1. Representing Motion

2. Chapter 2 Representing Motion
We will begin by studying motion in a straight line; we will eventually learn about motion in 2 dimensions (projectiles and circular motion) and vibrating objects.

3. 2.1 Picturing Motion
Motion diagram – a series of images showing the positions of a moving object at equal time intervals
Particle model – simplified version of a motion diagram using dots to represent the object in motion.

4. Motion Diagram: shows position of a moving object
at equal time intervals
Particle Diagram:
Simplified version of the motion diagram

5. Motion Diagram of Bird
Bird’s Eye view
Wing Tip View

6. Motion Diagram of a Car

7. The Big Race

8. “how much ground an object has covered”
Mechanics -
Study of motion
Kinematics -
Description of motion
Dynamics -
Causes of motion
Terms:
distance
displacement
velocity
speed
Description of motion – how fast, how long of a trip, how far
words, diagrams, numbers, graphs & equations
Walk 4 m S (right in 218) 8 m E, 4 m N, and 8 m W
Total distance = 24 m
acceleration
distance -
“how much ground an object has
covered”

9. 2.2 Where and When
Coordinate system – system used to describe motion that gives the zero point location of the variable being studied and the direction in which the values of the variable increase. 2 4 6 8 10

10. Can an object have a negative position?
Yes

11. Vectors vector – quantity that has magnitude and direction
magnitude = size
• Examples: velocity, acceleration, force
• Arrows are used to represent vectors
• The sum of two or more vectors is called the resultant

12. Scalars
Have magnitude only
Examples: mass, temperature, time

13. Scalar quantity
any quantity that only has magnitude
( amount)
Examples:
scalar
vector
displacement
distance
velocity
acceleration
time
temperature
mass
volume
speed
density

14. Time Interval t t = tf – ti t is used to represent time
t is the change between two times
t = tf – ti
Usually, initial time is zero.

15. Displacement d d = df – di d is used to represent position
d is the change between two positions
d = df – di
Usually, initial position is zero.

16. displacement includes direction
change in position
2m S
3m S
5 m S
displacement includes direction
(vector quantity)
Any quantity that
includes direction to
be completely described
Displacement – term familiar with, but not its true meaning
Example: using windows as a reference point, I am 2 m S of the window. This is my original position- I move 3 m S or to the right. My new position is 5 m S.

17. displacement is not the same as distance
4m S
1 m S
3m N
distance =
7 m
displacement =
1m S

18. Other directions:
5 m up
+5m
+ 3m
3 m right
4 m left
2 m down
-2m
-4m
Signs may also me used +
Right , up, North
Left, down,South -

19. Δd = df - di displacement = change in position
= final position – initial position
Δd = df - di 10 20 30 40 50 60 cm
xi=20 cm
xf=55 cm
Δd = df - di
Δd = 55.00cm – cm
or 35 cm right

20. 10 20 30 40 50 60 cm
xf=20 cm
xi=45 cm
or 25 cm left

21. Only the initial position and the final position is important.
A bug travels from the 45 cm mark to the 60cm and then to the 5 cm and ends at the 20 cm mark.

22. Vertical displacement
Dy is used instead
of Dx 10 20 30 40 50 60 yf
= +40 cm
or 40 cm up yi

23. Final displacement may also be found by adding displacements
(with direction included) 2 3 1
Bug travels 30 cm right,
then 20 cm left and
finally 10 cm right.
+30 cm + (-20cm) cm
= cm
or 20 cm right

24. 2.3 Position-Time Graphs Plot time data on horizontal (x) axis
Plot position data on vertical (y) axis
Pg 39 #9, 11
Pg 41 #14- 18

25. (go to “describing motion with graphs” ppt)