Driver's Education Part 4-5

Sir Isaac Newton

(1643-1727) was an English Scientist, he discovered - The Law Of Inertia - The Universal Law of Gravitation - The Law of Motion and Acceleration - The Law of Reciprocal Action

KEY POINT!

*KE = 1/2 MV2 or Kinetic Energy = one-half the Mass times Speed (velocity) squared*

Formulas for Driving Success

- How fast am I going? ANSWER: Take your speed, add 1/2 your speed. The result is your speed in feet per second.

Formulas for Driving Success (Con.)

- How long will it take to stop? ANSWER: Take your speed, multiply it by 1/10 of your speed and divide it by two. The result is your stopping distance, after the brakes are applied, in feet. (S x 1/10S)/2 = SD (feet)

Formulas for Driving Success (Con.)

- How will it really take? ANSWER: Since it takes about one second to recognize a danger and then react to it, add the distance you travel in one second to the stopping distance to find the total distance, in feet, it will take to stop. (S + 1/2S) + (S x 1/10 S /2) = Total Stopping Distance (feet)

Wearing Seat belts (Correct)

- Snug - Properly Positioned

Formulas for Driving Success (Con.)

- What is kinetic energy and what effect does it have one me? Kinetic energy, or momentum affects all aspects of driving. To stop a moving vehicle, you must dissipate (get rid of) the kinetic energy through the friction of the brakes or by hitting another object (called the force of impact). KE = 1/2M x V^2 - Any increase in the mass (weight) of the vehicle will proportionately increase the KE. Doubling the mass will double the KE. - Any increase in the velocity (speed) of the vehicle will increase the KE by the square of the change in speed. Doubling the velocity will quadruple the KE. - By braking and reducing your speed in half, the KE is now only one-fourth (1/4) from what it was at your original speed.

Formulas for Driving Success (Con.)

- What is the coefficient of friction? This is the amount of traction provided by the "footprint" of the four tires in contact with the road. Four brand new tires, on a perfectly smooth surface, gives a CF of 1.0; on smooth, dry asphalt the CF is 0.9; on wet pavement or melted ice, the CF is only 0.35; frozen asphalt gives a CF of 0.20; and ice has a CF of only 0.05.

As you increase your driving speed, both your body and your vehicle acquire kinetic energy which eventually must be:

- absorbed by your brakes, engine compression forces, or other friction in a controlled stop absorbed by your body, your vehicle's body, and the objects you hit if you are involved in a crash. - Kinetic energy is present in both the vehicle and you. If the vehicle stops suddenly, you kinetic energy will keep you moving forward.

gravity decreases your kinetic energy when you are driving uphill and increases it when you are driving downhill. Therefore, gravity will make it:

- easier to stop your car if you are going uphill more difficult to stop your car if you are going downhill

The kinetic energy of your moving vehicle determines your ability to stop the car. In addition to the distance traveled due to your reaction time, your stopping distance will be:

- four times further if you increase your speed from 10 MPH to 20 MPH - 25 times further if you increase your speed from 10 MPH to 50 MPH

When you make a controlled stop, the momentum of your vehicle must be overcome by the:

- friction force of your brakes -friction force between your tires and the road - compression force of your engine

There are many natural forces acting on your vehicle, such as:

- gravity - inertia - momentum - kinetic and potential energy - friction centrifugal force

The friction of your tires can be altered by changes in the road surface. Road surfaces change due to:

- ice - rain - snow - oil and diesel fuel buildup - sand or dirt

This means:

- if you increase your speed from 10 MPH to 20 MPH, you are dealing with four times the amount of kinetic energy - if you increase you speed from 10 MPH to 50 MPH you have to deal with 25 times the amount of kinetic energy

Friction is:

- increased by the weight of your vehicle - decreased if your tires are over-inflated or under-inflated - decreased if the tires are worn smooth - affected by the material used to construct the road - affected by the condition of the surface of the road (including factors due to weather)

Wearing Seat Belts (Incorrect Ways)

- placement of the arm over the chest portion of the belt - belt being too loose - belt being twisted

The kinetic energy of everything increases with weight (mass) and the square of your speed. This includes:

- your body while it is in motion - the loose objects in the car - the car itself

Force of Impact (Con.)

1. Impact Force Is Highest A head on collision produces the highest impact force. If two identical vehicles are moving at 40 mph and collide, head on, the FOI would be the same as driving into a brick wall at 40 mph (not 80 mph, or adding the speed of both vehicles together, as some might intuitively, but incorrectly, suspect).

Force of Impact (Con.)

