frame of reference

a choice of coordinate axes that defines the starting point for measuring any quantity, an essential first step in solving virtually any problem in mechanics

displacement

Delta(x) of an object is defined as its change in position and is given by Delta (x) = x(f) – x(i), where f and i are subscripts, and where x(i) is the coordinate of the initial position of the car and x(f) is the coordinate of the car’s final position. (The indices i and f stand for initial and final, respectively.) SI unit: meter (m)

vector quantity

characterized by having both a magnitude and a direction.

scalar quantity

has magnitude, but no direction

speed

is a scalar quantity having only magnitude

velocity

is a vector quantity, having both magnitude and direction

Average Speed

The average speed of an object over a given time interval is the length of the path it travels divided by the total elapsed time: average speed = path length/elapsed time … SI unit: meter per second (m/s) … This all can be written as v = d/t.

Average Velocity

In general, the average velocity of an object during the time interval Delta T is equal to the slope of the straight line joining the initial and final points on a graph of the object’s position versus time.