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4. Physics and Natural Laws

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19. Formulas for Driving Success

How Fast Am I Going?

Take your Speed, add 1/2 your Speed. The result is your speed in feet per second.


S + 1/2S = S (feet / second)

How Long Will it Take to Stop?

Take your speed, multiply it by 1/10 of your speed and divide the result by two. The result is your stopping distance, after the brakes are applied, in feet.


(S x 1/10S)/2 = SD (feet)

How Long Will it REALLY Take?

Since it takes about one second to recognize a danger and then react to it, add the distance you travel in one second to the stopping distance to find the total distance, in feet, it will take you to stop.


(S + 1/2S) + (S x 1/10 S /2) = Total Stopping Distance (feet)

What is Kinetic Energy, and what effect does it have on me?

Kinetic Energy, or momentum affects all aspects of driving. To stop a moving vehicle, you must dissipate (get rid of) the kinetic energy through the friction of the brakes or by hitting another object (called the Force of Impact). To steer the car, you must overcome the kinetic energy of the vehicle (it wants to keep going in a straight line) in order to change direction.


KE = 1/2M x V

Any increase in the mass (weight) of the vehicle will proportionately increase the KE. Doubling the mass will double the KE.


Any increase in the velocity (speed) of the vehicle will increase the KE by the square of the change in speed. Doubling the velocity will quadruple the KE.


Most importantly, you can control the KE! By the simple act of braking and reducing your speed in half, the KE is now only one-fourth (1/4) from what it was at your original speed! The less KE there is, the less damage that occurs to both you and your vehicle in a crash.


What is the Coefficient of Friction?

This is the amount of traction provided by the "footprint" of the four tires in contact with the road. Four brand new tires, on a perfectly smooth surface, gives a CF of 1.0 ; on smooth, dry asphalt the CF is 0.9 ; on wet pavement or melted ice, the CF is only 0.35 ; frozen asphalt gives a CF of 0.20 ; and ice has a CF of only 0.05 !




Lesson Summary


  

Lesson 4 Quiz


You will now answer 5 questions to test what you learned during this lesson. You must answer all questions correctly to receive completion credit for this lesson. You may answer the questions as many times as necessary to get them right.

You should review the lesson material if you don't do well on the quiz.

  1. According to the formula for stopping distance, how many feet will it take you to stop, from 60 mph?


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  2. Gravity:


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  3. Centrifugal force:


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  4. The primary factor in decreasing the Kinetic Energy of an object is to:


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  5. The best way to maximize the traction of your tires is to:


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