1. Speed and Velocity
Chapter 9.2
Page 342

2. Objectives for 9.2
Know how to calculate the speed and average speed of an object.
Know the difference between instantaneous speed and average speed
Know how to describe an object’s velocity by stating the speed and direction.
Know how to describe a change in velocity in terms of speed or direction or both.
Know how to answer questions about speed and distance from a graph.

3. Speed= Distance Time Calculating Speed
Speed is defined as “the distance the object traveled in one unit of time”.
Speed= Distance
Time
Example: If a car travels 180 km in 2 hours, then the car is traveling 90 km/h.
180 km = 90 km
2 h h

4. Constant Speed
If the speed of an object does not change, then it is traveling at a constant speed.
Ex: A boat traveling across the ocean.
If you know the distance an object travels in a given amount of time, you can use the formula for speed to determine the object’s constant speed.
Speed= Distance
Time

5. Average Speed Total Time
Most objects do not move at constant speeds.
Example: When driving to Los Angeles, you may have to slow down for traffic, stop and get fuel, etc.
You can find an object’s average speed by dividing the total distance traveled by the total time.
Average Speed= Total Distance
Total Time
Example: A Cyclist travels 32 km during the first 2 hours and 13 km during the next hour.
Total Distance: 32+13=45km
Total Time= 2+1= 3 h Average Speed: 45km =15km/h 3h

6. Speed The formula for calculating speed is: Speed = Distance Time
Speed is defined as the rate at which an object travels OR the distance an object travels for a specific unit of time

7. Common Expressions of Speed
45 miles per hour is the same as
45 miles or 45 mi/h
hour
100 meters per second is the same as
100 meters or 100 m/s
second

8. Notice the Units!!!! miles = distance = SPEED hour time
meters = distance = SPEED
second time

9. Calculating Speed
Joe rides his bike a distance of 300 meters in 30 seconds. What is his speed?
Distance = 300 meters
Time = 30 seconds
Speed = Distance = 300 meters = 10 m/s
Time seconds

10. Calculating Speed
Jill can jog 2 miles in 0.5 hours. What is her speed?
A frog can jump 10 meters in 50 seconds. What is its speed?

11. Instantaneous Speed
Instantaneous speed is the rate at which an object is traveling at a given instant in time
When would it be important to know your instantaneous speed?

12. Velocity
Velocity is a vector quantity. Vectors show both magnitude and direction.
Velocity= speed in a given direction
Therefore, if you know the velocity at which an object is moving, then you know the object’s speed, as well as its direction.
Example: A storm’s velocity is 25 km/h in an eastward direction.

13. Graphing Speed

14. Graphing Speed
You can use distance-versus-time graphs to interpret motion.

15. Graphing Speed