The speed of an in-line skater is usually described in meters per second. The speed of a car is usually described in kilometers per hour.
11.2 Speed and Velocity
How are instantaneous speed and average speed different?
Speed
Average speed is computed for the entire duration of a trip, and instantaneous speed is measured at a particular instant.
11.2 Speed and Velocity
Speed is the ratio of the distance an object moves to the amount of time the object moves.
The SI unit of speed is meters per second (m/s).
Two ways to express the speed of an object are average speed and instantaneous speed.
Speed
11.2 Speed and Velocity
Average Speed
Sometimes it is useful to know how fast something moves for an entire trip, even though its speed may change during the trip.
Average speed, is the total distance traveled, d, divided by the time, t, it takes to travel that distance.
Speed
11.2 Speed and Velocity
Calculating Average Speed
While traveling on vacation, you measure the times and distances traveled. You travel 35 kilometers in 0.4 hour, followed by 53 kilometers in 0.6 hour. What is your average speed?
Speed
11.2 Speed and Velocity
Read and Understand
What information are you given?
Speed
11.2 Speed and Velocity
Read and Understand
What information are you given?
Total Distance (d) = 35 km + 53 km = 88 km
Total Time (t) = 0.4 h + 0.6 h = 1.0 h
Speed
11.2 Speed and Velocity
Plan and Solve
What unknown are you trying to calculate?��
What formula contains the given quantities and the unknown?�
Replace each variable with its known value.
Speed
11.2 Speed and Velocity
Plan and Solve
What unknown are you trying to calculate?��
What formula contains the given quantities and the unknown?�
Replace each variable with its known value.
Speed
11.2 Speed and Velocity
Look Back and Check
Is your answer reasonable?�
Speed
11.2 Speed and Velocity
Look Back and Check
Is your answer reasonable?�
Yes, 88 km/h is a typical highway speed.
Speed
11.2 Speed and Velocity
1. A person jogs 4.0 kilometers in 32 minutes, then 2.0 kilometers in 22 minutes, and finally 1.0 kilometer in 16 minutes. What is the jogger’s average speed in kilometers per minute? �
Speed
11.2 Speed and Velocity
1. A person jogs 4.0 kilometers in 32 minutes, then 2.0 kilometers in 22 minutes, and finally 1.0 kilometer in 16 minutes. What is the jogger’s average speed in kilometers per minute? �
Answer:
Speed
11.2 Speed and Velocity
2. A train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed?
Speed
11.2 Speed and Velocity
2. A train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed? �
Answer:
Speed
11.2 Speed and Velocity
Instantaneous Speed
Sometimes you need to know how fast you are going at a particular moment.
Instantaneous speed, v, is the rate at which an object is moving at a given moment in time.
Speed
11.2 Speed and Velocity
The speedometer in a car measures the car’s instantaneous speed.
Note the scale markings are given both in km/h and miles per hour, mph.
Speed
11.2 Speed and Velocity
How can you find the speed from a distance-time graph?
Graphing Motion
The slope of a line on a distance-time graph is speed.
11.2 Speed and Velocity
A distance-time graph is a good way to describe motion.
Slope is the change in the vertical axis value divided by the change in the horizontal axis value.
A steeper slope on a distance-time graph indicates a higher speed.
Graphing Motion
11.2 Speed and Velocity
Graphing Motion
11.2 Speed and Velocity
Graphing Motion
11.2 Speed and Velocity
Graphing Motion
11.2 Speed and Velocity
How are speed and velocity different?
Velocity
Velocity is a description of both speed and direction of motion. Velocity is a vector.
11.2 Speed and Velocity
Sometimes knowing only the speed of an object isn’t enough. You also need to know the direction of the object’s motion.
Together, the speed and direction in which an object is moving are called velocity.
Velocity
11.2 Speed and Velocity
A cheetah’s speed may be as fast as 90 km/h. To describe the cheetah’s velocity, you must also know the direction in which it is moving.
Velocity
11.2 Speed and Velocity
Vectors can be used to show changes in motion.
Velocity
11.2 Speed and Velocity
As the sailboat’s direction changes, its velocity also changes, even if its speed stays the same.
Velocity
11.2 Speed and Velocity
How do velocities add?
Combining Velocities
Two or more velocities add by vector addition.
11.2 Speed and Velocity
Sometimes the motion of an object involves more than one velocity.
If a boat is moving on a flowing river, the velocity of the river relative to the riverbank and the velocity of the boat relative to the river combine.
They yield the velocity of the boat relative to the riverbank.
Combining Velocities
11.2 Speed and Velocity
The velocity of the boat relative to the riverbank is a combination of the relative velocities of the boat and the river.
Combining Velocities
11.2 Speed and Velocity
The velocity of the boat relative to the riverbank is a combination of the relative velocities of the boat and the river.
Combining Velocities
11.2 Speed and Velocity
Assessment Questions
11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
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11.2 Speed and Velocity
�
Assessment Questions
11.2 Speed and Velocity
�ANS: F, kilometers per hour
Assessment Questions
11.2 Speed and Velocity