NATURAL LAWS & DRIVING It doesn’t matter what kind of vehicle you own or how skilled a driver you are, these forces affect your driving. Learning to understand natural forces is the only way to be able to safely control a car during turns, stops, rounding curves and while driving in bad weather conditions. Being aware of these forces will help you be prepared for emergency situations and avoid collisions.

Gravity The force that pulls all objects towards the center of the earth. Driving uphill, gravity acts to slow your car. Acceleration will maintain speed. Driving downhill, gravity tends to speed up your car. Braking will slow it down.

Center of Gravity The point around which all the weight of an object is evenly distributed The lower an object’s center of gravity, the more stable the object. Changes in the car’s center of gravity affects how well the car handles Vehicles with high centers of gravity are less stable and difficult to control on turns, curves, and during sudden changes in braking, acceleration, and direction.

Center of Gravity

It is important to understand the effect of gravity when parking your car on an incline. You already know that gravity will try to pull the parked vehicle down. So your goal is to park in manner that will prevent the vehicle from rolling away.

Friction Resistance to motion between two objects when they touch Friction tries to make the surface of your tires “stick” to the surface of the road. Your car must overcome friction in order to move. Your car, however, stays on the road because a certain amount of friction is always present.

Traction Traction (Adhesion): Friction between the road and your tires. What are some factors that affect traction?

Factors that affect Traction Tire pressure: For best traction, inflate the tires to the pressure recommended by the manufacturer Under inflating your tires will have only the outer edges gripping the road Over inflating your tires will have only the centers contacting the road Tire condition: Bald tires –tires with very little or no tread- provides almost no traction on wet, icy, or snow-covered roads. On dry roads, bald tires reduce directional control and are more apt to puncture Rain: Water provides a smooth surface for the tires to move across which does not provide good traction. If tires are properly inflated and have a good tread, much of the water will go into the grooves between the treads. Therefore, the treads will come in contact with less water and more road surface.

Factors that affect traction Ice and snow: Traction is poorest near 32 degrees F, when snow and icy become a slippery, watery slush Snow tires help to increase traction on snow, but not necessarily on ice Chains help increase traction on ice, but provide poor traction on pavement Studded tires can help on ice but are not as effective as chains All-weather tires are a good choice Road condition: Rough roads and potholes make your car bounce up and down, reducing traction. Wet leaves also reduce friction.

Momentum Momentum: The product of weight and speed. If either the weight or speed of a vehicle increases, so does the vehicle’s momentum. The greater the momentum, the greater the damage in a collision.

Inertia The tendency of an object in motion to stay in motion and for an object at rest to stay at rest. If you brake the car hard, everyone will tend to keep moving forward. Loose books and materials on the seat also continue to move forward. Always use seat belts…secure all loose objects.

Inertia Inertia keeps your vehicle moving until some force slows it down or stops it. This force can be your own action of applying a brake, the conditions of the road, an object on the road like fallen tree or, if the driver isn’t paying enough attention, even another vehicle.

Centrifugal Force The force that pushes a moving object out of a curve and into a straight path Inertia keeps a vehicle moving in a straight path. You must overcome the effects of inertia by turning the steering wheel. You will feel as though you are pulled toward the door into the curve, this is centrifugal force pushing you in the direction opposite to the way you are turning.

Energy of Motion Kinetic Energy: The energy of motion. The faster a car moves, the more energy of motion it has. The more energy of motion a car has, the more time and distance it will take to stop. Greater the weight of the vehicle, longer it takes to accelerate. Need to manage time and space differently to compensate for extra weight Due to the increase in the car’s momentum and kinetic energy, its stopping distance also increases.

Force of Impact The force with which a moving object hits another object. When two vehicles moving at the same rate of speed are involved in a collision, the vehicle that weighs less will take the greater impact; the larger and heavier the vehicle, the greater the energy and momentum. The smaller and lighter vehicle will have greater deceleration and may even be pushed in the reverse direction of travel.

Force of Impact 3 factors that determine how hard the vehicle will hit another object Speed- Most important factor determining force of impact. Weight Distance between the impact and the stop (Hitting tree/Hitting hedge)

Unbelted persons in a collision cannot protect themselves against the force of impact. Without the seat belt restraint system, they will hit the car interior or anything in their way with a tremendous amount of force.

Roadways Banked Curve- Higher on the outside than on the inside. Where would you find these? Crowned Roadway- Higher in the center Where would you find these and why?

Skids Braking- apply brakes to hard and wheels lock. Power- Suddenly press the accelerator to hard. Cornering- Lose steering control in a turn, curve, or lane change Blow out- when tire suddenly looses air pressure.

3 Factors that Cause Skidding Traction was reduced Tried to change speed to quickly Tried to change direction to quickly

Stopping Perception time and distance Reaction time and distance Braking distance Total stopping distance