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Natural Laws and Vehicle Natural Laws and Vehicle ControlControl
Chapter 9Chapter 9
Driver EducationDriver Education
Legacy High SchoolLegacy High School
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Gravity and the Energy of MotionGravity and the Energy of Motion
• There are many natural laws such as gravity, speed and momentum that exert forces on a vehicle.
• Many times these forces are great enough to cause a driver to lose control.
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Gravity and the Energy of MotionGravity and the Energy of Motion
• To be a safe driver, you need to know about these natural laws and the effect they can have on your ability to safely control a vehicle.
• You cannot change the natural laws, you can have better control of your vehicle with knowledge of these laws.
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Gravity and the Energy of MotionGravity and the Energy of Motion
• Gravity – gravity keeps your vehicle on the ground.
• Gravity makes going up hill difficult and increases downhill speed.
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Center of GravityCenter of Gravity
• The center of gravity is usually located at the center of your vehicle and is the point where the vehicle’s weight is evenly distributed.
• When a vehicle “rolls” it rotates around the center of gravity.
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• Raising a vehicles center of gravity could make it unstable on a steep hill or on a sharp turn.
• High profile vehicles have a higher center of gravity and may be involved in rollover accidents.
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Energy of MotionEnergy of Motion
• Once a vehicle is moving, it takes energy to stop.
• The heavier or faster a vehicle is, the longer the stopping distance.
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Energy of Motion – Stopping Energy of Motion – Stopping DistanceDistance
• A vehicles stopping distance doubles when its weight doubles.
• When a vehicle’s speed doubles, the stopping distance increases 4 times.– When a vehicle’s speed triples, the stopping
distance increases nine times. (the square rule)
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Centrifugal forceCentrifugal force
• Centrifugal force is the tendency for an object to continue to move in a straight line when the object changes direction.– A vehicle turning left
wants to continue forward, this is why passengers are “forced” to lean to the right.
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Centrifugal forceCentrifugal force
• If a vehicle loses traction (tire grip on the road), centrifugal forces can cause the vehicle to run off the road.
Questions on Gravity and the Energy of Motion
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Friction and TractionFriction and Traction
• The tires and their contact with the road surface control the direction and speed of a vehicle.– It is these four small areas of contact that give
vehicle control.
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Friction and TractionFriction and Traction
• Friction is the force that keeps each tire from sliding on the road.– Friction gives your vehicle control.
• Another term used for friction when speaking about vehicles and tires is traction.
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Tires and TreadTires and Tread
• Tread – the grooved surface on a tire that allows water or snow to flow through the grooves and away from the tire.
• Traction is increased as is vehicle control when water is channeled away from the tire.
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Tires and TreadTires and Tread
• A worn or bald tire is dangerous and will not grip a wet or icy road.
• Bald tires have no tread and may suddenly deflate if the tire is punctured – a blowout.
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Tires – Inflation and TractionTires – Inflation and Traction
• Each tire has inflation and other specifications.
• Use tires designed for your vehicle and type of driving you may do.
• Specific tread types may function better in rain or snow.
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Tires Underinflation Tires Underinflation
• When driving on an underinflated tire, only the outside edges of the tire are in contact with the road surface.
• The outside edges wear first.
• Will not perform properly in an emergency and will heat and fail prematurely.
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Tires -- Tires -- OverinflationOverinflation
• If a tire has too much air pressure, only the center of the tire will grip the road and will wear out first.
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Tires -- InflationTires -- Inflation
– Outside air temperature can change the air pressure in tires.
• Cold temperatures decrease pressures• Hot temperatures increase pressures.
– All tires “leak” a small amount of air.– Check tire pressures on a monthly basis.– Inspect tires for tread wear and inflation every
time you enter the vehicle.• Inspect for cracks or tire damage.
– Check tire pressures when the tires are “cold” – before you start driving.
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Tread depthTread depth
– Ideal levels of traction are maintained when tires have good tread depth and are properly inflated.
– When using a tread depth gauge, tires need to have at least 1/16-in. of tread or more (this is the minimum amount of tread allowed by law).
– By using a penny as a quick reference, insert the penny into the tread groove with Lincoln’s face showing, but with his head upside-down. If you are able to see all of Lincoln’s head, the tire needs replacement.
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HydroplaningHydroplaning
• A wedge of water in front of the tires may pass under the tires and the tires will ride on a cushion of water.
• Traction will be lost completely.
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Road surfaceRoad surface
• Wet or icy road surfaces will reduce traction, giving the driver less control and increasing stopping distances.
• Rough, gravel, or dirt road surfaces have less traction than paved surfaces.
• Oil on the road surface can mix with water or rain causing decreased traction.
• Always slow down when traction is decreased.
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CurvesCurves
• The vehicle’s speed, the sharpness of the curve, the bank of the curve, the road condition and the vehicle’s load will affect the control you have in a curve.
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CurvesCurves
• You have no control over how sharp a curve is, or road condition, but you can control your vehicle’s speed.
• Reduce your speed before entering the curve.– If you cut your speed in
half, the force pushing you off the road will be cut four times.
Friction and Traction Questions
