Relative Motion, Distance, and Displacement

"Our study of physics opens with kinematics—the study of motion without considering its causes." "The location of an object at any particular time is its position. More precisely, you need to specify its position relative to a convenient reference frame." "The reference frame is the coordinate system from which the positions of objects are described." "The distance an object moves is the length of the path between its initial position and its final position." "The net change in position of an object is its displacement, or $\Delta\vec{d}$. The Greek letter delta, $\Delta$, means *change in*." "A quantity, such as distance, that has magnitude (i.e., how big or how much) and sometimes a sign ... but does not take into account direction is called a scalar. A quantity, such as displacement, that has both magnitude and direction is called a vector." "$\Delta\vec{d} = \vec{d}_f - \vec{d}_0.$" "A cyclist rides 3 km west and then turns around and rides 2 km east. ... a. Displacement: The rider's displacement is $\Delta\vec{d} = \vec{d}_f - \vec{d}_0 = -1 \text{ km}$. b. Distance: The distance traveled is 3 km + 2 km = 5 km. c. The magnitude of the displacement is 1 km."