1. Acceleration Key Concepts
What kind of motion does acceleration refer to?
How is acceleration calculated?
What graphs can be used to analyze the motion of an accelerating object?

2. Key Terms
Acceleration

3. What is Acceleration? Everyday language – the process of speeding up
Scientific definition – the rate at which velocity changes
A change in velocity can be a change in speed or direction – or both
Therefore acceleration refers to increasing speed, decreasing speed or changing directions

4. Increasing Speed Examples: A car moving from a stopped position
A car speeding up to pass another car
A person coasting down a hill on a bicycle

5. Decreasing Speed Negative acceleration
Examples
Softball landing in fielder’s mitt
A car stopping at a red light
Water skier when the boat stops pulling

6. Changing Direction Examples
A car following a bend in the road at constant speed
A car changing lanes on a highway
A softball as it changes directions when it is hit
Circular motion such as a Ferris wheel is continuous acceleration although the speed may not change

7. Calculating Acceleration
If an object is not changing direction you can calculate its acceleration as the rate at which its speed changes
Formula:
Acceleration = Final speed – initial speed
Time

8. Units for Acceleration
If speed is measured in meters/second and time is measured in seconds, the SI unit for acceleration is m/s/s or m/s2 If speed is measured in km/hr and time is measured in hrs, the SI unit for acceleration is km/hr/hr or km/hr2

9. Acceleration Example Look at the plane on p. 24 and 25
The plane’s initial speed is 0m/s
The plane’s final speed is 40 m/s
The time it took for the plane to speed up to 40m/s was 5 s.
Acceleration = final speed – initial speed
Time
=40m/s-0m/s =40m/s =8m/s2
5s s

10. Graphing Acceleration
speed vs time graphs and distance vs time graphs can be used to analyze the motion of an accelerating object

11. Speed vs Time Graphs
Upward slanting line shows that speed is increasing
Downward slanting line shows that speed is decreasing
Straight line shows that acceleration is constant
Find acceleration by calculating the slope of the line – slope = Rise
Run

12. Speed vs Time Graph

13. Distance vs Time Graph Represents the motion of an accelerating object
Curved line means an object is accelerating
Shows that during each second the object travels a further distance
Also shows that each second the speed is greater than the second before

14. Distance vs Time graph

15. Distance vs time graph