First Law of Motion: Inertia — An object will continue its current motion or lack thereof until some net force causes its speed or direction of movement to change.

Second Law of Motion: Force — The acceleration of an object is directly proportional to net force acting on it. Expressed as force equals mass times acceleration.

Third Law of Motion: Action/Reaction — For every action, there is an equal and opposite reaction.

Related terms in Physics Terms for Fly Casting: Speed, Velocity, Acceleration, Positive Acceleration, Negative Acceleration / Deceleration, Constant Acceleration

From the FFI Fly Casting Definitions (2025 Edition), reproduced with attribution to Fly Fishers International.