Motion - Chico Unified School District

Report
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
Time
•
Example: If a car travels 180 km in 2
hours, then the car is traveling 90 km/h.
180 km
2h
=
90 km
h
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
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
3h
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
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
Notice the Units!!!!
miles
hour
=
distance
time
=
SPEED
meters =
second
distance
time
=
SPEED
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
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
• 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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