1. Physics Principles and Problems
Representing Motion
Chapter 2
Physics Principles and Problems
Zitzewitz, Elliot, Haase, Harper, Herzog, Nelson, Nelson, Schuler and Zorn
McGraw Hill, 2005

2. Motion An object whose position changes over time.
Motion Diagram - shows the positions of a moving object at successive times.

3. Visualizing Motion
Coordinate System - shows the location of the zero point (origin) and direction of an object in motion.
Arrows can be utilized to show an objects position and distance traveled.

4. Vectors and Scalars
Vectors are quantities that have both magnitude (size) and direction.
0 15m
Scalars are quantities that are numbers without direction
4C, 5m, 39s, 22m/s

5. Resultant Vectors
Vector that represents the sum of two or more vectors.
Based upon their direction some vectors can be negative.

6. Time Intervals and Displacement
Time Interval - equals the final time (tf) minus the initial time (ti)
∆ t = tf - ti
Displacement - equals the final position (df) minus the initial position (di)
∆ d = df - di

7. Position - Time Graphs
By plotting the time (t) and position (d) data of a particular object a position-time graph can be generated.
Remember that d represents that object’s instantaneous position.
t d
30 0
55 0

8. Average Velocity v = ∆d / ∆t = df - di / tf - ti
Defined as the change in position divided by the time during which the change occurred.
v = ∆d / ∆t = df - di / tf - ti
Average velocity is represented by the slope of the line in a position-time graph

9. Speed vs. Velocity
Speed is how fast an object in moving. It is a scalar quantity and therefore can never be negative.
Velocity is speed with direction. It is a vector quantity and therefore can be negative.
Instantaneous velocity is the speed and direction of an object at a particular instant.

10. Equation of Motion for Average Velocity
An object’s position is equal to the average velocity multiplied by time plus the initial position.
d = vt + di
Use algebra and the equation v = d / t to solve for any of the variables.