This lesson will deal with how the laws of nature
affect your ability to control your vehicle.
The laws we’ll consider are:
- Gravity (its effect on time and space management)
- Kinetic and potential energy
- Friction and centrifugal force
- Factors that affect stopping ability
- Forces of Impact
These forces affect how your vehicle handles so you
may react appropriately in emergency situations.
The Law of Gravity:
time and space management
If you break the laws of nature or misjudge
them while driving you may end up losing
control and get into a collision.
Let’s first think about gravity.
Gravity is the force
that pulls all objects
toward the center of
the earth. It affects
your speed of travel
when going uphill
and down hill.
When you are driving uphill, the force of
gravity is working against you.
Your traction could be
reduced depending upon
road conditions.
When you are driving downhill, the force of gravity
will cause you to go faster and could also reduce
your traction and increase your stopping distance.
To control your vehicle
you may need to brake
or change to a lower
gear to slow to
a safe speed.
Even though this message is especially for trucks,
other vehicle users must be ready to reduce speed to
compensate for a possible loss of traction due to gravity
and wet pavement.
With poor traction, space management
is also very important.
What should you do in this situation?
80
km/h
REACTION DISTANCE
BRAKING DISTANCE
STOPPING DISTANCE
55 to 65 meters
80
km/h
REACTION DISTANCE
BRAKING DISTANCE
55 to 65 meters
100
km/h
REACTION DISTANCE
STOPPING DISTANCE
BRAKING DISTANCE
STOPPING DISTANCE
75 to 92 meters
The greater the speed, the greater the distance
needed to brake the vehicle to a stop.
Obviously following too closely can result in a rear end
collision…drop back to increase following distance
Kinetic Energy
Kinetic energy is the
energy a body possesses
because it is in motion.
As you increase your driving speed, both your body
and your vehicle acquire kinetic energy (motion)
which eventually must be:
a) absorbed by your brakes, engine compression
forces, or other friction in a controlled stop.
b) absorbed by your body, and the objects you hit if
you are involved in a crash.
Kinetic Energy
Kinetic energy is the
energy a body possesses
because it is in motion.
The kinetic energy of your body while it is in motion,
of 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 16 km/ph to 32 km/ph
you are dealing with four times the amount of kinetic
energy, and if you increase your speed from 16 km/ph to
80 km/ph you have to deal with 25 times the amount of
kinetic energy. With increased speed, increase following
distance.
Kinetic Energy
Kinetic energy is the
energy a body possesses
because it is in motion.
Gravity decreases your kinetic energy when you are
driving uphill, making it easier to stop. When going
downhill, it increases, making it more difficult to stop.
Braking to a stop converts kinetic energy into heat
energy in your brakes by the friction that is generated.
But, if you and your vehicle are involved in a collision,
the kinetic energy is still converted into heat energy,
but not through your brakes…you and your car must
absorb that energy! (ouch)…but…
Kinetic Energy
Wearing a seatbelt 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.
Check to see
that it is
properly adjusted
If you are 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.
Using your headrest minimizes injuries.
Momentum
Momentum is the force
of a moving object. The
momentum of an object
is proportional to its
weight and speed.
For example, a baseball traveling at 16 km/h
has more momentum (force) than a ping
pong ball traveling at the same speed.
When driving, you and you vehicle acquire a
momentum which is proportional to the weight of
your vehicle and its speed. Increasing your speed
from 16 to 32 km/h, doubles your car’s momentum
From 16 to 80 km/h, you increase it 5 times.
Momentum
Momentum is the force
of a moving object. The
momentum of an object
is proportional to its
weight and speed.
You may also be injured because of the inertia and
momentum of loose objects that become airborne
during a sudden stop.
When in a crash, the momentum and kinetic energy
of your vehicle must be absorbed, which results in
heat, the deformation of your vehicle, and possibly
injury to your body.
Friction
Friction is the force
caused by the contact of
one surface on another.
It results in the resistance
of an object moving over
a surface.
For example, it is easier to move your hand over
writing paper than over rough sandpaper because
there is less friction.
Friction is (a) increased by the weight of your vehicle
(b) decreased if you tires are over-inflated or worn
smooth, (c) increased if your tires are under-inflated
(d) affected by the materials to construct the road,
and (e) affected by the condition of the surface of the
road.
Friction
Friction occurs (a) between
your tires and the road,
(b) in your brakes when
applied, and (c) in many
parts of your engine and
transmission.
Because 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
weight helps stop the vehicle
by producing more friction
between the tires and the road.
Friction
The kinetic energy of your
moving vehicle is converted
into heat during braking
because of the friction of
your brakes against your
wheels and your tires
against the road.
