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Section 5-8 The dashboard of your car gives you a lot of information about your car’s ability to go It gives no information about your car’s ability to stop How long do you think it takes just to switch from the gas pedal to the break pedal? The average, alert driver takes approximately ¾ of a second to 1 ½ seconds to switch from the gas pedal to the break pedal. This time is called the reaction time. How far does a car traveling 55 mph travel during this reaction time? How many feet are there in a mile? 5,280 ft = 1 mile How many feet does a car traveling 55 mph travel in 1 hour? (5,280 ft) x (55 mph) = 290,400 ft How many feet does a car traveling 55 mph travel in 1 minute? (290,400 ft) ÷ (60 min.) = 4,840 ft How many feet does a car traveling 55 mph travel in 1 second? (4,840 ft) ÷ (60 seconds) = 80.67 ft If your reaction time is 1 second, then in the time it takes you to realize you have to break your car will travel approximately 81 ft 1. Finding the distance traveled during reaction time Find the distance traveled in feet in one hour 1. Multiply mph by 5,280 2. Find the distance traveled in feet in 1 second 1. Divide step 1 by 3,600 3. Multiply step 2 by the reaction time A car is traveling at a speed of 65 mph. The driver of the car has a reaction time of 1.5 seconds. How far will the car travel during the driver’s reaction time? 1) Find the distance traveled in feet in 1 hour: → (65 mph) x (5,280 ft) = 343,200 ft A car is traveling at a speed of 65 mph. The driver of the car has a reaction time of 1.5 seconds. How far will the car travel during the driver’s reaction time? 2) Find the distance traveled in feet in 1 second: → (343,200) ÷ (3,600 ) = 95.33 ft 3) A car is traveling at a speed of 65 mph. The driver of the car has a reaction time of 1.5 seconds. How far will the car travel during the driver’s reaction time? Find the distance traveled during the reaction time: → (95.33) x (1.5 ) = 143 ft A car is driving on a rural road at a speed of 40 mph. The driver has a reaction time of 0.75 seconds. Find the reaction distance. 1) (40 mph) x (5,280) = 211,200 ft 2) (211,200 ft) ÷ (3,600) = 58.66 ft 3) (58.66) x (0.75) = 44 ft Page 272, Numbers: 1-3, 7 & 8 Section 5-7 1) Previously, we covered two main topics: Reaction time 1) The time it takes you to realize you need to brake 2) Reaction distance 1) The distance traveled during your reaction time What major factor do neither the reaction time or reaction distance account for? Note, both of those statistics just cover how long and how far the car travels before you realize you have to brake They do not take into account how long it takes your car to break The distance a car travels while braking to a complete stop is called the braking distance What is the difference between braking distance and reaction distance? Why can braking distance vary depending on time of year, location, etc.? The general formula we will use for braking 2 distance is: s B.D. 20 where “s” represents the speed of the car Find the braking distance of a car traveling 48 mph. 2 s s 48 B.D. 20 2,304 (48)2 B.D. 115.2 20 20 It will take this car approximately 115.2 ft to come to a complete stop. Find the braking distance of a car traveling 65 mph. 2 s s 65 B.D. 20 4,225 (65)2 B.D. 211.25 20 20 It will take this car approximately 211.25 ft to come to a complete stop. Section 5-7 So far, we have covered two major concepts: 1) Reaction Time/Distance 1) The time or distance you travel before you realize you need to brake 2) Average between 0.75 and 1.5 seconds 2) Braking Distance 1) The distance your car travels from the time you start braking and when your car comes to a complete stop Today, we will cover the final piece to these concepts Total Stopping Distance The distance a car travels from the moment a driver realizes the need to stop to the time that the car comes to a complete stop Total Stopping Distance The formula for this is just the sum of the reaction distance and braking distance s2 =s 20 Where s is equal to the speed of the car You are driving 65 mph on the highway. What is your total stopping distance? 2 s Stopping Distance = s 20 2 65 65 + = 65 + 211.25 = 276.25 20 You have a total stopping distance of 276.25 ft You are driving at 55 mph on a highway. You see an accident directly ahead of you about 200 feet away. Will you be able to stop in time? s2 Stopping Distance = s + 20 552 = 55 + 151.25 = 206.25 = 55 + 20 You will not be able to stop in time