1. Chapter 9 Section 2 Speed & Velocity

2. What is physics?
Physics is a description of our Universe Position is the foundation of physics. Our Universe is interesting because positions change.

3. Speed Speed (R) – Rate at which an object is moving.
speed = distance / time
R = d/t
Like distance, speed does not depend on direction.

4. Speed A car drives 100 meters in 5 seconds.
What is the car’s average speed?
s = d/t
s = (100 m) / (5 s) = 20 m/s
100 m
5 s
4 s
1 s
2 s
3 s

5. Speed
A rocket is traveling at 10 km/s. How long does it take the rocket to travel 30 km?

6. Speed
A racecar is traveling at 85.0 m/s. How far does the car travel in 30.0 s?

7. 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.

8. Average speed

9. 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
Ave. Speed:
total d/total t = 60 km/3 h = 20 km/h

10. Velocity Velocity (v) – speed with direction.
velocity = displacement / time
v = x / t

11. Pulling It All Together
Back to our ant explorer!
Distance traveled: 7 cm
Displacement: +3 cm
Average speed: (7 cm) / (5 s) = 1.4 cm/s
Average velocity: (+3 cm) / (5 s) = +0.6 cm/s cm 1 2 3 4 5 6 7 8 9 10 + -
5 s
4 s
1 s
2 s
3 s

12. Question
I travelled 25 km in 10 minutes. How many meters have I travelled?
A) m
B) m
C) .025 m
D) 2.5 m
25 km * 1000m/km = m

13. Question
I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed?
A) 100 m/min
B) 2000 m/min
C) 10 m/min
D) 200 m/min
E) 20 m/min
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 = D

14. 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.

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

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

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

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

19. 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

20. 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

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