…but worn or over-inflated
tires will reduce the friction
between your tires and the
road surface, reducing the
traction you need to:
(a) start smoothly
(b) stop quickly, and
(c) pull out of a turn or curve
without losing control
Friction
…also, road surface
changes due to: ice, rain,
snow, oil or fuel, sand and
dirt will reduce the traction
of your tires.
This could result in you
losing control of your
vehicle.
…skidding while braking is caused by the friction of your
brakes being stronger than the friction force between your
tires and the road, which causes you to lose traction.
Friction
…also, road surface
changes due to: ice, rain,
snow, oil or fuel, sand and
dirt will reduce the traction
of your tires.
This could result in you
losing control of your
vehicle. SLOW DOWN IN
THESE CONDITIONS.
…also if they become too hot, they cannot release any
more heat and will fail to absorb any more kinetic energy,
(as when traveling down a steep hill & using your brakes a lot)
The brakes may fail!
Friction
…locked wheels cannot
convert kinetic energy into
friction in your brakes as
the car continues to skid.
The purpose of anti-lock
brakes is to prevent your
wheels from locking
during a quick stop so
your brakes can absorb
energy and you can
maintain traction.
Centrifugal Force
Centrifugal force is the tendency for objects to be
pulled outward when rotating around a center.
Centrifugal Force
- In a turn, your
car is subject
to centrifugal
force which is
pulling your
car away from
the direction
you want to
turn and into a
straight line.
Centrifugal Force
Banked roadways
help in overcoming
the centrifugal force
that is pulling you
away from the
direction in which you
want to turn.
…to counteract the centrifugal force of a vehicle
in a turn you should:
(a) decelerate before the curve
(b) brake gently and gradually while turning
(c) downshift (manual transmission)
There are many different
types of tires for various
road and weather
conditions…
Tires
To avoid skidding, blowouts, and
unsafe handling, the manufacturer’s
recommendations for your vehicle
should be followed in selecting
replacement tires.
The recommendations for tire
pressure should also be
followed. Either under or over
inflated tires:
(a) reduces traction, increases
the likelihood of skidding, and
degrades the handling
characteristics of a vehicle, and
(b) leads to rapid tire wear.
In addition, failing to
maintain proper wheel
balancing and
suspension alignment
can lead to extreme
rapid tire wear and may
result in a blowout.
Tires
In addition, worn components
in the suspension and steering
systems of your vehicle can
cause you to lose control as
well as accelerate tire wear.
True or False: Most passenger
vehicle tires should be rotated
between 9600-16,000 kilometers.
The purpose of rotating tires
is to prolong the life of the tires.
It should be done according to
the intervals and procedures
recommended by the
manufacture of your vehicle
Another cause of poor tire wear is peeling out or spinning your
tires on fast starts. This behavior can also waste fuel, is potentially
dangerous, and can lead to a citation for “exhibition of speed”.
Checking
Tire Pressure
(check at every fuel fill up)
• To check your tire pressure
What
first unscrew
the air cap
do you
off of the tire
rim.
• Then use aknow
pressure gauge
to check your
tire pressure
about
and compare
it to the sticker
checking
on the inside of the door.
tire
• If your tire pressure is low,
pressure?
you should add air to your
tire as recommended.
Checking
Tire Pressure
• Some newer cars
will alert you when
your tire pressure is
low by displaying it
on the dash board.
• It is also a very
convenient way to check
your tire pressure.
Checking
Tire Pressure
Benefits of Proper Tire Inflation:
- optimal tire life (even wear of tires)
- better gas mileage
- more comfortable ride
Forces in a Crash
In any crash:
(a) the kinetic energy of your vehicle and
body must be dissipated.
(b) the forces needed to dissipate this
energy are lower if the time period over
which your vehicle moves during the crash
is longer.
(c) if the car suddenly stops, the forces will
be high.
Forces in a Crash
The forces that stop your car during a crash will
be greatest if you have a head-on collision with
another vehicle or large immovable object, such
as a bridge abutment, wall, or a tree because the
momentum and kinetic energy of your car must
be absorbed almost instantaneously.
Forces in a Crash
If two vehicles collide at the same rate of speed, the
vehicle that weighs less will take the greater impact.
The larger and heavier the vehicle, the greater the
energy of momentum. The smaller and lighter vehicle
may even be pushed in the reverse direction. In some
cases, the smaller and lighter vehicle may be crushed
as in: (a) a semi-truck against a sedan, (b) train against
a semi-truck.
Forces in a Crash
You can reduce the forces on
you and your car during a
unavoidable crash if you are
able to redirect your path toward
objects that will cause your car
to stop over a greater distance,
such as: bushes instead of
trees, snow, soft dirt, and sand
barrels placed in front of freeway
abutments.
Forces in a Crash
The purpose of barrels
filled with sand in front of
an abutment (such as a
support for a highway
overpass) is to reduce the
forces on your vehicle, by
allowing your vehicle to
travel farther than if it hit
the abutment directly.
