Zero net force means the forces acting on an object balance, so its velocity does not change. With no acceleration, the object maintains both its existing speed and direction. This explains why an object already moving can continue along the same path without requiring a continuing unbalanced force, within the model of constant velocity motion.
Use x = x₀ + vt by identifying the initial position x₀, velocity v, and elapsed time t, then substituting consistent units. The sign of velocity indicates direction relative to the chosen coordinate system. A negative value changes the position accordingly, so the result describes location rather than merely the amount of motion.
A position-time graph represents constant velocity with a straight line whose slope gives the velocity. A steeper slope indicates a greater velocity magnitude, while the slope’s sign indicates direction. On a velocity-time graph, velocity remains constant, so the graph is horizontal. These features help distinguish unchanging motion from motion with acceleration.
Displacement is the change from initial to final position and includes direction, whereas distance describes the total path length. For motion that maintains one direction, their magnitudes can match. The distinction becomes important when interpreting position values and signs, because displacement connects directly to the change represented by the velocity and elapsed time.
First choose a coordinate system and identify the starting position. Next determine the velocity, including its sign, and specify the elapsed time. Substitute these values into x = x₀ + vt, then check the units and interpret the resulting position relative to the chosen origin. This procedure predicts location at a selected time.
This model provides a simple reference for examining more complex motion. Students can first relate position, velocity, direction, and time without accounting for changing velocity. They can then compare the linear position relationship and horizontal velocity graph with cases involving acceleration or changing forces, making the effects of those additional factors easier to identify.