Motion & Change
14 concepts in Physics
Motion and change is the study of how objects move through space and time. Students learn to describe motion precisely using concepts like position, displacement, speed, velocity, and acceleration. They work with motion graphs — position vs. time and velocity vs. time — to visualize and analyze movement patterns. This topic covers uniform motion, uniformly accelerated motion, and projectile motion, building a progressively richer picture of how the physical world behaves. The kinematic equations give students powerful tools for predicting where an object will be and how fast it will be moving at any future time. Understanding motion is the starting point for all of mechanics and connects directly to real-world contexts such as driving, athletics, space travel, and the motion of celestial bodies.
Suggested learning path: Start with describing motion qualitatively using everyday examples, then learn to interpret and create motion graphs, and finally apply kinematic equations to solve quantitative problems.
Position
The location of an object relative to a chosen reference point (origin), described using coordinates in a given reference frame.
Displacement
The change in position of an object, measured as the straight-line distance and direction from the starting point to the ending point.
Velocity
The rate of change of position with respect to time, including both magnitude and direction.
Speed
The rate at which an object covers distance over time, calculated as total distance divided by total time, always expressed as a non-negative scalar quantity.
Acceleration
The rate at which an object's velocity changes over time, measured in metres per second squared (m/s²).
Free Fall
Motion under gravity alone, with no air resistance — all objects in free fall accelerate at $g \approx 9.81$ m/s² regardless of mass.
Projectile Motion
Two-dimensional motion under gravity alone, where horizontal velocity is constant and vertical motion is uniformly accelerated — producing a parabolic path.
Circular Motion
Motion of an object along a circular path where the speed may be constant but the velocity is continuously changing direction, requiring a centripetal acceleration.
Reference Frame
A coordinate system attached to a particular observer that is used to describe the positions and motions of objects.
Vectors
Mathematical quantities that possess both a magnitude (size) and a direction, represented graphically as arrows.
Angular Velocity
The rate at which an object rotates about an axis, measured in radians per second, with a direction along the axis.
Average Speed
Average speed is the total distance traveled divided by the total time taken.
Instantaneous Speed
Instantaneous speed is the speed of an object at a particular moment in time.
Relative Velocity
Relative velocity is the velocity of one object as measured from the reference frame of another object.