Motion - Terminology

Scalar A scalar quantity is a quantity that requires only a magnitude (size) and appropriate units for its full description. Examples – distance, speed, time

Vector Quantity A quantity that requires a magnitude (size), appropriate units, and a direction for its complete description. Examples – Displacement, velocity, acceleration, force

Position The separation between an object and a reference point in a particular direction.

Position-Time Graph Graph of an object’s motion that shows how its position depends on clock reading, or time.

Distance The separation between two points. This is a scalar quantity.

Displacement A change in position in a particular direction. Because direction matters, displacement is a vector quantity.

Speed Rate of distance traveled to time interval. Because speed is distance over time, speed is a scalar quantity and direction is not important.

Velocity The ratio of the change in position to time interval over which the change takes place. Velocity is a measure of displacement over time and since displacement is a vector quantity, velocity is also a vector quantity.

Velocity-time graph A plot of velocity of an object as a function of time.

Acceleration Change in velocity divided by time interval over which it occurred. Or…rate of change in velocity. In IB Physics, a “rate of change” refers to a time rate of change unless otherwise indicated. Since change in velocity is a vector quantity, acceleration is also a vector quantity.