1. The Speed Factor: Negotiating Curves and Braking
Chapter 6
The Speed Factor: Negotiating Curves and Braking

2. 6.1 Physical Laws That Affect Driving
Speed
Refers to how fast something is moving/How quickly position is changing over time
Measured in m/h or km/h
Acceleration
Measures the rate of change of an objects speed
Increasing speed over a given period=acceleration
Decreasing speed over a given period=deceleration

3. Example…
A car is traveling from point A to point E. At the beginning of point A, you are traveling 0mph. At the end of point C you are traveling 60mph. When you reach point D you are still traveling 60mph. When you stop at point E, you are traveling 0mph. A B C D E
Starting Point 1 2 3 4

4. Gravity
Force exerted by massive objects on another object to “attract”, or “pull” toward its center
In terms of driving:
When traveling uphill, gravity pulls your car towards the ground causing you to use more power for the engine to maintain speed
When traveling downhill, it requires less power because you are moving in the direction that gravity is pulling you

5. Traction
Friction between your vehicle’s wheels and the surface of the road
Necessary to move, change direction, and stop
Keeps control of your vehicle
Traction increases when the amount of tire tread touching the road increases

6. Tread The grooved surface of the tire that grips the road.
Water flows through the grooves
1/16 inch tread
Police used a penny to test tread depth

7. Inflation and Traction
Check owner’s manual for best pressure
When pressure is right, you get your best control, better gas mileage, and tire wear.
Under-inflation
Over-inflation
Split Traction

9. Reduced Traction Two things to maintain ideal levels of traction
Vehicle must be in good condition
Tires, shock absorbers, steering system
Road must be smooth
Snow, Ice, Rain, Gravel

10. Reduced Traction

11. Torque Ability of a force to cause an object to rotate
In driving terms, it is the engine’s ability to apply more force to turn your wheels
When the force applied to your wheels exceeds the force resisting(traction), your wheels WILL spin

12. Inertia An object in motion stays in motion
An object at rest will remain at rest
Unless acted upon by a force
Examples of inertia:
Accelerating
Decelerating/Braking
Turning
Crashing

13. Kinetic Energy and force of Impact
The energy an object in motion has
For a vehicle to stop, it must lose kinetic energy
Braking
Coasting
Impact
Force of Impact
The force of a collision as determined by the magnitude of kinetic energy of the objects that collide and the distance over which the kinetic energy is lost
Softer objects spread have more “give” and will spread the force of impact over a greater distance
3 Factors
Speed
Weight
Distance between impact and stopping

14. Reducing Force of Impact
Guard Rail
Dashboards
Bumpers
Body of Car
Air Bags

15. 6.2 Negotiating Curves Centrifugal Force
The outward force or “pull” experienced when traveling in a circular path
In terms of driving, the inertia of your body attempting to continue traveling in a straight line as the vehicle changes direction

16. Center of Gravity (COG)
Point at which an object’s weight is centered
Vehicles that are wide have a lower COG
SUVs and Jeeps have higher COG
Vehicles with higher COG have higher potential to roll or flip on sharp turns

17. Loading
Adding weight to your vehicle’s weight as measured when it is empty
Can affect a vehicle’s COG
You are loading your vehicle anytime you get in the car
Increased loading will cause your vehicle to work harder

18. Road Slopes
Level
Banked
Crowned

19. Banked Road
Dips down in one direction so that one side is higher than the other
Dips in the direction of the curve to reduce loss of traction
Reduces incidence of rollover
Some are banked the wrong way, must be aware

20. Crowned Roads Higher in the center than the sides
Promote runoff to reduce hydroplaning
Can help or harm you, depending on the direction of travel

21. Entering a Curve SPEED is only thing we can control
Must reduce speed before entering the curve
Reducing during the turn is extremely dangerous
Road conditions
Should be a last resort
Maintain lane position
Do not understeer or oversteer
Slow in, Fast out
Brake going into the turn and accelerate out

22. 6.3 Braking
How to brake
Get to know how “touchy” the brakes are before you begin driving at high speeds
Keep heel of right foot on the floor
Move from accelerator to brake without lifting foot

23. Anitlock Braking Systems (ABS)
Sensors mounted on each wheel that determines whether the wheel locks or stops rotating during braking
Sensor sends a signal to the microprocessor that controls the brakes
Microprocessor tells the brakes to release enough pressure on that particular wheel to allow it to skid
The microprocessor then tells the brake to increase pressure
This is repeated many times a second
You may feel a “pulsing” sensation

24. Emergency Braking E-Brake Pumping the brakes For vehicles without ABS
If done on a vehicle with ABS, it can send false information to the sensors and can cause the car to skid

25. Stopping Distance
Strong correlation between the speed you are traveling and the time required for you to stop.
Your ability to stop smoothly, accurately, and rapidly depend on two things:
Reaction distance
Distance traveled by your vehicle during the time it takes you to identify the need to stop
Depends on speed, visibility, and your mental and/or physical state
Faster you are moving and the harder it is to see, the longer it takes to react
Braking distance
Distance needed to come to a complete stop once the brakes have been applied
Depends on vehicle type and weight, type and wear of tires, and condition of brakes

26. Reaction distance + Braking distance =
Stopping distance
Total distance required to stop from the first time you recognize the need to brake to the time the vehicle is no longer moving
SPEED is the most important factor
The faster you go, the longer it takes to stop

27. 6.4 Speed Limits What is a safe driving speed? Posted Speed Limits
Factors that affect “safeness”:
Posted speed limits, weather conditions, visibility, surface condition of the roadway, traffic conditions, lane width, and any special speed laws (depends on the type of vehicle you are driving)
Posted Speed Limits
Maximum speed limit
Not there to recommend a driving speed
Minimum speed limit
Prevent drivers from moving at such slow speeds that they impede or block the normal flow of traffic

28. Basic Speed Law Everyone has one
It says that a driver should operate his/her vehicle at a speed that is reasonable for existing conditions
Examples would include inclement weather, poor visibility, poor traffic conditions, or poor roadway surface

29. Other Speed Laws Uniform Speed Zones Special Speed Laws
Provide speed limits in commonly encountered locations even where no max. or min. speed limits are posted
School zones
Railroad crossings
Alleys
Business districts
Residential districts
Rural highways
Interstate freeways
Special Speed Laws
Slow moving vehicles
Trailers
Trucks or tractors with three or more axles