Chapter 9

Chapter 9Natural Laws and Car Control

Key IdeaThis chapter describes how the laws of motion affect the ability of drivers to control their vehicle.

Gravity and Energy of MotionTerms to Know:InertiaMomentumEnergy of Motion (KE = mv2)Double the weight?Double the Speed?Gravity

What does it feel like to be a passenger in a car that stops suddenly? Has it ever happened to you when you were not wearing a seatbelt? What happened?

How about being in a car that accelerates suddenly?

Inertia The tendency of an object at rest to stay at rest, and of an object in motion to stay in motion. From the Latin word for idleness - iners

Momentum The tendency of an object in motion to stay in motion. From the Latin word for movement movere

Energy of Motion Kinetic Energy or the energy an object has because it is moving. KE = mv2

Gravity Force that pulls all things to Earth.

Video 1 About inertia (1:33 long)

Video 2 (13:33 long) Covers Momentum, Inertia, and Force of Impact concepts3Tires and TractionFrictionTractionBesides tires, what is another system in your car that uses friction?TreadPurpose of tread?InflationUnderinflationOverinflation

Friction The force of resistance that acts between materials moving past one another, which keeps tires from sliding on the road.

Traction The resulting friction between the road and the tire. Answer to question: Brakes

Tread Grooved surface of a tire. Purpose: starting, stopping, and gripping the road. Ability to grip road increases as amount of tread touching the road increases. Same as tread on a shoe. How is traction affected when you wear shoes with good tread? Poor tread? No tread?

Underinflation Not enough air; Tire collapses on itself, only outer tread touches ground.

Overinflation Too much air; tire bulges and only inner tread touches ground.

Temperature Check tires when cold to make sure the pressure is ok to drive.4Using TractionUsed to brake, accelerate, and steer.Splitting traction between braking and steering can cause loss of control.Ensuring Good TractionVehicle ConditionRoad ConditionIdeal SettingDriver Action

Ensuring Good Traction:Vehicle Condition Maintain good tire pressure, shock absorbers, and steering system.Road Condition Dry, paved, flat, straightDriver Action smooth, deliberate steering, braking and accelerating. Avoid jerky motions.5Other Terms to KnowVehicle BalanceCenter of GravityWhat happens if you raise C. of G.?Lower C. of G.?PitchRollYawThese motorcycles are exhibiting which of the following: pitch, roll, or yaw?

Vehicle Balance the distribution of a vehicles weight on its tires as they contact the ground.

Center of Gravity Point around which an objects weight is evenly distributed.

Pitch Tilting motion from front to back.

Roll Side to side motion.

Yaw Rotating clockwise or counterclockwise. If tires lose traction in a turn or a curve this can cause a spin.6Forces Effecting Your Control in CurvesSharpness of the curveSpeedLoadShape of the RoadLevelCrownedBanked

Sharpness of the Curve the sharper the curve the more traction needed to negotiate the curve. Sharper curve = slower speed

Speed the faster you go the more traction needed to overcome your momentum. Slow before entering a curve/turn.

Load Passengers, cargo and trailers can all effect load which also cause changes in center of gravity. This changes the handling of the vehicle. Slow before entering the curve.

Shape of the Road

Level Road Flat roadway = ideal for driving

Crowned Roadway Helps rain drain away from the road and prevents flooding on roads, but increases traction requirements in a curve because gravity is pulling car towards the outside of the road.

Banked Roadway One side higher than the other. Gravity is working to help keep you on the road in a banked curve.7Total Stopping Distance1) Perception Time & DistanceWhat can effect perception time & distance?2) Reaction Time & Distance3) Braking Time & Distance

Perception Time & Distance The amount of time and distance traveled while identifying a hazard, predicting a conflict, and deciding to brake. Perception Time for alert drivers is approximately of a second. Perception Time & Distance can be effected by visibility conditions, driver condition, driver alertness, and line of sight.

Reaction Time & Distance The amount of time and distance covered while you execute your decisions (move foot from gas to the brake). An alert drivers reaction time is approximately of a second.

Braking Time & Distance The amount of time and distance covered from when your brakes are first applied to when your car comes to a stop. Braking requires space and time because you need to overcome Energy of Motion. Remember that braking distance is proportional to the square of your speed. A car traveling at 50 mph has 4xs the braking distance than a car traveling at 25 mph.8Factors That Affect Braking DistanceDriver AbilitySpeedVehicle ConditionRoadway SurfaceHillsAntilock Braking SystemWeight/Load of the Vehicle

Driver Ability Focused vs. Unfocused, new vs. experienced, drunk/drugged vs. sober, alert vs. fatigued, etc.

Speed double your speed = 4xs the stopping distance.

Vehicle Condition well maintained vs. poor maintenance. Brakes, tires and shocks especially important.

Roadway Surface Ideal: dry, paved, flat, straight vs. any change in one or more of those ideal conditions.

Hills Up vs. Down hill

Antilock Braking System Prevents wheel lock up and skids. Skidding = loss of traction and lengthens stopping distance.

Weight/Load weight is directly related to stopping distance; more weight = longer stopping distance9Force of ImpactSpeedWeightDistance Travelled After Impact

Speed the faster you the greater the force of impact and the slower you the lower the force of impact. Double your speed = 4 xs the force of impact

Weight the heavier the vehicle the greater the force of impact and the lighter the vehicle the lower the force of impact. Double your weight = double your force of impact

Distance Travelled After Impact The greater the distance travelled the lower the force of impact and the shorter the distance travelled the greater the force of impact.10Restraint Devices and Other Protective DevicesActive Restraint DevicePassive Restraint DeviceChild Safety SeatsRear facingForward facingBooster seatBack seatCrush ZonesEnergy Absorbing BumpersSide-Impact PanelsPenetration-Resistant WindshieldsHead RestraintsActive Restraints Seatbelts something the driver/passengers have to engage.

Passive Restraints Airbags a device that works automatically.

Keep hands at 9:00/3:00 or 8:00/4:00 so airbag pushes them down and away instead of into your face.

Child Safety Seats

Rear Facing Infants 1yr old or younger and 20 pounds or under

Forward Facing Child more than 1yr old and over 20 pounds

Booster seats should be used for children until they are between 8-12yrs old because they do not fit children properly

All children younger than 13 should sit in the back seat

Crush Zones Front ends and back ends are designed to crumple or crush down to absorb force of impact

Energy Absorbing Bumpers designed to absorb low levels of impact (under 5 mph) w/o damage

Side-Impact Panels Reduce the risk of passenger injury by decreasing the chance of objects penetrating the passenger compartment

Penetration-Resistant Windshields thin layer of plastic in between sheets of glass prevent glass from the windshields flying into the passenger compartment

Head Restraints Designed to prevent whiplash. Must be adjusted properly to prevent injuries though.11For Your QuizYou should be able to:List the four factors that affect your vehicles control in a curveExplain how center of gravity affects the handling of your carList and explain the three parts of total stopping distanceList the factors that affect your braking distanceList and explain the three factors involved in Force of ImpactExplain how gravity affects your vehicle on a roadway