Transcript 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