2. Impact Force Is High A T-Bone, or side-impact, collision is the next deadliest. Since the vehicles are moving in different directions, some of the FOI is dissipated in forward motion.

Force Of Impact (Con.)

3. Impact Of Force Is Medium A "sideswipe" collision reduces the FOI by spreading it to the sides of the vehicles, as well as opposing directions.

Force Of Impact (Con.)

4. Impact Force Is Small A rear-end collision produces a much smaller amount of FOI, since the impact is transferred to the car in front, which then also moves forward.

Banked Roadways

Banked Roadways improve your traction in turns. They help overcoming centrifugal force that is pulling you away from the direction in which you want to turn. In order to keep a vehicle in a turn without allowing centrifugal force to pull the car out, you should: - decelerate before the curve - brake gently and gradually while turning - downshift (manual transmission)

Stopping Distance

Because friction is increased by the weight of your vehicle, a fully-loaded truck has more stopping power than does an empty one because it is heavier. The weight helps to stop the vehicle by producing more friction between the tires and the road surface.

Centrifugal & Centripetal Force

Centrifugal force is the tendency for objects to be pulled outward when rotating around a center. When you make a turn, you car is subject to centrifugal force (inertia), which is pulling your car away from the direction you want to turn and into a straight line. *Traction is necessary to keep from losing control in a turn.*

"Park" placement on car

DOWNHILL - If you are parking facing downhill, you should always turn your front wheels towards the curb or side of the road. UPHILL (CURB) - If you are parking facing uphill and there is a curb, you should turn your front wheels towards the middle of the road and allow the vehicle to roll back against the curb. UPHILL (NO CURB) - If you are parking facing uphill and there is not a curb, you should turn your wheels toward the side of the road.

Inertia & Energy

EX: Vessels in space can move really far without much spent energy because there is very little air acting to slow them down. When you are waiting for a green signal on flat pavement at an intersection, you will not move unless you engage the engine or are otherwise pushed.

Driving Downhill

Gravity will cause you to go faster and increase your stopping distance.

Force of Impact

In a crash: - the kinetic energy of your vehicle and body must be dissipated - the forces needed to dissipate this energy are lower if the time period over which your vehicle moves during the crash is longer You can reduce the forces on you and your car during an unavoidable crash is you are able to redirect your path toward objects that will cause your car to stop over a greater distance, such as: - bushes rather than trees - snow - soft dirt - sand barrels placed in front of freeway abutments

Kinetic Energy

Kinetic energy is the energy a body possesses because it is in motion. EX: the potential energy had by a book on a table is converted to kinetic energy (motion) when it falls. The book lying flat on the floor does not have this same kinetic energy.

KEY POINT!

Maximum Tread Contact = Maximum Friction

Potential Energy

Potential energy is the energy that an object possesses because of its position or form. EX: a book on a table has the "potential" energy to fall to the floor, whereas a book that is already on the floor has the potential energy to "fall" towards the center of the earth.

Momentum

The force of a moving object is called momentum. The momentum of an object is proportional to its weight and speed. EX: A brick traveling at 10 MPH has more momentum (force) than a chunk of Styrofoam traveling at the same speed.

Driving Uphill

The force of gravity is working against you to slow you down

Friction Wear on Brake Pads

The friction on your brakes and clutch results in brake and clutch what. if used improperly, excessive wear to the brake pads and clutch can occur. To avoid this: - do not ride your brakes - do not drive with your clutch partially engaged - use your lower gears to slow the vehicle on downhill grades (downshift) * Friction can also cause friction on other parts of your vehicle such as the bearings & internal engine parts USE thin film of oil or grease*

Friction Example:

This could result in you losing control of your vehicle. Skidding while braking is caused by the friction of your brakes being stronger than the friction force between your tires and the road, which causes you to lose traction.

The Law Of Inertia

an object in motion, remains in motion, in a straight line, at a constant speed, until acted upon by an unbalanced force

Friction

is a force caused by the contact of one surface on another. It results in the resistance of an object moving over a surface. EX: it is easier to move you hand over fine sandpaper than over rough sandpaper because there is less friction.

Gravity

is the force that pulls all objects towards the center of the earth. EX: Gravity also affects your speed of travel when you're going uphill and downhill because of the change in gravitational pull as you move towards or away from the earth.

Traction

is the result of friction between the road and you tires caused by the weight (gravity effect) of car pushing the tires to the road due to gravity. EX: Traction is necessary for you to steer your car.

The Law of Gravitation

one object attracts another, via a straight line, drawn between the objects' center. The larger the mass the stronger the attraction