2
1.1 Motion
Motion is a change in the object‟s position with respect to time. Figure (1.1) describes an object changing
position with time. A complete description of motion requires
A reference from which the position is measured or detected. The tree in Figure (1.1) is a
reference to measure how far or close is the car from the tree
A coordinate system (x, y) of measuring position
According to this description, the motion of any object is considered as
Relative. For example, the motion of the car in Figure (1.1 )is relative to the tree
Usually, the motion is either a long straight line as in Figure (1.1 a&b) or a long a curve (a circle for
example) as shown in Figure (1.2)
(a)
(b)
Figure (1.1) straight line motion . (a) a horizontal motion relative to a tree, and (b) vertical motion relative to earth. In both cases, the
object postion is changing with time. Credit: “Physics for scientists and engineers strategic approach” by Randall D. Knight, PearsonAddison Wesley 2004.