1. Physical Science 11.3 Speed and Velocity

2. Speed and Velocity Speed
The ratio of the distance an object moves to the amount of time the object moves
Units
Measured in m/s or km/hr
Average Speed
Speed over the entire duration of a trip
Instantaneous Speed
Speed during a particular instant of time

3. Formula: Speed = Distance (d) Time (t) v = d / t
Average Speed
Formula: Speed = Distance (d) Time (t) v = d / t

4. Solving problems!!
Ask yourself: What is the problem wanting me to solve for?
Find and write the correct formula
Substitute what your know into your formula
Solve equation (Don’t forget units!!)

5. Average Speed
Example #1: You travel 350 meters in 120 seconds. What is your average speed? 2.92 m/s Example #2: An object travels 100 meters in 4 seconds. What is the objects average speed? 25 m/s

6. Average Speed
Example #3: A train is traveling 10 m/s in 240 seconds. How far did the train travel? 2,400 meters Example #4: How long did it take an object traveling at 25 m/s to go 2,000 meters? 80 seconds

7. How are instantaneous speed and average speed different?
Instantaneous speed is measured at a particular instant in time
Average speed is computed for the entire duration of a trip

8. Graphing Motion The slope of a line on a distance-time graph is speed
The steeper the slope, the faster you are traveling
The flatter the slope, the slower you are traveling

9. Graphing Motion Example #1
Each line (A and B) represent the motion of two objects. Which object is moving faster? Explain.

10. Graphing Motion Example #2
Which car has a faster speed: The big car or small car? Explain

11. Graphing Motion Example #3
Using this graph, what is the average speed of the Big Car and the average speed of the small car?

12. Different Motion Graph Examples

13. What is the slope of a distance vs. time graph?
Speed!!!

14. Velocity
Velocity:
A description of both speed and direction of motion.
Velocity is a vector
Velocity has the same formula as speed, except we add a direction

15. Velocity
Example #1 An automobile travels 2,500 m north along a straight road for 200 seconds. Calculate the velocity. Example #2 A jet liner passes over St. Louis travelling at 625 m/s, heading straight towards Kansas City, which is 235 meters away. How much time elapses before the aircraft passes over Kansas City if it maintains a constant velocity?

16. Looking at Graphs

17. Distance vs. Time Graphs
Time always runs horizontally (the x-axis).
The arrow shows the direction of time. The further to the right, the longer time from the start.
Distance runs vertically (the y-axis).
The higher up the graph we go, the further we are from the start.

18. What is the speed of the airplane?
Speed = 1,200 km / 6 hrs
= 200 km/hr
Denver
Phoenix

19. Different Slopes Speed = d / t = 0 km/2 hr = 0 km/hr Speed = d / t

20. What is the average speed?
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
12 km
6 hours

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

22. Each line represents a journey from home to the office.
Here is another time-distance graph with 2 journeys represented on the same graph.
Each line represents a journey from home to the office.
The red line is Dave’s journey.
The green line is Mike’s journey.
1000 m
500 m 5 10 15
1500 m
How long after Dave does Mike leave?
3 seconds
Distance
After how many seconds does Mike catch up?
7 seconds
How far from home are they then meet?
500 meters
What is the speed of each person?
Dave (Red): 70 m/s
Mike (Green): 125 m/s
Time (sec)

23. 11.3 Assessment Questions
Question #1 How are speed and velocity different? Velocity is speed with direction Question #2 What shows the speed on a distance-time graph? The slope

24. 11.3 Assessment Questions
Question #3 How can two or more velocities be combined? Vector addition

25. 11.3 Assessment Questions
Question #4 What is going on in each section of the following distance-time graph?