Forces in a Crash
These features absorb energy during a crash and
increase the distance over which the impact occurs.
These include:
(a) Crush zones (areas of the vehicle designed to to absorb
the impact by crushing in without harming the passenger area
of the vehicle)
(b) I-beam construction in the frame and doors to
give the vehicle more rigidity
(c) Air bags (which allow the momentum of your body to be
absorbed over a greater distance than if it hit the steering wheel
or windshield)
Forces in a Crash
These features absorb energy during a crash and
increase the distance over which the impact occurs.
These include:
(d) Energy-absorbing bumpers that reduce the effect of the
kinetic energy during a front or rear-end collision.
(e) Padded dashboards, and (f) Safety glass windows and
windshields designed to crumble into small dull-edged pieces to
reduce lacerations.
If the force of impact is excessive, such as during a
head-on collision, the above safety features may still
not be enough to prevent serious injury.
Forces in a Crash
End of Natural Forces
Quiz time…how much do you remember?
1)1) It is important to understand the_______of_________ as
they significantly affect your ability to control your vehicle.
1)2) True or False: Gravity is the force that pulls objects
toward the center of the earth. It affects speed on hills.____
1)3) True or False:_______. When you are going downhill
the force of gravity will cause you to go faster. You must
compensate by shifting to a lower gear, or braking.
1)4) The greater the speed the ___________ the distance
needed to stop the vehicle.
1)5) True or False: Because of gravity, your kinetic energy
decreases when going up a hill, making it easier to stop
__________
6) You may be injured because of the inertia and
momentum of loose objects that become airborne during
________________
1)7) Wearing a ____________ while driving will stop the
forward momentum of your body if you have a collision.
1)8) True or False: If you are hit from behind while stopped,
you can experience a __________. A properly adjusted
headrest can minimize this injury. _________
1)9) ___________ energy is the energy a body possess
because it is in motion.
1)10) True or False: Kinetic energy is usually absorbed by the
brakes or engine compression in a controlled stop______.
1)11) If kinetic energy is not absorbed by the brakes or engine
compression, it must be absorbed by your vehicle or _____
______.
12) True or False: Going down a hill (gravity) with your
speed increasing will increase the kinetic heat energy that
must be absorbed. _______.
1)13) Momentum is the force of a moving object. The
momentum of an object is proportional to its ________
and _______.
1)14) True or False: Friction is the force caused by contact of
one surface upon another, resulting in resistance of an
object moving over a surface. _____.
1)15) During braking, the friction between the tires and road
and within the brakes converts into _______.
1)16) True or False: Changes in road surface (ice, rain or
snow) will increase the traction of your tires to the road.
______
1)17) Centrifugal force is the tendency for objects to be
pulled ________ when rotating around a center.
18) To counteract centrifugal force on a non-banked curve,
it is important to ____ _____ before entering the curve.
1)19) True or False: The forces that stop your car in a head-on
crash are greatest if you hit a immovable object (tree)
because the momentum and kinetic energy of you car must
be absorbed almost immediately. _____
1)20) You can reduce the force upon you and your car in a
crash if you can _______ your path toward objects such as
bushes, snow, & sand barrels to help absorb kinetic
energy.
1)21) Energy absorbing bumpers, padded dashboards and
safety glass are features which _________ the distance
over which the impact occurs, hopefully minimizing injury.
22) The best protection you have against injury if involved
in an collision is your ______ _____.
End of Natural Forces
Drivers Edge: Interactive slides and videos®
Copyrighted Driver Education School Literature
These electronic slide shows are produced by InterActive Enterprises.
Microsoft PowerPoint ® was used to create the presentations. Each segment includes
discussion questions and may include illustrations, photographs, videos, animations, etc.
Contact us at for more information at: 2183 Doctor Robertson Rd. Spring Hill, TN 37174
Email with suggestions, comments, questions or for more information.
This slide show is a type of educational media and is copyrighted in regards to slide
layout, text and arrangement. See other restrictions in regards to graphics as required by
agreements with graphic providers. RESTRICTIONS: “This product/publication includes
images from Microsoft Design Gallery, Animation Factory, Corel MegaGallery and Corel Gallery
1,000,000 and Click Art which are protected by the copyright laws of the U.S., Canada and
elsewhere. Used under license. These images are for viewing purposes only in this series and may
not be saved or downloaded for other uses.
Other images used by permission are from: In-Motion magazine, General Motors; selected videos
from the U. S. Dept. of Transportation (Moving Safely Across America) Many other images are from
the public domain.
A limited warranty or guarantee is in effect upon initial receipt of this product. Any defective product will be
replaced upon notification within 90 days of receipt of product.
Copyright © 2009 InterActive Enterprises
iae@charter.net