1. Speed & Velocity
Measuring Motion

2. AGENDA Bell Work Notes on Speed Hot Wheelin’ Speed Lab Exit Pass
HW Collected
Notes on Speed
Hot Wheelin’ Speed Lab
Exit Pass
Homework
Announcements

3. Bell Work
Imagine cars driving on a freeway, how would you describe their movement? Use as many details or description as you can. What are some examples?

4. OBJECTIVES: Relate speed to distance and time.
Standard 3.2: Explain and describe what is acceleration. Write the equation (formula) for speed. Solve problems using the equation for speed.
Relate speed to distance and time.
Solve problems using speed, time, and distance.
Create distance-time graphs.
Create speed-time graphs.

5. S = d/t Calculating Speed:
Speed (S) = distance traveled (d) ÷ the amount of time it took (t).
S = d/t

6. Manipulating the Speed Formula:
What if you wanted to find out speed (HOW FAST)? D
Since D is above the T, we know we have to divide OR S T D T

7. Manipulating the Speed Formula:
What if you wanted to find out the distance (HOW FAR)? D
Since S is next to the T, we know we have to multiply OR S T
S X T

8. Manipulating the Speed Formula:
What if you wanted to find out the time (HOW LONG)? D
HOW LONG – does not mean how far… DO NOT FORGET!
Since D is above the S, we know we have to divide OR S T D S

9. Don’t Forget About Your Units:
meters (m)
meters per second OR
m/s S T
seconds (s)

10. S = d/t Calculating speed
If I travel 100 kilometer in 2 hours then I have a speed of…
100÷2 = 50 km/h
If my speed is 50 m/s in 5 seconds then I have a distance of….
50 X 5 = 250 m

11. Velocity Velocity – the SPEED and DIRECTION of an object. Example:
An airplane moving North at 500 mph
A missile moving towards you at 200 m/s

12. Question What is the difference between speed and velocity?
Speed is just distance/time. Velocity includes direction as well.
Speed is just distance/time. Velocity includes direction as well.

13. Graphing Speed: Distance vs. Time Graphs
Denver
Phoenix

14. Graphing Speed: Distance vs. Time Graphs
Speed = Slope = Rise/Run
Rise

15. Graphing Speed: Distance vs. Time Graphs
Speed = Slope = Rise/Run
Rise=?
600 km
3 h

16. Graphing Speed: Distance vs. Time Graphs
Speed = Slope = Rise/Run
Rise=?
600 m
3 minutes
Rise/Run = 600 km/3 hr
= 200 km/hr

17. Different Slopes Slope = Rise/Run = 0 km/1 hr = 0 km/hr Rise = 2 km
Run = 1 hr
Rise = 0 km
Run = 1 hr
Slope = Rise/Run
= 2 km/1 hr
= 2 km/hr
Rise = 1 km
Run = 1 hr
Slope = Rise/Run
= 1 km/1 hr
= 1 km/hr

18. Average Speed = Total distance/Total time = 12 km/6 hr
Question
Below is a distance vs. time graph of my position during a race. What was my AVERAGE speed for the entire race?
Average Speed = Total distance/Total time = 12 km/6 hr
= 2 km/hr
Rise = 12 km
Run = 6 hr

19. Question
What does the slope of a distance vs. time graph show you about the motion of an object?
It tells you the SPEED

20. Question
Below is a distance vs. time graph for 3 runners. Who is the fastest?
Leroy is the fastest. He completed the race in 3 hours

21. Speed-time graphs 1) Speeding Up 4) Slowing down80 60 40 20
4) Slowing down
Speed
m/s
3) Speeding up, slower than first increase (slope is less steep)
2) Same (constant) Speed
T/s

22. Distance-Time (Position) Graphs
1) Constant Speed 80 60 40 20
4) Going back, but at constant speed
Distance (m)
3) Speeding up, but slower
2) Stopped
T/s

23. Acceleration Acceleration = speeding up
How much faster or how much slower you are going with a direction
Acceleration – the rate at which velocity changes
Can be an:
Increase in speed
Decrease in speed
Change in direction
DECELERATION

24. Types of acceleration Increasing speed Decreasing speed
Example: Car speeds up at green light
Decreasing speed
Example: Car slows down at stop light
Changing Direction
Example: Car takes turn (can be at constant speed)
screeeeech
DECELERATION

25. Question
How can a car be accelerating if its speed is a constant 65 km/h?
If it is changing directions it is accelerating

26. Calculating Acceleration
If an object is moving in a straight line
Final Velocity – Initial Velocity
ACCELERATION =
Time
A = Vf-Vi t
Units of acceleration:
m/s2 or m/s/s
m/h/h or m/h2

27. Calculating Acceleration
0 s
1 s
2 s
3 s
4 s
0 m/s
4 m/s
8 m/s
12 m/s
16 m/s

28. Question
A skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration?

29. Acceleration – What is it exactly?
Time (s)
Speed (m/s) 1 2 3 4 5 6 7 8
What is happening to your speed if you have an acceleration of 5 m/s2? 5 10 15

30. Acceleration – What is it exactly?
Time (s)
Speed (m/s) 1 2 3 4 5 6 7 8
What is happening to your speed if your speed is 20 m/s but have an acceleration of 10 m/s2? 20 10
-10
-20
-30
Are you slowing down?
No, you’re just going the other way.

31. Acceleration Graphs
1) Increasing acceleration (speed getting faster by certain amount each second) 80 60 40 20
4) Deceleration
Acceleration
m/s/s
3) Increasing acceleration
2) Constant Acceleration (speed is still increasing)
T/s

32. Acceleration – What is it exactly?
What if we know the acceleration, how do we find the final speed, the start speed, or even how long it took (time)?
t = Vf - Vi
How long? (Time) a
Vf= at + Vi
Final Speed (Vf)
Vi= Vf - at
Initial Speed (Vi)

33. Now your turn: Try a couple of these problems: a = Vf - Vi
Acceleration t
t = Vf - Vi
How long? (Time) a
Vf= at + Vi
Final Speed (Vf)
Vi= Vf - at
Initial Speed (Vi)