rate of change of position. Acceleration of an object will be proportional to the net force acting on the object and inversely proportional to the mass of the object.