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
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