1. Natural Laws and Car Control
Chapter 9
Natural Laws and Car Control

2. Key Idea
This chapter describes how the laws of motion affect the ability of drivers to control their vehicle.

3. Gravity and Energy of Motion
Terms to Know:
Inertia
Momentum
Energy of Motion (KE = ½mv2)
Double the weight?
Double the Speed?
Gravity
What does it feel like to be a passenger in a car that stops suddenly? Has it ever happened to you when you were not wearing a seatbelt? What happened?
How about being in a car that accelerates suddenly?
Inertia – The tendency of an object at rest to stay at rest, and of an object in motion to stay in motion. From the Latin word for idleness - “iners”
Momentum – The tendency of an object in motion to stay in motion. From the Latin word for movement – “movere”
Energy of Motion – Kinetic Energy or the energy an object has because it is moving. KE = ½mv2
Gravity – Force that pulls all things to Earth.
Video 1 – About inertia (1:33 long)
Video 2 – (13:33 long) Covers Momentum, Inertia, and Force of Impact concepts

4. Tires and Traction Friction Traction Tread Inflation
Besides tires, what is another system in your car that uses friction?
Tread
Purpose of tread?
Inflation
Underinflation
Overinflation
Friction – The force of resistance that acts between materials moving past one another, which keeps tires from sliding on the road.
Traction – The resulting friction between the road and the tire. Answer to question: Brakes
Tread – Grooved surface of a tire. Purpose: starting, stopping, and gripping the road. Ability to grip road increases as amount of tread touching the road increases. Same as tread on a shoe. How is traction affected when you wear shoes with good tread? Poor tread? No tread?
Underinflation – Not enough air; Tire collapses on itself, only outer tread touches ground.
Overinflation – Too much air; tire bulges and only inner tread touches ground.
Temperature – Check tires when cold to make sure the pressure is ok to drive.

5. Using Traction Used to brake, accelerate, and steer.
Splitting traction between braking and steering can cause loss of control.
Ensuring Good Traction
Vehicle Condition
Road Condition
Ideal Setting
Driver Action
Ensuring Good Traction:
Vehicle Condition – Maintain good tire pressure, shock absorbers, and steering system.
Road Condition – Dry, paved, flat, straight
Driver Action – smooth, deliberate steering, braking and accelerating. Avoid “jerky” motions.

6. Other Terms to Know Vehicle Balance Center of Gravity Pitch Roll Yaw
What happens if you raise C. of G.?
Lower C. of G.?
Pitch
Roll
Yaw
These motorcycles are exhibiting which of the following: pitch, roll, or yaw?
Vehicle Balance – the distribution of a vehicle’s weight on its tires as they contact the ground.
Center of Gravity – Point around which an object’s weight is evenly distributed.
Pitch – Tilting motion from front to back.
Roll – Side to side motion.
Yaw – Rotating clockwise or counterclockwise. If tires lose traction in a turn or a curve this can cause a spin.

7. Forces Effecting Your Control in Curves
Sharpness of the curve
Speed
Load
Shape of the Road
Level
Crowned
Banked
Sharpness of the Curve – the sharper the curve the more traction needed to negotiate the curve. Sharper curve = slower speed
Speed – the faster you go the more traction needed to overcome your momentum. Slow before entering a curve/turn.
Load – Passengers, cargo and trailers can all effect load which also cause changes in center of gravity. This changes the handling of the vehicle. Slow before entering the curve.
Shape of the Road –
Level Road – Flat roadway = ideal for driving
Crowned Roadway – Helps rain drain away from the road and prevents flooding on roads, but increases traction requirements in a curve because gravity is pulling car towards the outside of the road.
Banked Roadway – One side higher than the other. Gravity is working to help keep you on the road in a banked curve.

8. Total Stopping Distance
1) Perception Time & Distance
What can effect perception time & distance?
2) Reaction Time & Distance
3) Braking Time & Distance
Perception Time & Distance – The amount of time and distance traveled while identifying a hazard, predicting a conflict, and deciding to brake. Perception Time for alert drivers is approximately ¾ of a second. Perception Time & Distance can be effected by visibility conditions, driver condition, driver alertness, and line of sight.
Reaction Time & Distance – The amount of time and distance covered while you execute your decisions (move foot from gas to the brake). An alert driver’s reaction time is approximately ¾ of a second.
Braking Time & Distance – The amount of time and distance covered from when your brakes are first applied to when your car comes to a stop. Braking requires space and time because you need to overcome Energy of Motion. Remember that braking distance is proportional to the square of your speed. A car traveling at 50 mph has 4x’s the braking distance than a car traveling at 25 mph.

9. Factors That Affect Braking Distance
Driver Ability
Speed
Vehicle Condition
Roadway Surface
Hills
Antilock Braking System
Weight/Load of the Vehicle
Driver Ability – Focused vs. Unfocused, new vs. experienced, drunk/drugged vs. sober, alert vs. fatigued, etc.
Speed – double your speed = 4x’s the stopping distance.
Vehicle Condition – well maintained vs. poor maintenance. Brakes, tires and shocks especially important.
Roadway Surface – Ideal: dry, paved, flat, straight vs. any change in one or more of those ideal conditions.
Hills – Up vs. Down hill
Antilock Braking System – Prevents wheel lock up and skids. Skidding = loss of traction and lengthens stopping distance.
Weight/Load – weight is directly related to stopping distance; more weight = longer stopping distance

10. Force of Impact Speed Weight Distance Travelled After Impact
Speed – the faster you the greater the force of impact and the slower you the lower the force of impact. Double your speed = 4 x’s the force of impact
Weight – the heavier the vehicle the greater the force of impact and the lighter the vehicle the lower the force of impact. Double your weight = double your force of impact
Distance Travelled After Impact – The greater the distance travelled the lower the force of impact and the shorter the distance travelled the greater the force of impact.

11. Restraint Devices and Other Protective Devices
Active Restraint Device
Passive Restraint Device
Child Safety Seats
Rear facing
Forward facing
Booster seat
Back seat
Crush Zones
Energy Absorbing Bumpers
Side-Impact Panels
Penetration-Resistant Windshields
Head Restraints
Active Restraints – Seatbelts – something the driver/passengers have to engage.
Passive Restraints – Airbags – a device that works automatically.
Keep hands at 9:00/3:00 or 8:00/4:00 so airbag pushes them down and away instead of into your face.
Child Safety Seats –
Rear Facing – Infants 1yr old or younger and 20 pounds or under
Forward Facing – Child more than 1yr old and over 20 pounds
Booster seats should be used for children until they are between 8-12yrs old because they do not fit children properly
All children younger than 13 should sit in the back seat
Crush Zones – Front ends and back ends are designed to crumple or crush down to absorb force of impact
Energy Absorbing Bumpers – designed to absorb low levels of impact (under 5 mph) w/o damage
Side-Impact Panels – Reduce the risk of passenger injury by decreasing the chance of objects penetrating the passenger compartment
Penetration-Resistant Windshields – thin layer of plastic in between sheets of glass prevent glass from the windshields flying into the passenger compartment
Head Restraints – Designed to prevent whiplash. Must be adjusted properly to prevent injuries though.

12. For Your Quiz You should be able to:
List the four factors that affect your vehicles control in a curve
Explain how center of gravity affects the handling of your car
List and explain the three parts of total stopping distance
List the factors that affect your braking distance
List and explain the three factors involved in Force of Impact
Explain how gravity affects your vehicle on a roadway