natural laws and car control chapter 9. laws of motion…. how do they affect your ability to...
TRANSCRIPT
NATURAL LAWS AND CAR CONTROLCHAPTER 9
Laws of Motion….How do they affect
your ability to drive??
Inertia Objects at rest tend to stay at rest and
objects that are moving tend to keep moving.
Inertia keeps this parkedcar parked.
Inertia keeps this movingcar and everything init moving until acted upon by another force.
driving around a curve. Inertia causes your body to continue in a
straight line.
As the car decelerates…
The force of friction on the brakes causes the car to slow down.
You feel this when you are pressed against your safety belt.
As the car accelerates rapidly…
you seem to be pushed back into your seat.
Momentum… Momentum is inertia in motion or the
tendency of an object to stay in motion. Momentum depends upon of speed and
weight of an object.
A heavy vehicle has more momentum than a light vehicle.
A fast car has more momentum than a slow car.
Energy of motion… is the kinetic energy of a moving object. It is the work needed to accelerate or
decelerate and object 15 feet stopping distance
25 miles per hour
60 feet stopping50 miles per hour distance A vehicle’s energy of motion is proportional to the
square of its speed. Double speed=4x as much energy Double weight=2X stopping distance
4X
Gravity…
Is the force that pulls all thinks to Earth.
When you drive uphill, thepull of gravity will cause you to losespeed. When you drive downhill, The pull of gravity will causeyou to go faster.
Tires and Traction
Even though you control your vehicle by using the steering wheel, accelerator, and brake pedal, your tires are a key part to your control system. Friction is the force that acts between
materials as they move past each other. Keeps a tire form sliding on the road
When tires run over the surface of the road they create a form of friction called traction.
Traction makes it possible for your vehicle to grip the road so that you can control speed and direction.
Acceleration causes the tires on the drive wheels rotate pushing you forward.
During deceleration, as the tires on the wheel slow, traction between the tires and the road will slow your vehicle.
Tire Tread and Traction Only four small areas underneath each
tire holds the vehicle on the road. This is called its footprint andare all you have for traction on thesurface of the road. Tread provides the traction forStarting, stopping, and gripping the road.
Inflation and Traction
Properly inflated tires can mean the difference between keeping or losing control.
Inflation and Traction continued… Underinflation will shorten the life of
the tire and will accept less stress before losing its grip on the pavement.
Overinflation of a tire will cause the tire to have a smaller footprint so the tire will have less traction.
Temperature can change the pressure in tires.
Colder weather causes pressure to drop.
Hot weather will increase pressure.
Using Traction Used to accelerate, brake and steer Even under ideal conditions, your tires
provide a limited amount of traction.
Traction continued… Braking hard and steering may
consume most of your traction in emergency situations.
Skidding is a result and you may lose control.
To regain control change traction forces by turning the wheel sharply in to curve.
Ensuring Good Traction Vehicle Condition
-Check tire pressure and tread often-Replace worn shock absorbers
Road Conditions-Good traction on dry, flat road-reduced traction on gravel, snow,
ice, leaves, sand and oil (REDUCE SPEED) Your actions affect your ability to
maintain traction so try to maximize your traction by steering, accelerating, and braking gently and smoothly
Vehicle Balance and Control In Curves
Your ability to control your vehicle is affected by its balance.
Vehicle balance is the distribution of a vehicle’s weight on its tires ads they contact the ground.
Only perfect when car is not moving
Center of Gravity Point around which an objects weight is
evenly distributed The lower the center of gravity, the
more stable the vehicle Taller, narrow vehicles with a higher
center of gravity tend to be less stable
Balance and Steering
Forces in Curves Factors affecting your ability to control
your vehicle in a curve1. Sharpness of curve- the sharper the curve, the more traction your tires need to grip the road in order to overcome inertia.2. Speed and weight of vehicle-The momentum of your vehicle increases speed. The faster you go, the more traction you need to overcome momentum. If you go to fast, your vehicle might not be able to make the turn.3. Shape of roadway
Stopping Distance When you have to stop quickly, you
must perceive the hazard in your path of travel, react, and brake to a safe stop.
Total Stopping Distance- distance your car travels from the time you first perceive a hazard until you reach a full stop.
Insert figure 8 here
Perception Time and Distance
PT
The length of time it takes you to identify a
hazard, predict a conflict, and decide to
break.
¾ second
PD
The distance your vehicle travels during your perception time
Varies depending upon visibility, alertness, and your line of sight.
Can improve perception time by using IPDE
12-15 seconds ahead
Reaction Time and Distance
RT The time from
identifying a hazard and applying the brake.
¾ second
RD The distance your
vehicle travels while you react.
Braking Distance The distance your vehicle travels from
the time you apply the brake until you stop.
It is proportional to the square of your speed
example- 40 mph… Is affected by driver ability, speed,
vehicle condition, roadway surface, hills, and the weight of vehicles load.
Controlling the Force of Impact
Force of Impact The force with which a moving object
hits another object. Three Factors determine the force of
impact
Speed A vehicle’s momentum is proportional
to its speed and weight. Higher the speed the more the damage Always try to reduce speed in an
emergency
Weight The heavier a vehicle, the more damage
it will cause in a collision. A vehicle weighing twice as much as
another vehicle will hit a solid object twice as hard.
Time Between Impact and Stopping
How quickly a vehicle stops affects the force of impact.
If a truck hits a stone wall, the force of impact is great because the collision occurs in a brief moment.
If the same truck hits a patch of bushes, the truck will come to a stop more gradually, and there will be less damage.
When a vehicle hit’s an object, inertia causes the driver and passengers to
continue forward until they hit either….the inside of the vehicle
ortheir restraint devices.
Restraint Devices
Active Must be engaged
by you Safety Belt
Passive Automatically
works Airbags
WEARING A SAFETY BELT IS YOUR FIRST DEFENSE IN AN EMERGENCY!!!
WHY????
Safety belts hold you in place and prevent you from being thrown from the vehicle.
Distributes the forces of rapid deceleration over larger and stronger parts of the body
(pelvis, chest, and shoulders)
Safety Belts continued…
Consist of lap belt and shoulder belt During a collision, the reels of the belt
will suddenly tighten up and hold you in place.
To Ensure Maximum Protection From Your Safety Belt…
Adjust you seat back to an upright position.
Click the belt’s latch in the buckle. Lap belts should be low and snug
across hips. Adjust shoulder belt snuggly across
chest and collarbone. NEVER wear it under your arm or
behind your back!!
Air Bags
Frontal Only deploy
when there is a crash in the front of the vehicle.
Side Designed to
protect your head and chest.
Protect from injury and from ejection during a rollover.
Using Airbags Effectively Designed to work with safety belts. So
make sure you always buckle up. Keep hands at 9 and 3 or 8 and 4. Seat needs to be at least 10 inches from
the hub of the steering wheel. Front passenger seats need to be back
as far as possible. The passenger side airbag is 2-3 larger than the driver’s.
Child Passenger Safety All states have laws that require proper
restraints for infants and children.
Infants 20 Pounds or Less Rear-facing car seat
20 Pounds and Over Forward-facing car seat
13 and Younger
Back seat riders
Other Protective Devices Crush Zones- front and rear ends absorb
force Energy Absorbing Bumpers- absorbs low
levels of impact without damage Side-Impact Panels-absorbs crash energy
and reduces the risk of penetrating objects Penetration- Resistant Windshields- made
with plastic between 2 layers of glass Head Restraints- Padded and protects
against whiplash