Equations of motion Key concepts
Kinematics describes, dynamics explains
Kinematic equations describe how position, Velocity, acceleration, and time relate. They do not tell you why acceleration exists. For the cause, use Newton’s Laws of Motion.
Acceleration is change in velocity
Acceleration can mean speeding up, slowing down, or changing direction. In one dimension, signs matter: if velocity and acceleration have opposite signs, the object is slowing down.
Displacement is not distance
The SUVAT variable means displacement, not total path length. If an object returns to its start point, even though distance travelled is not zero.
Graph meanings
- Slope of position-time graph = velocity.
- Slope of velocity-time graph = acceleration.
- Area under velocity-time graph = displacement.
- Area under acceleration-time graph = change in velocity.
Assumption to check
The standard equations in Equations of motion Equations and definitions require constant acceleration. If acceleration is not constant, use the derivative/integral definitions instead.
Next: Equations of motion Examples and Equations of motion Common pitfalls.
Average velocity shortcut
With constant acceleration, velocity changes linearly, so average velocity is simply . That is why works. If acceleration is not constant, that average may be wrong; use the area under the velocity-time graph instead.