1. Describing Motion
2.1

2. Motion occurs when an object changes its position.

3. Motion and Position
Although you did not see the truck move, you know it moved because its position relative to the mailbox changed.
Mark Ransom

4. Movement can be measured only with reference to something that is assumed to be fixed into place – frame of reference
Motion is relative to the observer

7. Distance Displacement
How far an object has moved
SI unit is meter, km, or cm
Distance and direction of an objects change in position

9. Rules for Adding Displacements
Add displacements in the same direction.
Subtract displacements in opposite directions.
Displacements that are not in the same or in opposite directions cannot be directly added.

10. Speed
is the distance an object travels per unit of time.

14. Graphing Motion
The motion of an object over a period of time can be shown on a distance-time graph. For example, the graph below shows the distance traveled by three swimmers during a 30-minute workout. Time is plotted along the horizontal axis of the graph, and the distance traveled is plotted along the vertical axis of the graph.

16. Change in Position
Describing how far and in what direction you moved was an important part of describing your motion.
An object’s displacement is not the same as the total distance that the object traveled. The runner’s displacement is 20 m east of the starting line. However, the total distance the runner traveled is 80 m.

17. His Displacement is only 15 km.

18. Essential Questions How are distance and displacement different?
How is an object’s speed calculated?
What information does a distance-time graph provide?

19. Review Vocabulary
meter: the SI unit of length, abbreviated m

20. New Vocabulary
motion
displacement
speed

21. Assessment 1.
Which of the following do you calculate when you divide the total distance traveled by the total travel time?
average speed A
CORRECT
constant speed B
variable speed C
instantaneous speed D

22. Assessment 2. How is speed defined? acceleration/time
change in velocity/time B
distance/time C
CORRECT
displacement/time D