- Gravity (its effect on time and space management) - Kinetic and potential energy - Friction and centrifugal force - Factors that affect stopping ability - Forces of Impact

This lesson will deal with how the laws of nature affect your ability to control your vehicle.

The laws we’ll consider are:

These forces affect how your vehicle handles so you may react appropriately in emergency situations.

Let’s first think about gravity.

If you break the laws of nature or misjudge them while driving you may end up losing

control and get into a collision.

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.

The Law of Gravity: time and space management

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.

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?

80km/h

REACTION DISTANCE BRAKING DISTANCE STOPPING DISTANCE

55 to 65 meters

The greater the speed, the greater the distance needed to brake the vehicle to a stop.

80km/h

100km/h

REACTION DISTANCE BRAKING DISTANCE STOPPING DISTANCE

REACTION DISTANCE BRAKING DISTANCE STOPPING DISTANCE

55 to 65 meters

75 to 92 meters

Obviously following too closely can result in a rear end collision…drop back to increase following distance

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…

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.

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.

Check to see that it is

properly adjusted

Kinetic Energy

Momentum Momentum is the force

of a moving object. The momentum of an object is proportional to its weight and 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.

For example, a baseball traveling at 16 km/h has more momentum (force) than a ping

pong ball traveling at the same speed.

Momentum

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.

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.

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.

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.

For example, it is easier to move your hand over writing paper than over rough sandpaper because there is less friction.

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.

…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.

This could result in you losing control of your vehicle.

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)

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.

There are many different types of tires for various road and weather conditions…

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.

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”.

True or False: Most passenger vehicle tires should be rotated

between 9600-16,000 kilometers.

Tires

Checking Tire Pressure

(check at every fuel fill up)

• To check your tire pressure first unscrew the air cap off of the tire rim.

• Then use a pressure gauge to check your tire pressure and compare it to the sticker on the inside of the door.

• If your tire pressure is low, you should add air to your tire as recommended.

WhatWhatdo youdo youknowknowabout about

checkingcheckingtiretire

pressure?pressure?

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checkingcheckingtiretire

pressure?pressure?

Checking Tire Pressure

• It is also a very convenient way to check your tire pressure.

• Some newer cars will alert you when your tire pressure is low by displaying it on the dash board.

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

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