1. Chapter 9 Natural Laws and Car Control
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8 questions on page 181
Chap. 8 answers 1.a,2.c,3.c,4.a,5.d,6.d,7.d
Mid-Term Mon. 8/22/16
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2. Chapter 9 Natural Laws and Car Control
OBJECTIVES:
Gravity & Energy of Motion
Friction & Traction
Stopping Distance
Controlling Force of Impact

3. Gravity and Energy of Motion
Gravity and energy of motion are both natural laws that will effect the way your vehicle performs.
When you operate a small vehicle, like a bicycle, it is easy to control it because of the low speed and weight.
A car or SUV can weigh as much as two tons (4,000 lbs)!!
Natural Laws can create forces that work against you in emergency situations.

5. Gravity and Energy of Motion
Gravity is the force that pulls all things to the earth.
Gravity pulls your car towards the earth when you are driving.

6. Gravity and Energy of Motion
You can feel the pull of gravity as you drive up and down hills.
When you drive uphill, you will lose speed unless you use extra power (gas pedal).
If you want to maintain the same speed, you must increase the power to overcome the force of gravity.

7. Energy of Motion Energy of Motion
When the weight and speed of a vehicle increases, the stopping distance increases.
If the weight doubles – the stopping distance doubles.
The stopping distance will change in proportion to the square of its change in speed. When the vehicles speed doubles – the stopping distance is about four times as long.

8. Energy of Motion Energy of Motion Speed Kills!!
We all understand the dangers of speeding.
You will develop an ability to adjust to traffic situations ahead of time. You will see how important it is to slow before an emergency situation develops.
Every time you cut your speed in half, you cut your energy of motion by four times!

9. Physical Forces that Influence Driver Control
At 30 mph and 3000lbs
you need 78 feet to stop.
At 30 mph and 6000lbs
you need 156 feet to stop.
When the weight doubles…
stopping distance doubles.
At 60 mph you need
about 303 feet to stop.
When speed doubles it’s about 4 times the stopping distance as 30 mph.

10. Friction and Traction
Your four tires are the most important factor in controlling your car.
In reality, your car makes tracks similar to an animal walking in the mud or snow.
Each footprint is approximately twice the size of your hand.

11. Friction and Traction Friction
Is the force that keeps each tire from sliding on the road.
You can feel this same force by rubbing your hands together.

12. Friction and Traction Traction
The friction created by the tire on the road is called traction.
Traction makes it possible for your vehicle to grip the road so you can change speed and direction.

13. Friction and Traction Tires
Tires make a difference in the way your vehicle performs.
Proper tire pressure can mean the difference in avoiding a crash and hitting something.

14. Friction and Traction Tires
The grooved surface of a tire that grips the road is called the tread.
When the road is wet the tread allows water to flow through the grooves.
This action allows the tire tread to cut through the water and grip the road.

15. Friction and Traction Tires Warn or bald tires are dangerous.
A bald tire will not grip a wet or icy road.
Since it has no tread to push the flow of water away from the ground.
It is also more vulnerable to a puncture or blowout.

16. Friction and Traction Inflation
Tires are designed to work best when they are properly inflated.
Check the owner’s manual for best pressure to use.
When your tire pressure is right, you will get the best control from your tires.

17. Friction and Traction Inflation
Under Inflation: Only the outside edges of the tire provide traction.
Split Traction: You are dividing your traction between stopping, starting and turning.
You have reduced traction based on the maneuver

18. Friction and Traction Reduced Traction
Ideal levels of traction can be maintained by:
Vehicle is in good mechanical condition.
The road must be smooth, paved, level, and clean.

19. Friction and Traction Vehicle Condition
The older your vehicle – the more important it is to properly maintain it.
Good shocks are necessary to prevent your vehicle from bouncing.
Worn tires limit your control.

20. Stopping Distance
When you are driving and have to stop, three things must happen:
You must perceive the hazard in your path of travel
React
Brake your car to a stop
The distance your car travels while you make a stop is called your Total Stopping Distance.

21. Total Stopping Distance
Total Stopping Distance is the distance your car travels while you are attempting to stop it.
The picture on Page 98 shows the distance it take once you see a hazard to the point where you stop your vehicle.

22. Estimating Stopping Distance
The chart on page 99 shows your reaction distance and braking distance from different speeds.
Use the four second rule, which enables you to project your approximate stopping distance under ideal conditions at any speed.

23. Estimating Stopping Distance
Pick a fixed checkpoint ahead where you think you could stop.
Count off four seconds: one-thousand-one, one-thousand-two, etc.
Check your vehicles position. If you have just reached your fixed checkpoint, you can assume the distance you estimated in step 1 was correct.

24. Controlling Force of Impact
Speed:
The most important factor in determining how hard a vehicle will hit another object.
The force of impact is in proportion to the square of the increase or decrease in the vehicle’s speed.
Any reduction in speed will greatly reduce the damage inflicted.
Always try to reduce speed in an emergency.

25. Controlling Force of Impact Other Protection Devices
Engineers have designed additional devices in new vehicles to protect you:
Automatic Seat Belts
Front and Rear Crash Areas
Energy-Absorbing Bumpers
Side Door Beams
Reinforced Windshields
Energy-Absorbing Steering Wheel Columns
Padded Dash
Child Seats
Head Restraints

26. A 18-year-old was killed when she veered off the left shoulder of the roadway and overcorrected on I24. Her car struck a tree in the driver’s side door.

28. Controlling Force of Impact
Distance Between Impact and Stopping:
The distance a vehicle covers between the instant it hits an object and the moment it comes to a stop can vary greatly.
Image hitting barrels filled with sand sitting in front of a light post rather than hitting the post itself.
The barrels will slow you as you hit them rather than stopping you like the post would.
This is why traffic engineers put cushioning materials in front of solid roadside objects.

29. Distance Between Impact and Stopping

32. Controlling Force of Impact
How to Wear Safety Belts
Using safety belts is the #1 defense to reduce possible injury.
They hold you in place and prevent you from being thrown from the vehicle.
Follow these steps with your seatbelt
Adjust your seat to an upright position.
Make sure your seatbelt is not twisted.
Snap the buckle into place and tighten the lap portion across your hips.
Adjust the shoulder strap across your chest. Make sure it is snug.