Chapter 9 Natural Laws and Car Control Gravity

Chapter 9 Natural Laws and Car Control

Gravity and Energy of Motion Lesson 9. 1

The Laws of Motion �Inertia �Momentum �Energy of Motion �Gravity

Inertia �Objects that are at rest tend to stay at rest objects that are moving tend to keep moving. �A parked car stays at rest. For cars to move, they must be acted upon by forces produced by the engine.

You can feel inertia when a car brakes rapidly. As the car slows down, inertia causes your body to continue to move forward. How does inertia affect your body when a car accelerates rapidly? What causes that effect? How does inertia affect you when a car drives around a sharp curve? What causes that effect?

Momentum �Tendency of an object to stay in motion, or the inertia of an object in motion �The amount of momentum depends upon the object’s weight and speed �Does the truck or car have the most momentum?

A moving object also has ENERGY OF MOTION, or kinetic energy, that changes in proportion to the weight of the vehicle.

� A vehicle’s energy of motion is proportional to the square of its speed. � Double your speed and your vehicle will: �have four times as much energy of motion �need four times as much distance to

Gravity �The force that pulls all things to Earth �Act on your car �Lose or gain speed How can you control speed if you were driving on this downhill stretch?

Tires and Traction Lesson 9. 2

Friction Traction �The force that acts �Makes your vehicle between material as they move past each other �How can you feel the force of friction by rubbing your hands together? grip the road so you can control speed and direction.

The traction of the tires on the roadway pushes your vehicle forward. Braking causes the friction of the brake linings against the brakes to slow the wheels. Traction between the tires and road will slow your vehicle. Traction also enables your vehicle to turn left or right when the front wheels turn.

The grooved surface of a tire is called tread �Tread provides the traction for starting, stopping, and gripping the road. Tread helps prevent skids and hydroplaning.

Tire Tread and Traction �The place where a tire touches the road is called its footprint. This picture shows the red patch under the tires that form the footprint. �These small footprints are all you have for traction on the road surface.

Imagine you enter this curve at 55 mph. As you reach the middle of the curve, you realize you are going too fast, so you quickly brake and turn the wheel sharply into the curve. What would

Ensuring Good Traction �Three things are required to achieve ideal levels of traction. �vehicle condition �road surface �driver actions

MINUTE TO WIN IT!

�Take a piece of paper, cut in half to share with someone around you �Write down 3 ideas that relate to this game and driving.

Hydroplane

Understanding Tire Inflation Cold air makes tire pressure drop, and tires can become underinflated. *The Car will use more energy while driving Hot temperatures will increase pressure, and may cause overinflation. � size of its footprint in contact with the road is reduced. � could be damaged more easily when running over potholes or debris in the road.

Vehicle Balance and Control in Curves Lesson 9. 3

Vehicle Balance �The distribution of a vehicle’s weight on its tires as they contact the ground � Where would the balance point be on each of these two cars?

Stability �A vehicle with a center of gravity that is close to the ground is more stable and less likely to roll over than one with a high center of gravity. �Which of these three vehicles is less likely to roll?

Center of Gravity

Balance and Steering �Maneuvers that can shift weight to different areas of the vehicle cause changes to the vehicle’s balance. �Imagine three axes crossing at the center of gravity. �Your vehicle may rotate around these axes in three ways: � pitch � roll � yaw

Pitch �A tilting motion from front to back is called pitch. �Where does the weight shift occur when braking? �Where does the weight shift when accelerating?

Yaw “Fishtale”

Shape of the Road The shape of the roadway affects your ability to control your car. Many roads are level. Some roads have a crowned surface. What is the benefit of a crowned surface? Why is it more difficult to maintain traction if a Some roadways are banked, or tilted so one side is higher than the other. What is the benefit of making a curve banked?

I got jokes �Anne meets up with Dana while she is picking up her car from the mechanic. �Anne asks, "Everything ok with your car now? " �Dana replies, "Yes, thank goodness. I was worried that my mechanic might try to rip me off, so I was relieved when he told me all I needed was $12 worth of blinker fluid. "

Stopping Distance Lesson 9. 4

Total Stopping Distance �The distance your car travels from the time you first perceive a hazard until you reach a full stop is your total stopping distance. • You should always be able to stop within the distance you can see ahead. • It will take you almost 300 feet, or the length of a football field, to stop if you are traveling at 65 mph.

Perception Time and Distance �The length of time it takes you to identify a hazard, predict a conflict, and decide to brake is your perception time. �Perception time for alert drivers is about three fourths of a second. �The distance your vehicle travels during your perception time is your perception distance. �What factors can affect your perception time? �How can you improve your perception time?

Reaction Time and Distance �Once you identify a hazard, the length of time you take to apply the brake is your reaction time. �An alert driver’s reaction time is about three fourths of a second. �The distance your vehicle travels while you react is called your reaction distance. The distance your vehicle travels from the time you apply the brake until you stop is your braking distance.

FACTORS THAT AFFECT BRAKING DISTANCE What is the most efficient way to stop? Why? Factors that can affect your total braking distance include: • driver ability • speed • vehicle condition • roadway surface • hills • weight of the vehicle’s

I got jokes �A traffic cop pulled alongside a speeding car on the motorway. Glancing into the car, he was astounded to see that the young lady, who was driving, was knitting. �Realizing that she was oblivious to his flashing lights and siren, the policeman wound down his window, turned on his loudspeaker and yelled, 'PULL OVER!' �'NO', the young lady yelled back, 'IT's A SCARF!'

Controlling Force of Impact Lesson 9. 5

Force of Impact � The force with which a moving object hits another object is called force of impact. � Three factors determine the force of impact: � speed � weight � time between initial impact and stopping

Force of Impact