1. Describing Motion
The Equations…

2. What is the difference between distance and displacement?
Distance: How far something travels
Displacement: How far something travels in a given direction

3. SCALAR vs VECTOR Quantities
Scalars are quantities which are fully described by a magnitude alone.
Vectors are quantities which are fully described by both a magnitude and a direction.
Distance traveled = AC + CB + BC = 400 m.
Displacement = 200 m right of A

4. A skier travels from A to B then to C then to D.
What distance does she travel?
420 m
What is her displacement at D from A?
140 m right of A

5. V (m/s) ½ bh = ½ vt ½(4 m/s)(5s) = 10m t (s) ½(-4 m/s)(5s) = -10m
Example 1. Consider a body that accelerates from 4m/s to -4m/s in 10s.
a. Plot the body's velocity vs. clock reading graph.
b. How far did the body move during the interval?
c. Did the body move during the interval? If so, how? Describe Qualitatively.
½ bh = ½ vt
4 m/s
½(4 m/s)(5s) = 10m
t (s)
V (m/s)
½(-4 m/s)(5s) = -10m
10m-10m = 0 m ?
-4 m/s

6. PROBLEM SOLVING GUIDELINES
• Make a list of given quantities (Data)
• Convert units if needed
• Make a sketch if necessary
• Identify what is to be determined
• Always solve the equation for the unknown
• Be consistent with units
• Check that the answer seems reasonable
• Physics problems take practice –
the more you do the easier it will be!

7. Example 2: A runner makes one lap around a 200 m track in a time of 25 s. What is the runner's average speed?
Givens:
Base formula/rule:
Answer:
Work:
Diagrams:
d = 200 m
t = 25 s
8 m/s
Sav = d t
Unknown: Sav
Sav = d t m s
= 8 m/s

8. Units: m/s2 ACCELERATION
 Acceleration is the rate of change of velocity. The change in velocity ΔV is the final velocity Vf minus the initial velocity Vo.
Units: m/s2

9. Find the speed at the end of 5.0 s
Example 3: An object starts from rest with a constant acceleration of 8.0 m/s2 along a straight line.
Find the speed at the end of 5.0 s
Givens:
Base formula/rule:
Answer:
Work:
Diagrams:
Vo = 0 m/s
a = 8.0 m/s2
t = 5.0 s
Vf = 40 m/s
Vf = ?
Vf = 0m/s + (8.0m/s2)(5.0s)
Vf = 40 m/s

10. Example 4: A truck's speed increases uniformly from 15. 0 km/h to 60
Example 4: A truck's speed increases uniformly from 15.0 km/h to 60.0 km/h in 20.0 s. Determine the acceleration.
Givens:
Base formula/rule:
Answer:
Work:
Diagrams:
vo = 15.0 km/h
= 4.17 m/s
vf = 60.0 km/h
= 16.7 m/s
t = 20 s
= m/s2
a = ?
m/s s
= m/s2

11. Example 5: A bus moving at a speed of 20
Example 5: A bus moving at a speed of 20.0 m/s begins to slow at a constant rate of 3.00 m/s2. How long before it stops?
Givens:
Base formula/rule:
Answer:
Work:
Diagrams:
t = 6.67 s
Vo = 20 m/s
Vf = 0 m/s
a = - 3 m/s/s
t = Vf – Vo a
t =?
t = 0 – 20 m/s
-3 m/s2
t = 6.67 s

12. Do you remember? Answer the following in your notes,
A. You walk exactly 250 steps North, turn around and walk exactly 400 steps South. How far are you from your starting point? Is this distance or displacement?
B. A small car rolling along a horizontal surface of 3.25 meters in a time of 1.35 seconds. What is the average speed of the car? (Include all your steps)

13. d = vt d d EQUATIONS FOR MOTION UNDER CONSTANT SPEED:
CONSTANT ACCELERATION: d d

14. Example 5: A bus moving at a speed of 20
Example 5: A bus moving at a speed of 20.0 m/s begins to slow at a constant rate of 3.00 m/s2.
B) How far did the bus travel during this 6.67 sec?
Givens:
Base formula/rule:
Answer:
Work:
Diagrams: d
Vo = 20 m/s
Vf = ? m/s
t = 6.67 s
a = -3 m/s/s
d = ?
d = 66.7 m d
d =(20m/s)(6.67s) + ½(-3m/s2)(6.67s)2
d = 66.7 m

15. Pictures were taken every second of a set of spheres moving from left to right. The diagram below shows the location of the sphere when each photograph was taken. The total time intervals shown vary among the spheres. All displacements are in meters.
Rank these sphere on the basis of the greatest average velocity over the first three seconds. Give the highest rank to the sphere with the greatest average velocity and the lowest rank to the sphere with the least average velocity

16. Examine the first three seconds of motion
Examine the first three seconds of motion. Sphere A travels 6m, B travels 3m, C travels 2m, D travels 9m, E travels 7m and F travels 9m.
The ranking would be F>D=E>A>B>C

17. Describing Motion Class/Homework: This Way & That Way I
Motion Problem #1-6