Chapter 5 - Elmwood Park Community Unit School District #401

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14 Νοε 2013 (πριν από 4 χρόνια και 4 μήνες)

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Drive Right

Chapter 5

Natural Laws and Car Control

Unit 3

Theory Notes from


Driver Education


5.1 Gravity and Energy of Motion

Gravity and energy of motion are both
natural laws that will effect the way your
vehicle performs.

When you operate a small vehicle, like a
bicycle, it is easy to control it because of
the low speed and weight.

A car or SUV can weigh as much as two
tons (4,000 lbs)!!

Natural Laws can create forces that work
against you in emergency situations.

5.1 Gravity and Energy of Motion

Gravity is the force that pulls all things
to the earth.

Gravity pulls your car towards the earth
when you are driving.

5.1 Gravity and Energy of Motion

You can feel the pull of gravity as you
drive up and down hills.

When you drive uphill, you will lose
speed unless you use extra power (gas

If you want to maintain the same speed,
you must increase the power to
overcome the force of gravity.

5.1 Gravity and Energy of Motion

Gravity will increase your speed on a
downhill road unless you control it.

It will take you longer to stop, so you will
need to brake earlier and downshift.

Downshifting allows the engine

not the
brakes slow the vehicle down.

5.1 Gravity and Energy of Motion

How does uphill or downhill situations
affect your intended path of travel?? 3


your braking distance will
actually decrease.


your braking distance will be

The steeper the incline, the longer your
or shorter your stopping distance.

5.1 Gravity and Energy of Motion

What is the definition of Center of Gravity

The point around which an object’s
weight is evenly distributed is called it
center of gravity.

Example: Circus high wire performers
use poles to maintain their center of

5.1 Gravity and Energy of Motion

More examples of Center of Gravity

Engineers try to make a vehicle’s center
of gravity low so it can perform better.

The higher the center of gravity

more unstable it becomes on steep hills
and sharp turns.

5.1 Gravity and Energy of Motion

Energy of Motion

When objects move, it acquires energy.
This force is called Energy of Motion or
Kinetic Energy.

The faster your vehicle moves, the more
energy of motion it has.

Energy of motion is also affected by the
weight of the moving object.

5.1 Gravity and Energy of Motion

Energy of Motion

When the weight and speed of a vehicle
increases, the stopping distance

If the weight doubles

the stopping
distance doubles.

The stopping distance will change in
proportion to the square of its change in
speed. When the vehicles speed

the stopping distance is about
four times as long.

5.1 Gravity and Energy of Motion

Energy of Motion

Speed Kills!!

We all understand the dangers of speeding.

You will develop an ability to adjust to
traffic situations ahead of time. You will
see how important it is to slow before an
emergency situation develops.

Every time you cut your speed in half, you
cut your energy of motion by four times!

5.1 Gravity and Energy of Motion

Energy of Motion

As you gain experience with driving, you
will feel the laws of gravity and energy of
motion affecting your car.

Remember these laws when you need to
judge how long it will take you to stop your

5.2 Friction and Traction

Your four tires are the most important
factor in controlling your car.

In reality, your car makes tracks similar to
an animal walking in the mud or snow.

Each footprint is approximately twice the
size of your hand.

5.2 Friction and Traction


Is the force that keeps each tire from
sliding on the road.

You can feel this same force by rubbing
your hands together.

5.2 Friction and Traction


The friction created by the tire on the road
is called traction.

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

5.2 Friction and Traction


Tires make a difference in the way your
vehicle performs.

Proper tire pressure can mean the
difference in avoiding a crash and hitting

5.2 Friction and Traction


The grooved surface of a tire that grips the
road is called the tread.

When the road is wet the tread allows water
to flow through the grooves.

This action allows the tire tread to cut
through the water and grip the road.

5.2 Friction and Traction


Warn or bald tires are dangerous.

A bald tire will not grip a wet or icy road.

Since it has no tread to push the flow of
water away from the ground.

It is also more vulnerable to a puncture or

5.2 Friction and Traction


Tires are designed to work best when they
are properly inflated.

Check the owner’s manual for best
pressure to use.

When your tire pressure is right, you will
get the best control from your tires.

5.2 Friction and Traction


Under Inflation: Only the outside edges of
the tire provide traction.

Split Traction: You are dividing your
traction between stopping, starting and

You have reduced traction based on the

5.2 Friction and Traction

Reduced Traction

Ideal levels of traction can be maintained

Vehicle is in good mechanical condition.

The road must be smooth, paved, level,
and clean.

5.2 Friction and Traction

Vehicle Condition

The older your vehicle

the more important
it is to properly maintain it.

Good shocks are necessary to prevent your
vehicle from bouncing.

Worn tires limit your control.

5.2 Friction and Traction

Road Condition

It is easy to drive on straight, dry, flat roads.

Obviously snow or rain will effect that same roadway.

Reduction in speed is the safest way to handle poor
roadway conditions.

Checking Traction: When road conditions are bad,
slow down your vehicle. You can use these steps to
check how much traction you have:

Check your rear zone to make sure no traffic is

Brake gently to see how your vehicle will respond.

If your vehicle does not slow or if your antilock
brakes start to work, reduce speed even further.

5.2 Friction and Traction


Energy of motion and traction will work on your vehicle as
you drive around a curve.

The energy of motion in your vehicle will try to make it go
straight in a curve.

The higher your vehicle’s speed, the more it will tend to go

Vehicle Control in Curves:


slow down to reduce your chance of skidding.

Sharpness in Curves

the sharper a curve, the more
traction your vehicle needs to grip the road.

