1. 1 Natural Laws and Vehicle Control Chapter 9 Driver Education Legacy High School

2. 2 Gravity 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.

3. 3 Gravity 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.

4. 4 Gravity and the Energy of Motion Gravity – gravity keeps your vehicle on the ground. Gravity makes going up hill difficult and increases downhill speed.

5. 5 Center 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.

6. 6 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.

7. 7 Energy of Motion Once a vehicle is moving, it takes energy to stop. The heavier or faster a vehicle is, the longer the stopping distance.

8. 8 Energy of Motion – Stopping Distance 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)

9. 9 Centrifugal 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.

10. 10 Centrifugal force If a vehicle loses traction (tire grip on the road), centrifugal forces can cause the vehicle to run off the road. QuestionsQuestions on Gravity and the Energy of Motion

11. 11 Friction 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.

12. 12 Friction 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.

13. 13 Tires 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.

14. 14 Tires 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.

15. 15 Tires – 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.

16. 16 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.

17. 17 Tires -- Overinflation If a tire has too much air pressure, only the center of the tire will grip the road and will wear out first.

18. 18 Tires -- 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.

19. 19 Tread 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.

20. 20 Hydroplaning 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.

21. 21 Road 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.

22. 22 Curves 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.

23. 23 Curves 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