Natural Laws & Car Control

Chapter 5

Gravity

Gravity (Natural Law)– force that pulls all things to earth Driving Up Hill – acts against gravity

Naturally loose speed Must accelerate to maintain speed Braking distance shortened

Down Hill Naturally gain speed It will take longer to stop Braking distance will be longer Steeper the incline – longer the stopping

distance

Gravity

Center of Gravity Point around which an objects weight is evenly

distributed Automobile makers attempt to lower car’s center

of gravity so it handles better Higher the center of gravity = more unstable (see pg

92)

Kinetic Energy – energy in motion Object moves it picks up energy Faster = More energy More Weight = More energy of motion (kinetic

energy)

Energy of Motion

As speed & weight of a vehicle increases… More speed = longer distance to stop

Speed doubles = 4x more stopping distance (x2) Speed triples = ___ more stopping distance Speed quadruples = _____ more stopping

distance More weight = longer distance to stop

Weight doubles = Stopping distance doubles See picture pg 93

Friction & Traction

Friction – force that keeps each tire from sliding on the road

Traction – friction created by tires Makes it possible for tires to grip the road Traction allows the car to move, change speed, direction, etc.

Tread –created by grooves - grooved surface on tire Wet Road Conditions – allows water to flow through

the grooves away from the tire Hydroplaning - car floats on water – looses traction More tread on the road = more gripping = more control So… Tires play the most important role in

maintaining control

Tires

Bald Tires Little tread = little gripping = little control Dangerous especially on icy or wet roads Increase risk of blowouts - rapid loss of air pressure

Tire Inflation Each tire works best at certain air pressures Too much or too little changes the amount of tread

on the road Remember: More tread on the road = more control Also: Correct tire pressure = Better gas mileage

Tires roll easier at correct pressure

Tires & Inflation

Under Inflation – only outside edge of tire provides traction Outside edges wear first Will fail quicker

Over Inflation – only the center of the tire provides traction Center will wear out first

Temperature Colder = lower tire pressure Hotter = increase tire pressure

Check Tire pressure regularly before driving

Traction

Split Traction When braking & turning or braking & accelerating

Some traction is used for braking or accelerating Some traction is used for turning

2 Things Needed for Ideal Traction #1. Good Vehicle Condition

Tires, shock absorbers, steering system Worn shocks will cause car to bounce off the road Tire Treads – must have at least 1/16th of an inch

Penny Test – shouldn’t be able to see all of Lincoln’s head

#2. Good Road Conditions (Concern = Ice!)

Curves Energy of Motion (Kinetic Energy) will try to make

you go straight around a curve Faster = greater force to go straight

Vehicle Control in a Curve (4 factors) #1 Speed

Higher speed = less control Lower speed = more control Best Practice: Lower speed before entering a

curve #2 Sharpness of Curves

Sharper curve = more needed traction Best Practice: Sharper curve = slower speed

Curves

Vehicle Control in a Curve (4 factors continued)

#3 Banked Curves – higher on the outside vs inside

Helps to reduce vehicle’s tendency to move to the outside

#4 Load of the Vehicle Higher load = more kinetic energy Best Practice: Higher load , slower around

curves

Vehicles of Different Sizes & Power Handle Differently Smaller vehicle = generally stop & accelerate quicker

Stopping Distance

Total Stopping Distance Distance the Car travels while you make a stop Must do 3 things to stop

#1 Perceive the hazard #2 React #3 Brake

Perception Time Time it takes to Identify, predict & decide Varies based on

Visibility, the hazard & driver abilities

Perception Distance Distance vehicle travels during this time

Stopping Distance

Reaction Time Length of time it takes to execute action Average driver’s reaction time = ¾ of a second Reaction Distance

Distance vehicle travels while you react

Braking Distance Distance vehicle travels from the time you apply

the brakes until the vehicle stops Remember: Faster = longer stopping distance (x2)

Example: 40 mph will have a 4x longer braking distance than 20mph

Stopping Distance

Also see page 98

Estimating Stopping Distance

4 Second Rule – used to estimate stopping distance Pick an object on the road ahead where you think you

can stop Count 4 seconds Check vehicle position

Note: It will take you 300’ (football field) to stop going 65 mph

Factors That Affect Braking Speed – faster = longer braking distance Vehicle Condition -worn tires/shocks = longer braking

distance

Factors Affect Braking

Roadway Surface – rain/snow/gravel = longer BD

Driver Ability – distracted or impaired = longer BD

ABS - Can better stop your vehicle while turning

Hills – Uphill = shorter / Downhill = longer

Loads – Heavy Loads = longer BD

Controlling Force of Impact

Force of Impact – force generated when one moving object hits another

3 Factors Determine “Force of Impact” Speed – increase or decrease in speed

squares the force of the impact Weight of Vehicle – heavy vehicle =

greater force of impact Distance between Impact and stopping –

Hit something that doesn’t “give” = greater force of impact

Seat Belts & Air Bags

3 Collisions Occur in a Crash Vehicle hits object Occupants hit the inside of the vehicle Body organs (brain, heart, liver) hit skeleton

Restraint Devices - holds occupant in place Passive Restraint – works automatically –

occupant doesn’t have to do anything (Ex. Airbag)

Active Restraint – device you have to engage (Ex. Seatbelt) Wear it properly

Air Bags

Deploy at 200 mph

Designed to work with seat belts Most air bags are only effective with front collisions Seat Belts help in side/ rollover etc. Keep hands at 9 & 3 Sit Back – chest should be 10 “ away Children in child seats and children under 12 must

sit in back seat

Advancements Sensors for weight and position in seat Switch to turn off

Supplemental Devices

Front or Rear End crushes on impact

Energy absorbing bumpers

Side door beams

Reinforced Windshields

Energy absorbing steering columns

Padded Dash

Child Safety Seats – back seat – required in all states

Head Restraints