Motion - Chico Unified School District

Speed and Velocity
Chapter 9.2
Page 342
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.
Calculating Speed
Speed is defined as “the distance the
object traveled in one unit of time”.
• Speed= Distance
Example: If a car travels 180 km in 2
hours, then the car is traveling 90 km/h.
180 km
90 km
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
Average Speed
• 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
The formula for calculating speed is:
Speed =
Speed is defined as the rate at which an
object travels OR the distance an object
travels for a specific unit of time
Common Expressions of Speed
45 miles per hour is the same as
45 miles or 45
100 meters per second is the same as
100 meters or 100 m/s
Notice the Units!!!!
meters =
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
30 seconds
Calculating Speed
1. Jill can jog 2 miles in 0.5 hours. What is
her speed?
2. A frog can jump 10 meters in 50
seconds. What is its speed?
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?
• 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.
Graphing Speed
Graphing Speed
• You can use distance-versus-time graphs
to interpret motion.
Graphing Speed

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