Average and Instantaneous Speed

How to Calculate

Average Speed

For example

Look at these two cars. They both are going to travel a certain distance.

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Different average speeds

Both cars are going to travel a total distance of 4 miles but they both may not reach the destination at the same time.

Multiple Choice

Why do both cars not reach the destination at the same time?

• They are driving at different speeds

• The cars are painted different colors

• The drivers are listening to different music

• Each car has a different number of cup holders

Different Speeds

One driver may drive slower or faster than the other driver.

Different speeds during journey

The drivers may not drive at the same speed throughout the entire 4 miles. Maybe one went 40 miles per hour for the first two miles then went 60 miles per hour for the last 2 miles.

Average Speed

A measurement of the average speed an object traveled takes into account all the variations in speed that may happen during a journey.

Average Speed

The higher an average speed number is, the faster that object completed its journey.

Calculating Average Speed

To calculate the average speed of an object you need to use the avearge speed formula.

Average Speed Formula

The S stands for Average speed

The D stands for Distance

The T stands for Time

Multiple Choice

What does the S stand for in the average speed formula?

• Average Speed

• Distance

• Time

Multiple Choice

What does the D stand for in the average speed formula?

• Average Speed

• Distance

• Time

Multiple Choice

What does the T stand for in the average speed formula?

• Average Speed

• Distance

• Time

Using the avearge speed formula

To calculate the average speed of an object you need to DIVIDE the distance an object traveled by the time. The distance number goes in the calulator first.

Multiple Choice

What number do you put into the calculator first when calculating average speed?

• Speed

• Distance

• Time

Multiple Choice

What do you have to do to the distance and time numbers?

• Divide them

• Multiply them

• Subtract them

• Add them

Lets practice calculating average speed

Use a calculator to help you! You need to score a 70 or above on this assignment to earn credit. You can take it as many times as you need to.

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Lets practice calculating time and distance

Use a calculator and the Speed Triangle to help you! You need to score a 70 or above on this assignment to earn credit. You can take it as many times as you need to.

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Calculating average speed using a graph

To calculate average speed you need to divide the distance by the time. You can get those numbers by looking at a graph.

Finding the distance

Look at the graph and notice that distance numbers are found on the left side of the graph. The highest distance number is 70.

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Finding the time

Look at the graph and notice that time numbers are found on the bottom of the graph. The highest time number is 7 seconds.

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Calculating average speed for the red line

Notice the red line went all the way up to 60 meters for distance. Put your finger at the top of the red line and move it over to the left and see that it lines up with 60 for distance.

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Calculating average speed for the red line

Notice the red line went out to 6 seconds. for time. Put your finger at the top of the red line and move it down and see that it lines up with 6 for time.

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Calculating average speed for the red line

So the distance is: 60

The time is: 6

What is the average speed of the red line?

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Reading a Distance vs. Time Graph

Read the information to the right about Distance vs. Time Graphs

Reading a Distance vs. Time Graph

To the right are some examples of the types of lines you will see on a Distance-Time graph. Notice that uniform motion means the same thing as constant speed and stationary body means the same thing as at rest.

Multiple Choice

Which of the graphs in the picture shows an object + accelerating (you can use your ISN)?

• D

• A

• B

• E

Multiple Choice

Which of the graphs in the picture shows an object at rest/stationary (you can use your ISN)?

• D

• A

• B

• E

Multiple Choice

Which of the graphs in the picture shows an object decelerating (you can use your ISN)?

• D

• A

• B

• E

Multiple Choice

Which of the graphs in the picture shows an object with the slowest constant speed (you can use your ISN)?

• C

• A

• B

• F

Multiple Choice

In the graph shown which two letters show where the monster accelerated (you can use your ISN)?

• C and H

• B and G

• D and C

• A and F

Multiple Choice

In the graph shown which two letters show where the monster was at rest/stationary (you can use your ISN)?

• C and H

• B and G

• D and C

• A and F

You should have scored at least an 80% on this assignment. If you did not go back and try it again. Use your ISN to help you.