3. Acceleration  What is acceleration?  If you’re traveling in a car at a constant speed of 50 mph, are you accelerating?  No, you’re not.  Acceleration is the rate of change of velocity.

4. Acceleration  In order for acceleration to occur, velocity MUST be changing.  Remember, velocity is the speed and direction an object is traveling.  In order for acceleration to occur, something must be speeding up, slowing down or changing direction.

5. Types of Acceleration  If a car is speeding up, does it have positive or negative acceleration?  Positive  If a car is slowing down, does it have positive or negative acceleration?  Negative  If a car is traveling at a constant speed of 50 mph, does it have positive or negative acceleration?  Neither! It’s acceleration is 0. (Technically, zero is a positive number, but we won’t get into that.)

6. Speed/Time Graphs  This graph shows speed increasing over time.  Would the acceleration be positive or negative?  This graph shows positive acceleration. Time Speed

7. Slopes of Speed/Time Graphs  When the line on a graph goes upward from left to right, it is said to have a positive slope.  A positive slope on a speed/time graph shows positive acceleration. Time Speed

8. Speed/Time Graphs  What does this graph show?  As time is going by, how is the speed changing?  If the speed is decreasing over time, is the acceleration positive or negative?  This speed/time graph shows negative acceleration. Time Speed

9. Slopes of Speed/Time Graphs  When the line on a graph goes downward from left to right, it is said to have a negative slope.  A negative slope on a speed/time graph shows a negative acceleration. Time Speed

10. Speed/Time Graphs  What does this graph show?  As time is going by, the speed is staying the same.  Is the object accelerating if the speed stays the same?  No! This graph shows no acceleration. It is possible for an object to have speed with no acceleration. Time Speed

11. Slopes of Speed/Time Graphs  When the line on a graph is perfectly horizontal, it’s slope is said to be zero.  A zero slope on a speed/time graph shows zero acceleration. Time Speed

12. Calculating Acceleration  Acceleration is often given with the units m/s ²  With these units, acceleration is telling us how many m/s faster (or slower) an object is moving each second.  The equation for acceleration is… Acceleration = (final velocity – initial velocity) / time

13. Calculating Acceleration  A car is sitting a red light when the light turns green. The car goes. After 10 seconds the car is traveling at a speed of 20 m/s. What is the car’s acceleration?  A = (20 – 0) / 10 = 2 m/s²  That means each second that passed the car was traveling 2 m/s faster than the previous second.  This is an example of calculating positive acceleration.

14. Calculating Acceleration  A car is traveling at a speed of 50 m/s. The driver notices a cop car and slows to a speed of 30 m/s over a period of 5 seconds. What is the car’s acceleration?  A = (30 – 50)/ 5 = -4 m/s²

15. Reading a Speed/Time Graph  Give an explanation for what might be occurring if a car’s speed/time graph looked like this… Time Speed

16. Reading a Speed/Time Graph  Here is another speed/time graph.  The car accelerates twice. Which portions of the graph show the car accelerating? Time Speed When does the car have a greater acceleration? How do you know? The steeper the slope the greater the acceleration.

17. Reading a Speed/Time Graph  ‘Read’ the following speed/time graph. Be as descriptive as possible. Time Speed