1. Speed and Acceleration
Measuring motion

2. Measuring Distance Meter – international unit for measuring distance.
1 mm
= 50 m

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

4. Units for speed
Depends, but will always be a distance unit / a time unit
Ex. Cars: mi./h
Jets: km/h
Snails: cm/s
Falling objects: m/s

5. Calculating speed S = d/t
If I travel 100 kilometer in one hour then I have a speed of…
100 km/h
If I travel 1 meter in 1 second then I have a speed of….
1 m/s
S = d/t

6. Average speed Speed is usually NOT CONSTANT
Ex. Cars stop and go regularly
Runners go slower uphill than downhill
Average speed = total distance traveled/total time it took.

7. Calculating Average Speed
It took me 1 hour to go 40 km on the highway. Then it took me 2 more hours to go 20 km using the streets.
Total Distance:
40 km + 20 km = 60 km
Total Time:
1 h + 2 h = 3 hr
Avg. Speed:
total d/total t = 60 km/3 h = 20 km/h

8. I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes
I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed?
100 m/min
2000 m/min
10 m/min
200 m/min
20 m/min 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

9. 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

10. Question
I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed?
Total Dist. = 1000 m m = 2000 m
Total Time = 3 min + 7 min = 10 min
Ave speed = total dist/total time =
2000m/10 min = 200 m/min

11. Question What is the difference between speed and velocity?
Speed is just distance/time. Velocity includes direction as well.
For the next few slides, we will refer to speed, but if you add a direction, this works for velocity as well…
Speed is just distance/time. Velocity includes direction as well.

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

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

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

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

16. 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

17. 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

18. What does the slope of this distance vs
What does the slope of this distance vs. time graph show you about the motion of an object?
Acceleration
Average Acceleration
Speed
Changes in Velocity 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

19. 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

20. Acceleration
Chapter

21. Try to define the word “acceleration”…
Actual definition is…any change in VELOCITY

22. Acceleration is a change in velocity.
So…Is it a vector or a scalar quantity?
VECTOR
It must include a direction (like velocity)
This also means that you can change acceleration by changing what?
Speed or Direction

23. This object is accelerating every 15 minutes
How would you describe the motion shown in the distance – time graph below?
This object is accelerating every 15 minutes
This object is changing velocity every 15 minutes
This object is moving at a constant speed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

24. Does travel at a constant speed mean you are not accelerating?
Remember that you can change velocity by changing direction, thus CHANGING ACCELERATION!

25. When a ferris wheel goes up and around, what about its passengers is changing?
Speed
Velocity
Acceleration
None of the above 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

26. So let me get this straight…
Constant Speed means –
Something travels the same distance in each time interval
Constant Velocity means-
Something travels the same distance, in the same direction in each time interval
So what about constant acceleration?
Distance heading south in km

27. Constant Acceleration
The velocity changes by the same amt over each time interval. (figure 11, p 329)
Ex- centripetal acceleration
As the earth goes around the sun, it travels at a constant speed
BUT since it is going in a circle, it’s velocity is changing AT A CONSTANT RATE…therefore…
CONSTANT ACCELERATION!

28. Which of the following lines shows constant velocity?B 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

29. Which of the following lines shows constant accelerationB C D 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

30. Acceleration Acceleration – the rate at which velocity changes
So if the slope of a velocity time graph is straight, acceleration is constant

31. 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

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

33. Calculating Acceleration
If an object is moving in a straight line…
∆V= change in velocity
(Final Velocity – Initial Velocity) (m/s)
A= acceleration
∆ T= time (s)
(final time- initial time)
A ∆T ∆V
So what are the units of acceleration?
If A= V/T…
Acceleration is in m/s2

34. Calculating Acceleration
Acceleration = (Vf-Vi) t
Let’s look at the picture below…what is this car’s avg 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

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