1. Describing Motion
Chapter 3

2. Objectives Quiz 2 Draw and use motion diagrams to describe motion
Use a particle model to represent a moving object
Choose coordinate systems for motion problems
Differentiate between scalar and vector quantities

3. Objectives Quiz 2
Define a displacement vector and determine a time interval
Recognize how the chosen coordinate system affects the signs of vectors quantities
Define velocity and acceleration operationally
Relate the direction and magnitude of velocity and acceleration vectors to the motion of objects
Create pictorial and physical models for solving motion problems

4. Motion and Particle Model Diagrams
Motion Diagram
A series of images of a moving object after equal time periods
If images are equal distance, constant speed
If images get closer, slowing down
If images get farther, speeding up
Particle Model
Using a dot instead of actual object
Physics teachers are notorious bad artists 

5. Motion Diagrams
What can you determine about the motion of the bird? The runner? The car?

6. Particle Diagram

7. Coordinate Systems
Indicate direction

8. Time Intervals ∆t

10. Use a particle model or motion
Runner moving at constant speed
Runner starting from rest and picking up speed
Car that starts from rest, speeds up to a constant speed, and then slows to a stop

11. Use a particle model or motion
A wheel turning at constant speed

12. Coordinate Systems Choosing what equals zero
Origin
In high jump, ground is zero feet, and vertical is positive
In long jump, line is zero feet, and horizontal is positive
Usually chosen to make math easier

13. Scalar and Vector Quantities
are quantities which are fully described by a magnitude (or numerical value) alone
Vectors
are quantities which are fully described by both a magnitude and a direction.

14. Scalar or Vector? 1) Elevation 22,000 ft 2) 60 mph 3) 5 miles North
4) 20 degrees Celsius
5) calories
6) 10 m/s East

15. Scalar Vector Answers
Vector
Scalar

16. Speed A non-directional rate at which something is covered.
Distance over Time
V=d/t

17. Instantaneous Speed
Speed at any instant

18. Total distance divided by total time= Average Speed
Quantity divided by time=Rate

19. Speed Related Terms Velocity (v)- Speed in a given direction
This changes if either speed or direction change
Acceleration (a)-
Change in velocity/time interval

20. Positive and Negative Acceleration

21. Describe my motion A) SOOOOOOOOOOOOOOOOOOE
B) S O O O O O O O O O O O O O O E
C) E O O O O O O O O O O O O O O S
D) S O O O O O O E
E) S O O O O O O E
F) E O O O O O O S
G) SOO O O O O O O O E

22. Questions about acceleration
A car is slowing down, is the acceleration positive or negative?
A car driving down the highway maintains a constant speed around a curve. Does the car accelerate?

23. Scalar Vector Distance and Speed are Scalar Quantities
How much ground an object has covered
How fast the object is moving without regards to direction
Displacement and Velocity are Vector Quantities
It is the object's overall change in position.
How fast the object moved in the right direction

24. Adding Vectors Line up vector arrows from tip to tail
Add magnitudes to find resultant vector
Reminder: Some are negative

25. Displacement
∆d = df - di

26. Displacement
A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North.
Distance?
Displacement?

27. Displacement Distance Covered = 12 meters Displacement = 0 meters
South Cancels North
East Cancels West

28. More Practice Distance the skier covered? Avg speed of skier?
Avg velocity of skier?

29. More Practice
Distance = 420 m
Displacement = 140 m to the right

30. Follow up
How do the answers change if the origin is the skier’s location at 1 min?
How do the answers change if left is positive?

31. More Practice Distance the Coach moved?
Avg velocity of coach for 10 min?

32. Crab Walk
The slowest animal ever discovered was a crab found in the red sea. It traveled an average speed of 5.7 km/yr. How many seconds would it take this crab to sprint the 100 m dash?

33. Pictorial Models
A problem solving strategy, just a sketch of what is going on
Read the problem and sketch the situation
May need multiple separate sketches
Establish coordinate system if needed
Reread problem and make a list of variables and assign a symbol to them
Determine known and unknown quantities

34. Draw a model
A dragster starting from rest accelerates at 49 meters per second squared. How fast is it going when it has traveled 325 meters?

35. Draw a model
A speeding car is traveling at a constant speed of 30 m/s when it passes a stopped police car. The police car accelerates at 7 m/s/s. How fast will it be going when it catches up with the speeding car?

36. Draw a model
A car is traveling 20 m/s when the driver sees a chidl standing in the road. He takes 0.8s to react, then steps on the brakes and accelerates at -7 m/s/s. How far does the car go before it stops?

37. Draw a model
You throw a ball downward from a window at a speed of 2.0 m/s. The ball accelerates at 9.8 m/s/s. How fast is the ball moving when it hits the sidewalk?
How does the model change if the ball is thrown up at -2.0 m/s?