The Speed Factor: Negotiating Curves and Braking

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

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 4 1 2 3

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 • Kinetic Energy • 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 typeand 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? • 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 • 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