Driving Lesson 3

You can reduce the force on you and your car during an unavoidable crash if you redirect your path toward objects that will cause your car to stop over a greater distance, such as:

-Bushes rather than trees -Snow -Soft dirt -Sand barrels placed in front of freeway abutments

Natural forces that act on your vehicle include:

-Gravity -Inertia -Momentum -Kinetic energy -Potential energy -Friction -Centrifugal force Understanding these forces will help you control your vehicle during everyday driving and emergencies. By misjudging natural forces, you might lose control while making a turn or lose traction on wet pavement and be unable to stop.

Avoid:

-Riding your brakes -Driving with your clutch partially engaged (depressed) -Using lower gears to slow your vehicle on downhill grades (downshift) Friction can be reduced through lubrication. Improper lubrication of your engine and transmission will cause excessive friction and eventually mechanical failure.

Modern vehicles have features that reduce the forces on your body during a crash by absorbing energy and increasing the distance over which the impact occurs. These include:

Airbags, which absorb the momentum of your body over a slightly greater distance than the steering wheel or windshield Crush zones, or areas of the vehicle designed to absorb impact by collapsing without harming the passenger area of the vehicle I-beam construction in the frame and doors to give the vehicle more rigidity Energy-absorbing bumpers that reduce the effect of kinetic energy during a front or rear-end collision Padded dashboards Safety-glass windows and windshields designed to crumble into small, dull-edged pieces to reduce lacerations Seat belts are the best protection against ejection from the car and other life-threatening injuries

Effect Of Kinetic Energy On Driving

As you increase your driving speed, both your body and your vehicle acquire kinetic energy that eventually must be: -Absorbed by your brakes, engine-compression forces, or other friction in a controlled stop -Absorbed by your body, your vehicle's body, and the objects you hit if you're involved in a crash The kinetic energy of your body when it is in motion, loose objects in the car, and the car itself all increase with weight and the square of your speed so that: -If you increase your speed from 10 mph to 20 mph, you're dealing with 4 times the amount of kinetic energy -If you increase your speed from 10 mph to 50 mph, you're dealing with 25 times the amount of kinetic energy

Stopping

Friction is increased by the weight of your vehicle. A fully loaded truck has more stopping power than an empty one because it is heavier. The additional weight helps to stop the vehicle by producing more friction between the tires and the road surface. The kinetic energy of a moving vehicle is converted into heat during braking due to the friction of the brakes against the wheels and the friction of the tires against the road.

Friction

Increased by the weight of your vehicle Decreased if tires are overinflated or worn smooth Increased if tires are underinflated Affected by materials used to construct the road Affected by road-surface conditions, including factors due to weather Friction occurs between your tires and the road, in your brakes when applied, and in many parts of your engine and transmission

Chapter 3 Review

Gravity affects the speed of travel when you're heading uphill and downhill. If your vehicle is hit from behind while stopped, your head tends to stay in place due to inertia, while the rest of your body is pushed forward by the seat. This causes whiplash. Properly adjusting your headrest reduces injuries due to whiplash. Wearing a seat belt while driving will stop the forward momentum of your body if you have a collision. It will prevent you from hitting the windshield, steering wheel, and other parts of the interior of your vehicle. Worn or over-inflated tires will decrease the friction between your tires and the road surface, reducing the traction needed to start smoothly, stop quickly, and pull out of a turn or curve without losing control. Road-surface changes due to ice, rain, snow, oil and diesel fuel buildup, or sand and dirt will reduce the friction and traction of the tires and can cause you to lose control of your vehicle. Modern vehicles have features that reduce the forces on your body during a crash by absorbing energy and increasing the distance over which the impact occurs. However, if the force of impact is excessive enough, these safety features may still not be enough to prevent serious injury or death. Always be a safe, cautious, and prepared driver Always wear your seat belt!

Vehicle Components

The friction that the clutch creates when released can: -Cause a loss of traction if released improperly (peeling out) -Slow your vehicle by engaging a lower gear -Allow the vehicle to move regularly Friction wears out your brakes and clutch, and using your brakes and clutch improperly causes excessive wear.

Traction

Traction is the result of friction between the road and your tires caused by the weight of the car (the pull of gravity). Traction is a vital component of driving because you need traction to steer.

Parking on an Incline

When you leave a vehicle parked on an incline, gravity pulls your vehicle downhill. To keep your vehicle from rolling away, leave it in a low gear or in "Park" if it has an automatic transmission. Always engage your parking brake. Review: Review Lesson 1 quizlet for the proper procedures for parking correctly on a hill.

Centrifugal Force And Its Effect On Turns

When you turn, your car is subject to the centrifugal force that pulls it away from the direction you want to turn and into a straight line. Traction is necessary to keep you from losing control of your car during a turn. Banked roadways improve your traction during turns and help in overcoming the centrifugal force that pulls your car away from the direction in which you want to turn. To keep a vehicle in a turn without allowing centrifugal force to pull the car out, you should: -Decelerate before the curve -Brake gently and gradually while turning -Downshift if your car has a manual transmission

Driving Uphill and Downhill

When you're driving uphill, the force of gravity is working against you to slow you down, and you may need to accelerate or shift to a lower gear to maintain your speed. When you drive downhill, the reverse is true. Gravity will cause you to go faster and increase your stopping distance. You may need to shift to a lower gear or smoothly apply your brakes to slow to a safe speed and control your vehicle.

Effect Of Inertia On Driving

While driving, inertia keeps your vehicle moving unless the vehicle is stopped by something, such as your brakes, the road surface, a fixed object (such as a tree), or another vehicle. Inertia also causes your body and loose objects in the car to keep moving forward if your vehicle comes to a sudden stop. When you're stopped and hit from behind, your head tends to stay in place due to inertia while the rest of your body is pushed forward by the seat. This causes whiplash. Properly adjusting your headrest can reduce injury due to whiplash.

Effect Of Roads And Tires

Worn or over-inflated tires will decrease the friction between your tires and the road surface, reducing the traction needed to: -Start smoothly -Stop quickly -Pull out of a turn or curve without losing control Road surface changes due to ice, rain, snow, oil and diesel fuel buildup, or sand and dirt. These elements will reduce the friction and traction of your tires and could result in you losing control of your vehicle.