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# Beginning the Chapter Project

What is a safe distance between cars traveling on the highway?  After you apply brakes to stop your car, how far will your car travel before coming to a full stop?  How do accident investigators determine whether cars involved in accidents were traveling at safe speeds?  There are many variables that affect how quickly a car can stop.  There variables include the car's speed, the driver's reaction time, the type of road, the weather conditions, and, of course, the effectiveness of the brakes.

As you work through the activities, you will use formulas to estimate safe speeds under various conditions.  You will make a graph to illustrate the relationship between speed and stopping distance.  Then, you will plan a skit with your classmates to illustrate what you have learned about safe highway driving.

# List of Materials

• Calculator
• Graph Paper
• Notebook Paper
• Computer
• Active Inspire
• Camera
• Car
• Scooter
• Helmet
• iMovie
• tackk.com

# Activity 1:Graphing

To reduce the likelihood of an accident when driving, you should consider how far your car will travel before safely coming to a stop for the speed at which you are traveling.  Assume you are traveling on a dry road and have an average reaction time.  The formula d=0.044s^2+1.1s gives you a safe stopping distance d in feet, where s is your speed in mi/h.  Make a table of values for speeds of 10, 20, 30, 40, 50, and 60 mi/h.  Then, graph the function.

***Refresh if pictures do not load.

As you can see from the table and graph above, for every 10 miles faster a person drives, the longer it would take to come to a complete stop, and the farther you travel as you slow down.

# Activity 2:Calculating

Suppose a car left a skid mark d feet long.  The formulas will estimate the speed s in miles per hour at which the car was traveling when the brakes were applied.

• Use the formulas to complete the table.  Round to the nearest mile per hour.

As you can see, if the roads are dry, and you want to keep a distance of 60 ft, then you are going to want to drive at a speed of 40 mph.  However, if you want to keep a distance of 120 ft on dry roads, then you are going to want to drive at a speed of 57 mph.

On the other hand, if the roads are wet, and you want to maintain a distance of 60 ft between you and the person in front of you, then you are going to want to drive at a speed of 28 mph.  But if you want to maintain a distance of 120 ft, then you are going to want to drive at a speed of 40 mph.

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• Why do you think the estimates of speed do not double when the skid marks double in length?  Based on these results, what conclusions can you make about safe distances between cars?

# Activity 3:Reasoning

Suppose you are driving on a dry road with 150 ft (about 10 car lengths) between your car and the car in front of you.  Use the formula from Activity 1 to find the maximum speed you should be traveling in order to leave a safe stopping distance.

Using the formula from Activity 1, you can determine that to leave a safe stopping distance between your car and the car in front of you, the maximum speed you should travel at is a speed of 47 mph.

# Activity 4: Communicating

Work with a group of your classmates to plan a skit that will demonstrate what you have learned about safe distances in driving.  Illustrate the relationships among reaction times, road conditions, speeds, and stopping distances.