Natural laws and car control chapter 9
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NATURAL LAWS AND CAR CONTROL CHAPTER 9. Laws of Motion…. How do they affect your ability to drive??. Inertia. Objects at rest tend to stay at rest and objects that are moving tend to keep moving. Inertia keeps this parked car parked. Inertia keeps this moving car and everything in

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Natural laws and car control chapter 9


Natural laws and car control chapter 9

Laws of Motion….

How do they affect your ability to drive??



  • Objects at rest tend to stay at rest and objects that are moving tend to keep moving.

  • Inertia keeps this parked

    car parked.

  • Inertia keeps this moving

    car and everything in

    it moving until acted upon

    by another force.

D riving around a curve inertia causes your body to continue in a straight line

driving around a curve. Inertia causes your body to continue in a straight line.

As the car decelerates

As the car decelerates…

  • The force of friction on the brakes causes the car to slow down.

  • You feel this when you are pressed against your safety belt.

As the car accelerates rapidly

As the car accelerates rapidly…

  • you seem to be pushed back into your seat.



  • Momentum is inertia in motion or the tendency of an object to stay in motion.

  • Momentum depends upon of speed and weight of an object.

  • A heavy vehicle has more momentum than a light vehicle.

  • A fast car has more momentum than a slow car.

Energy of motion

Energy of motion…

  • is the kinetic energy of a moving object.

  • It is the work needed to accelerate or decelerate and object

    15 feet stopping distance

    25 miles per hour

    60 feet stopping

    50 miles per hourdistance

  • A vehicle’s energy of motion is proportional to the square of its speed.

  • Double speed=4x as much energy

  • Double weight=2X stopping distance




  • Is the force that pulls all thinks to Earth.

  • When you drive uphill, the

    pull of gravity will cause you to lose


  • When you drive downhill,

    The pull of gravity will cause

    you to go faster.

Tires and traction

Tires and Traction

Even though you control your vehicle by using the steering wheel, accelerator, and brake pedal, your tires are a key part to your control system.

  • Friction is the force that acts between materials as they move past each other.

  • Keeps a tire form sliding on the road

Natural laws and car control chapter 9

  • When tires run over the surface of the road they create a form of friction called traction.

  • Traction makes it possible for your vehicle to grip the road so that you can control speed and direction.

  • Acceleration causes the tires on the drive wheels rotate pushing you forward.

  • During deceleration, as the tires on the wheel slow, traction between the tires and the road will slow your vehicle.

Tire tread and traction

Tire Tread and Traction

  • Only four small areas underneath each tire holds the vehicle on the road.

  • This is called its footprint and

    are all you have for traction on the

    surface of the road.

  • Tread provides the traction for

    Starting, stopping, and gripping the


Inflation and traction

Inflation and Traction

  • Properly inflated tires can mean the difference between keeping or losing control.

Inflation and traction continued

Inflation and Traction continued…

  • Underinflation will shorten the life of the tire and will accept less stress before losing its grip on the pavement.

  • Overinflation of a tire will cause the tire to have a smaller footprint so the tire will have less traction.

  • Temperature can change the pressure in tires.

  • Colder weather causes pressure to drop.

  • Hot weather will increase pressure.

Using traction

Using Traction

  • Used to accelerate, brake and steer

  • Even under ideal conditions, your tires provide a limited amount of traction.

Traction continued

Traction continued…

  • Braking hard and steering may consume most of your traction in emergency situations.

  • Skidding is a result and you may lose control.

  • To regain control change traction forces by turning the wheel sharply in to curve.

Ensuring good traction

Ensuring Good Traction

  • Vehicle Condition

    -Check tire pressure and tread often

    -Replace worn shock absorbers

    • Road Conditions

      -Good traction on dry, flat road

      -reduced traction on gravel, snow, ice, leaves, sand and oil (REDUCE SPEED)

    • Your actions affect your ability to maintain traction so try to maximize your traction by steering, accelerating, and braking gently and smoothly

Vehicle balance and control in curves

Vehicle Balance and Control In Curves

  • Your ability to control your vehicle is affected by its balance.

  • Vehicle balance is the distribution of a vehicle’s weight on its tires ads they contact the ground.

  • Only perfect when car is not moving

Center of gravity

Center of Gravity

  • Point around which an objects weight is evenly distributed

  • The lower the center of gravity, the more stable the vehicle

  • Taller, narrow vehicles with a higher center of gravity tend to be less stable

Balance and steering

Balance and Steering

Forces in curves

Forces in Curves

  • Factors affecting your ability to control your vehicle in a curve

    1. Sharpness of curve- the sharper the curve, the more traction your tires need to grip the road in order to overcome inertia.

