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
it 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
4X
50 miles per hour



60 feet stopping
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
Gravity…
 Is
the force that pulls all thinks to Earth.
 When
you drive uphill, the
pull of gravity will cause you to lose
speed.
 When you drive downhill,
The pull of gravity will cause
you 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 and
are all you have for traction on the
surface of the road.
 Tread provides the traction for
Starting, 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 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
 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.

PD




¾ second

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
RD
 The
 The
time from
identifying a hazard
and applying the
brake.
 ¾ second
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
or
their restraint devices.
Restraint Devices
Active
 Must
be engaged by
you
 Safety Belt
Passive
 Automatically
 Airbags
works
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
Side
 Designed
Frontal
 Only
deploy when
there is a crash in
the front of the
vehicle.
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