Uniform and Non-uniform Motion
Uniform motion: constant speed in a straight line. Non-uniform motion: changing speed and/or direction. These ideas lead to graphs and equations of motion.
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Uniform and Non-uniform Motion
Toggle: constant speed vs changing speed. Position–time graph below.
Uniform motion
In uniform motion, the object covers equal distances in equal intervals of time. For motion in a straight line with constant velocity, the position–time graph is a straight line and the velocity–time graph is a horizontal line. No acceleration is present in the direction of motion.
Non-uniform motion
In non-uniform motion, the object does not cover equal distances in equal intervals of time—either the speed changes or the direction changes (or both). The velocity–time graph is not horizontal; the slope gives the acceleration. Most real motions (e.g. a car in traffic, a ball in free fall) are non-uniform.
Why it matters
Uniform motion is the simplest case and is used to introduce displacement, velocity, and graphs. Non-uniform motion requires the concept of acceleration and leads to the equations of motion for uniformly accelerated motion, which is a very common approximation (e.g. free fall, braking).
Why do we often treat free fall as uniformly accelerated motion even though air resistance affects real falling objects?