PH 201 Dr. Cecilia Vogel Lecture 1

OUTLINE  Motion in 1-D  position  displacement  velocity  speed

Motion Along a Line  Like a number line.  Position of object is where it is on the number line  Choose an origin – zero position  Choose a positive direction  For example, position is positive when object is to right of origin

 Displacement is change in position.  final position – initial position:  x = x f - x i Displacement  Object’s displacement is positive if  final position > initial position  object moved in the positive direction Positive displacement: from -3 to -1from 1 to 3 Negative displacement: from 3 to 1from -1 to -3

More on Displacement  Displacement only depends on x f & x i  Doesn’t matter what happens in between  Ex: Object moves from -1 to -3 then to 0.  Overall displacement is 0-(-1) = +1  Displacement may be positive even tho part of the motion is in the negative direction

More on Displacement  Displacement only depends on x f & x i  Doesn’t matter what happens in between  Ex: Object moves from -1 to +3 then to -1.  Overall displacement is (-1)-(-1) = 0  Displacement of zero does not mean the object didn’t move

Instantaneous Speed and velocity  Instantaneous speed is how fast object is going at an instant in time  Always positive  Instantaneous velocity is speed and direction  (instantaneous) speed =the magnitude of the (instantaneous) velocity.

Summary  Positive velocity  Moving forward  Value of position, x, increasing  Slope of x vs. t is positive  Negative velocity  Moving backward  Value of position, x, decreasing  Slope of x vs. t is negative  Zero velocity  Stopped (maybe just for an instant)  Occurs any time motion changes direction  x vs. t graph is horizontal (maybe just for an instant)