Chapter 9Chapter 9Natural Laws and Car ControlNatural Laws and Car Control

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• 8 questions on page 181

• Mid-Term Friday August 22nd.

• Make sure you have your notebook!

Chapter 9Chapter 9Natural Laws and Car ControlNatural Laws and Car Control

OBJECTIVES:OBJECTIVES: Gravity & Energy of MotionGravity & Energy of Motion

Friction & TractionFriction & Traction

Stopping DistanceStopping Distance

Controlling Force of ImpactControlling Force of Impact

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.

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.

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 pedal).

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

Energy of Motion

Energy of Motion• When the weight and speed of a vehicle

increases, the stopping distance increases.

• 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 doubles – the stopping distance is about four times as long.

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!

http://video.google.com/videoplay?docid=-6824119360217412702&q=speeding+car+crash&total=268&start=0&num=10&so=0&type=search&plindex=2

Physical Forces that Influence Driver Control

At 60 mph you need about 303 feet to stop.

When speed doubles it’s about 4 times the stopping

distance as 30 mph.

At 30 mph and 3000lbsyou need 78 feet to stop.

At 30 mph and 6000lbsyou need 156 feet to stop.

When the weight doubles…stopping distance doubles.

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.

Friction and Traction

Friction• Is the force that keeps each tire from sliding

on the road. • You can feel this same force by rubbing

your hands together.

Friction and Traction

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.

Friction and Traction

Tires• Tires make a difference in the way your

vehicle performs.• Proper tire pressure can mean the

difference in avoiding a crash and hitting something.

Friction and Traction

Tires• 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.

Friction and Traction

Tires• 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

blowout.

Friction and Traction

Inflation• 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.

Friction and Traction

Inflation• Under Inflation: Only the outside edges of

the tire provide traction.• Split Traction: You are dividing your

traction between stopping, starting and turning.

• You have reduced traction based on the maneuver

Friction and Traction

Reduced Traction• Ideal levels of traction can be maintained

by:• Vehicle is in good mechanical condition.• The road must be smooth, paved, level,

and clean.

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.

Stopping Distance

• When you are driving and have to stop, three things must happen:• You must perceive the hazard in your

path of travel• React• Brake your car to a stop

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

Stopping DistanceTotal 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.

Stopping DistanceEstimating 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.

Stopping DistanceEstimating Stopping Distance1. Pick a fixed checkpoint

ahead where you think you could stop.

2. Count off four seconds: one-thousand-one, one-thousand-two, etc.

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

Controlling Force of ImpactForce of Impact

Speed: • 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 emergency.

Controlling Force of ImpactOther Protection Devices

• Engineers have designed additional devices in new vehicles to protect you:• Automatic Seat Belts• Front and Rear Crash Areas• Energy-Absorbing Bumpers• Side Door Beams• Reinforced Windshields• Energy-Absorbing Steering Wheel

Columns• Padded Dash• Child Seats• Head Restraints

Controlling Force of ImpactForce 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 itself.

• 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.

http://video.google.com/videoplay?docid=3937168886833428491&q=car+hitting+pole&total=124&start=0&num=10&so=0&type=search&plindex=8

Controlling Force of ImpactHow 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 seatbelt1. Adjust your seat to an upright position.2. Make sure your seatbelt is not twisted.3. Snap the buckle into place and tighten the

lap portion across your hips.4. Adjust the shoulder strap across your

chest. Make sure it is snug.