NATURAL LAWS AND CAR CONTROLCHAPTER 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 parkedcar parked.

Inertia keeps this movingcar and everything init moving until acted upon by another force.

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

straight line.

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…

you seem to be pushed back into your seat.

Momentum… 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… 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 stopping50 miles per hour distance 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

4X

Gravity…

Is the force that pulls all thinks to Earth.

When you drive uphill, thepull of gravity will cause you to losespeed. When you drive downhill, The pull of gravity will causeyou to go faster.

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

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 Only four small areas underneath each

tire holds the vehicle on the road. This is called its footprint andare all you have for traction on thesurface of the road. Tread provides the traction forStarting, stopping, and gripping the road.

Inflation and Traction

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

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 Used to accelerate, brake and steer Even under ideal conditions, your tires

provide a limited amount of traction.

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 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

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 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

Forces in Curves Factors affecting your ability to control

your vehicle in a curve1. 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 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

PT

The length of time it takes you to identify a

hazard, predict a conflict, and decide to

break.

¾ second

PD

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

Reaction Time and Distance

RT The time from

identifying a hazard and applying the brake.

¾ second

RD The distance your

vehicle travels while you react.

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

Force of Impact The force with which a moving object

hits another object. Three Factors determine the force of

impact

Speed 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

Weight 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

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.

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

ortheir restraint devices.

Restraint Devices

Active Must be engaged

by you Safety Belt

Passive Automatically

works Airbags

WEARING A SAFETY BELT IS YOUR FIRST DEFENSE IN AN EMERGENCY!!!

WHY????

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…

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 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

Frontal Only deploy

when there is a crash in the front of the vehicle.

Side Designed to

protect your head and chest.

Protect from injury and from ejection during a rollover.

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 All states have laws that require proper

restraints for infants and children.

Infants 20 Pounds or Less Rear-facing car seat

20 Pounds and Over Forward-facing car seat

13 and Younger

Back seat riders

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