1. Distance, Direction and Position
Chapter 12

2. Chapter Twelve: Distance Direction and Position
12.2 Speed
12.3 Graphs of Motion
California 8th Grade Science Standards Addressed
1. The velocity of an object is the rate of change of its position. As a basis for understanding this concept:
Students know position is defined in relation to some choice of a standard reference point and a set of reference directions.
Students know that average speed is the total distance traveled divided by the total time elapsed and that the speed of an object along the path traveled can vary.
Students know how to solve problems involving distance, time, and average speed.
Students know the velocity of an object must be described by specifying both the direction and speed of the object
Students know changes in velocity may be due to changes in speed, direction, or both
Students know how to interpret graphs of position versus time and graphs of speed versus time for motion in a single direction

3. Chapter Twelve: Distance, Time, and Speed
12.1 Distance, Time, and Position
12.2 Speed
12.3 Graphs of Motion

4. Investigation 12B
Speed
Which ramp is fastest?

5. 12.2 Speed
We use the variable speed to describe how quickly something moves.
Saying a race car, runner, or plane is “fast” is not enough to accurately describe its speed scientifically.

6. 12.2 Speed
The speed of a bicycle is the distance it travels divided by the time it takes.

7. 12.2 Average Speed
The speed found by dividing the total distance by the total time is the average speed.

8. Average Speed

9. 12.2 Constant speed
Constant means “does not change” so constant speed is speed that does not change.
How do we know the speed of the bike is constant?

10. 12.2 Units for speed
Since speed is a ratio of distance over time, the units for speed are distance units over time units.

11. 12.2 Relationships between distance, speed and time
An equation can be used to calculate speed, distance, or time if two of the three values are known.

13. Forms of the Speed Equation

14. 12.2 Calculating Speed
To use a formula, remember that the words or letters stand for values that the variables have.
You can think of each letter as a box that will eventually hold a number.