Banked Curves

a curve that is higher on the outside
than it is on the inside is called a banked curve. It
helps in the prevention of your car moving to the
outside of the curve.


your vehicle’s load affects your control in a

5.3 Stopping Distance


When you are driving and have to stop,
three things must happen:

You must perceive the hazard in your
path of travel


Brake your car to a stop

The distance your car travels while you
make a stop is called your
Stopping Distance.

5.3 Stopping Distance

Total Stopping Distance

Total Stopping Distance is the distance
your car travels while you are attempting to
stop it.

The picture on Page 98 shows the distance
it take once you see a hazard to the point
where you stop your vehicle.

5.3 Stopping Distance

Perception Time and Distance

The length of time you take to identify,
predict, and decide to slow for a hazard is
called your perception time.

Perception time will vary greatly depending
on visibility, the hazard, and your abilities
at the time.

The distance your vehicle travels during
this time is your perception distance.

Perception Distance is not easy to estimate.

It will vary as driving situations change and
become more complex.

5.3 Stopping Distance

Reaction Time and Distance

Once you recognize a hazard, the length of
time you take to execute your action is your
reaction time.

The average driver’s reaction time is

of a second.

The distance your vehicle travels is called
your reaction distance.

5.3 Stopping Distance

Braking Distance

The distance your vehicle travels from the
time you apply the brake until you stop is
called braking distance.

A vehicle’s energy of motion

and your
braking distance

are proportional to the
square of the increase in speed.

If you accelerate from 20 to 40 mph, your
braking distance will be 4 times longer.

5.3 Stopping Distance

Estimating Stopping Distance

The chart on page 99 shows
your reaction distance and
braking distance from
different speeds.

Use the four second rule,
which enables you to project
your approximate stopping
distance under ideal
conditions at any speed.

5.3 Stopping Distance

Estimating Stopping Distance

Pick a fixed checkpoint
ahead where you think you
could stop.

Count off four seconds: one
one, one
two, etc.

Check your vehicles position.
If you have just reached your
fixed checkpoint, you can
assume the distance you
estimated in step 1 was

5.3 Stopping Distance

Factors that Affect Braking Distance


higher speed

longer distance.

Vehicle Condition

worn tires or shocks

distance to stop.

Roadway Surface

Rain, snow, ice, dirt, etc.
reduce traction and increase distance.

Driver Ability

If you are distracted or impaired,
your will take longer to stop.

Antilock Braking System (ABS)

You can better
control your stopping distance in curves.


Your braking distance increase downhill.


Heavy loads increase your braking

5.4 Controlling Force of Impact

Accidents happen in a blink of an eye. It is
imperative that you do everything in your ability
to protect yourself and your passengers.

Forces of Impact:

In violent collisions, occupants need protection at all
times. If they are not protected, they will be
thrown against the vehicle’s interior in a second
collision or ejected from the vehicle.

The force with which a moving object hits another
object is called Force of Impact.

Three factors determine how hard something will hit
another object:



Distance between impact and stopping

5.4 Controlling Force of Impact

Force of Impact


The most important factor in
determining how hard a vehicle will hit
another object.

The force of impact is in proportion to
the square of the increase or decrease in
the vehicle’s speed.

Any reduction in speed will greatly
reduce the damage inflicted.

Always try to reduce speed in an

5.4 Controlling Force of Impact

Force of Impact


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.

5.4 Controlling Force of Impact

Force of Impact

Distance Between Impact and Stopping:

The distance a vehicle covers between the
instant it hits an object and the moment it
comes to a stop can vary greatly.

Image hitting barrels filled with sand sitting in
front of a light post rather than hitting the post

The barrels will slow you as you hit them
rather than stopping you like the post would.

This is why traffic engineers put cushioning
materials in front of solid roadside objects.

5.4 Controlling Force of Impact

How to Wear Safety Belts

Using safety belts is the #1 defense to
reduce possible injury.

They hold you in place and prevent you
from being thrown from the vehicle.

Follow these steps with your seatbelt

Adjust your seat to an upright position.

Make sure your seatbelt is not twisted.

Snap the buckle into place and tighten the
lap portion across your hips.

Adjust the shoulder strap across your
chest. Make sure it is snug.

5.4 Controlling Force of Impact

Air Bags

Air bags will automatically inflate to
protect you during a collision.

It is a balloon type device.

It takes approximately 25 thousandths of
a second.

They will deploy in speeds over 200

5.4 Controlling Force of Impact

Air Bags

Air bags are designed to work with seat belts.

To prevent air bag injuries keep your hands at
3 or 8

Sit away from an air bag after your are belted.
Your chest should be 10” away from the
steering wheel.

If you have a tilt steering wheel, tilt it so your
air bag will deploy toward your chest.

Children in a child seat and young people
under age 12 must sit in the back seats. They
can be injured when an air bag deploys.

5.4 Controlling Force of Impact

Air Bag Improvements

Engineers are now developing numerous
features to make air bags even more effective.

Advanced Air Bags: because of previous
injuries, some air bags can measure your
seat position and weight of passengers.

The air bag can deploy in two stages with
appropriate speed and intensity.

Some owners have air bag switches
installed to give vehicle owners a choice
about using an air bag.

Check with your insurance policy to see if
it is still valid and make sure your seat
belts don’t stretch.

5.4 Controlling Force of Impact

Other Protection Devices

Engineers have designed additional devices
in new vehicles to protect you:

Automatic Seat Belts

Front and Rear Crash Areas

Absorbing Bumpers

Side Door Beams

Reinforced Windshields

Absorbing Steering Wheel

Padded Dash

Child Seats

Head Restraints