Quantities of Motion

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QUANTITIES OF MOTION

Distance (d) [m] - Scalar

Distance between 2 points is the length of the shortest path (straight line) between these points.

Distance travelled is the total length of the actual path travelled when going from one point to another.

Displacement (d) [m] - Vector

Displacement of one point from another is the distance from the first point in a specified direction.

In 1D, displacement can be taken as negative or positive depending on direction from a reference point.

Speed (v) [m/s] - Scalar

The rate of change of distance, with respect to time.

Instantaneous speed is the speed at any given point in time.

Average speed considers the total distance travelled and time taken, not changes in speed during time interval.

Velocity (v) [m/s] - Vector

Rate of change of distance in a particular direction. Rate of change of displacement.

Average velocity considers total change in displacement and time taken.

Direction of velocity will always be the same as direction of change in displacement.

Acceleration (a) [m/s2] - Vector

Rate of change of velocity with respect to time.

Direction of acceleration is always same as direction of change in velocity.

Change in velocity -> acceleration. Speeding up, slowing down, changing direction or any combination.

In 1D, when object is speeding up, direction of acceleration is same as direction of velocity. When slowing down, direction of acceleration is opposite to direction of velocity.

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EQUATIONS OF MOTION

v = d/t -> can only be used when acceleration is zero and velocity is constant/average.

These equations can only be used when acceleration is uniform - same magnitude and same direction.