    2. Speed and weight of vehicle-The momentum of your vehicle increases speed. The faster you go, the more traction you need to overcome momentum. If you go to fast, your vehicle might not be able to make the turn.

    3. Shape of roadway

Stopping distance

Stopping Distance

  • When you have to stop quickly, you must perceive the hazard in your path of travel, react, and brake to a safe stop.

  • Total Stopping Distance- distance your car travels from the time you first perceive a hazard until you reach a full stop.

  • Insert figure 8 here

Perception time and distance

Perception Time and Distance



The distance your vehicle travels during your perception time

Varies depending upon visibility, alertness, and your line of sight.

Can improve perception time by using IPDE

12-15 seconds ahead

  • The length of time it takes you to identify a hazard, predict a conflict, and decide to break.

  • ¾ second

Reaction time and distance

Reaction Time and Distance



The distance your vehicle travels while you react.

  • The time from identifying a hazard and applying the brake.

  • ¾ second

Braking distance

Braking Distance

  • The distance your vehicle travels from the time you apply the brake until you stop.

  • It is proportional to the square of your speed

  • example- 40 mph…

  • Is affected by driver ability, speed, vehicle condition, roadway surface, hills, and the weight of vehicles load.

Controlling the force of impact

Controlling the Force of Impact

Force of impact

Force of Impact

  • The force with which a moving object hits another object.

  • Three Factors determine the force of impact



  • A vehicle’s momentum is proportional to its speed and weight.

  • Higher the speed the more the damage

  • Always try to reduce speed in an emergency



  • The heavier a vehicle, the more damage it will cause in a collision.

  • A vehicle weighing twice as much as another vehicle will hit a solid object twice as hard.

Time between impact and stopping

Time Between Impact and Stopping

  • How quickly a vehicle stops affects the force of impact.

  • If a truck hits a stone wall, the force of impact is great because the collision occurs in a brief moment.

  • If the same truck hits a patch of bushes, the truck will come to a stop more gradually, and there will be less damage.

Natural laws and car control chapter 9

  • When a vehicle hit’s an object, inertia causes the driver and passengers to continue forward until they hit either….

    the inside of the vehicle


    their restraint devices.

Restraint devices

Restraint Devices



Automatically works


  • Must be engaged by you

  • Safety Belt

Wearing a safety belt is your first defense in an emergency



  • Safety belts hold you in place and prevent you from being thrown from the vehicle.

  • Distributes the forces of rapid deceleration over larger and stronger parts of the body(pelvis, chest, and shoulders)

Safety belts continued

Safety Belts continued…

  • Consist of lap belt and shoulder belt

  • During a collision, the reels of the belt will suddenly tighten up and hold you in place.

To ensure maximum protection from y our safety belt

To Ensure Maximum Protection From Your Safety Belt…

  • Adjust you seat back to an upright position.

  • Click the belt’s latch in the buckle.

  • Lap belts should be low and snug across hips.

  • Adjust shoulder belt snuggly across chest and collarbone.

  • NEVER wear it under your arm or behind your back!!

Air bags

Air Bags



Designed to protect your head and chest.

Protect from injury and from ejection during a rollover.

  • Only deploy when there is a crash in the front of the vehicle.

Using airbags effectively

Using Airbags Effectively

  • Designed to work with safety belts. So make sure you always buckle up.

  • Keep hands at 9 and 3 or 8 and 4.

  • Seat needs to be at least 10 inches from the hub of the steering wheel.

  • Front passenger seats need to be back as far as possible. The passenger side airbag is 2-3 larger than the driver’s.

Child passenger safety

Child Passenger Safety

  • All states have laws that require proper restraints for infants and children.

Infants 20 pounds or less

Infants 20 Pounds or Less

  • Rear-facing car seat

20 pounds and over

20 Pounds and Over

  • Forward-facing car seat

13 and younger

13 and Younger

  • Back seat riders

Other protective devices

Other Protective Devices

  • Crush Zones- front and rear ends absorb force

  • Energy Absorbing Bumpers- absorbs low levels of impact without damage

  • Side-Impact Panels-absorbs crash energy and reduces the risk of penetrating objects

  • Penetration- Resistant Windshields- made with plastic between 2 layers of glass

  • Head Restraints- Padded and protects against whiplash

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