Describing Motion Around Us Chapter 4 Vocabulary

Fundamental vocabulary terms and concepts regarding linear motion, displacement, velocity, acceleration, and graphical analysis from Chapter 4.

Linear motion

Motion in a straight line, which is the simplest kind of motion.

Position

The distance and direction of an object with respect to a fixed reference point at any given instant of time.

Reference point

A specified fixed point used to describe the position of an object.

Motion

The state of an object if its position with respect to the reference point changes with time.

Rest

The state of an object if its position with respect to the reference point does not change with time.

Origin ʻOʼ

The point on a coordinate line representing the reference point from which distances are measured.

Displacement

The net change in the position of an object between two given instants of time, requiring both numerical value and direction.

Magnitude

The numerical value (with units) of a physical quantity.

Scalars

Physical quantities which can be specified by just their numerical value.

Vectors

Physical quantities which require specifying both the direction and magnitude.

Instant of time

A single reading of a clock at one given point of time.

Time interval

The time duration between two instants of time, or between two readings of a clock.

Average speed

The total distance travelled divided by the time interval during which the distance was covered.

Uniform motion in a straight line

Motion in which an object travels equal distances in equal intervals of time for all possible choices of time intervals.

Non-uniform motion in a straight line

Motion in which an object travels unequal distances in equal intervals of time.

Average velocity

The ratio of displacement to the time interval in which the change in position occurs, describing how fast and in what direction position changes.

Rate of change

The ratio of the change in one physical quantity to the corresponding change in time.

Instantaneous velocity

The velocity of an object at one particular instant of time, occurring when the time interval becomes infinitesimally small.

Average acceleration

The change in velocity divided by the time interval over which the change occurs; calculated as $\frac{v - u}{t_2 - t_1}$.

SI unit of average acceleration

Metres per second squared, represented as $\text{m s}^{-2}$ or $\text{m/s}^2$.

Acceleration due to gravitational force ($g$)

The constant vertical acceleration of a falling object, equal to $9.8\,\text{m s}^{-2}$.

Instantaneous acceleration

The acceleration of an object at a specific instant of time.

Slope of a line

The steepness of a line on a graph that provides the rate of change of the Y-axis quantity with respect to the X-axis quantity.

Area enclosed by the velocity-time graph and the time axis

A geometric value equal to the displacement of the object in a desired time interval.