Vehicle and Road Safety/Natural Laws (8.1-8.2)
Friction and Traction Safe Skills:
-Drive more slowly and carefully on rough or wet roads, and increase your space cushion to five seconds or more. -Make sure your tires are in good shape—that they have adequate tread and are inflated properly, and equally. -Your brakes and other parts of your car, including your engine and transmission, should be properly lubricated.
Inertia Safe Skills:
-Always use your seat belt, and require your passengers to do the same. If they won't, don't let them ride with you. An unbelted passenger can become a lethal projectile in a crash. -Don't leave objects in the cabin of the car that might fly around and injure someone in the event of a crash—put them in the glove box or trunk instead.
Gravity Safe Skills:
-Check your speed and adjust accordingly to maintain control on hills, perhaps switching to a lower gear on very steep hills. -Make sure to use the parking brake when you park on an incline. -When facing downhill, turn your wheels toward the curb. If your car rolls, gravity will pull it into the curb, and it will stop. When facing uphill, turn your wheels away from the curb. If your car rolls, gravity will pull it into the curb, and it will stop. -If there is no curb, turn your wheels away from the street. If your car rolls, gravity will pull it away from the street, rather than into traffic.
The Forces at Work on the Road:
In this lesson, you'll learn about how some key natural laws affect your car in various situations, and how you can prepare or maneuver accordingly to stay safe.
Gravity:
The apparent force of gravity is equal to the weight of the object itself, so a typical car is affected roughly 20 times more strongly by gravity than a human.Gravity adds to your momentum when driving downhill, and subtracts from it when driving uphill. When you park on a hill, think about which way gravity is pulling your vehicle. Make sure your parking brake is engaged and your wheels are aligned properly to keep you from rolling into traffic.
Inertia:
The law of inertia states that an object in motion will stay in motion, and an object at rest will stay at rest, unless acted upon by an outside force. Although you might feel at one with the machine when you drive, you and your vehicle are different objects. If you're driving even as slow as 15 mph and slam on the brakes without your seat belt buckled, you'll go flying! At greater speeds, even gentle braking can throw you out of your seat if you're not buckled up. Airbags are meant to cushion properly-restrained occupants, not protect people hurtling through the cabin. In a crash, your seat belt is the only thing keeping you from being ejected through the windshield. It's not just the driver's responsibility: an unbuckled passenger becomes a cannonball in a crash, and can cause serious injury or death even if the driver is buckled up and protected by airbags.
Force of Impact:
Force of impact is the force generated when objects meet. It depends on the kinetic energies of the colliding objects, and the distance or time over which the impact occurs. Force of impact is one of the primary factors determining the severity of a collision. Why does defensive driving involve so many instances of "slowing down"? It's a well-known fact that the faster you drive, the greater the impact or striking power of your vehicle. What's not as well-known is that force of impact doesn't just increase at the same rate as speed—it increases exponentially! That's because it's based on kinetic energy. Remember: double your speed and you quadruple your kinetic energy. So, if you double your speed, you also quadruple the force of impact. At ten times the speed, the force of impact is 100 times greater! Today's automobiles are equipped with many features designed to absorb energy and decrease the force of impact. Front and rear crash areas, energy-absorbing bumpers, side door beams, reinforced windshields, energy-absorbing steering wheels, padded dashes, head restraints, airbags, and seat belts help by increasing the distance over which the impact occurs, increasing the time over which the impact occurs, or both. Remember, auto safety features are useless if you don't play your part by buckling up and driving defensively!
Friction and Traction:
Friction is the resistance of movement between two surfaces in contact. Friction occurs between your tires and the road, in your brakes when applied, and in many parts of your car. If it weren't for friction, you couldn't start, move, turn, or even stop your car in an emergency. Friction is a way of controlling or transmitting energy. When you put your foot on the accelerator, the friction between your tires and the road is what transmits the power of your engine to the ground, resulting in forward motion. When you put your foot on the brake pedal, the friction of your brakes absorbs your vehicle's energy, slowing you down. When your tires transmit your car's energy to the ground through friction, that's called traction. Traction is the gripping power of the tire as it rolls over the roadway. For good traction, you need enough rubber on your tires, and a road surface that isn't slick with rain, oil, leaves, ice, or any other slippery substance. The type or condition of the road surface greatly influences how much traction you'll have. Dry, concrete roads provide the best traction, while dirt roads or wet roads provide poor traction. On dirt roads, your tires are literally rolling over small stones that produce a ball bearing effect—like trying to walk on marbles. As a result, you need a lot more space to stop on a dirt road than you do on dry pavement.
Kinetic Energy Safe Skills:
-Kinetic energy always interacts with other forces, like gravity. When driving uphill, it is much easier to stop your car as opposed to driving downhill, as gravity is slowing you down on the uphill, and speeding you up on the downhill. Because the force of gravity is equal to the weight of an object, the weight of your car will also affect its stopping distance.
Force of Impact Safe Skills:
-Slow down to reduce kinetic energy and force of impact. -Always use your seat belt and require your passengers to do the same. -Don't leave objects in the cabin of the car that might fly around and injure someone in the event of a crash.
Prepared for Anything:
As important as it is to plan ahead, sometimes you can't stop things from going wrong. A nail on the road, a leaky engine, and unexpected cold snap making the ground freeze. Those are examples of what you can't stop from ever happening, but you can prepare yourself to deal with them calmly. As you have learned so far in the course, most collisions don't happen as a result of bad karma, or bad luck, nor can they be described as accidents. We also know that the majority of collisions are preventable through good defensive driving habits. And since we have the power to reduce our risk of a crash or other emergency, that means we also have the responsibility to do so. Reducing risk requires a basic understanding of how physics affect a motors vehicle. When you understand the interplay between gravity, inertia, kinetic energy, and traction, you'll be able to better able to control your vehicle, and have more respect for the factors that determine the severity of a crash. You'll also benefit from knowing the nuts and bolts that keep your car in one piece and running smoothly. Everyone experiences a vehicle breakdown at some point, why not equip yourself with a little knowledge, and save some time, money, and worries? The same goes for safe driving in storms and other severe weather events. Knowing when it's safe to go, and went to turn around, could save your life. Finally, even if you've done all you can to reduce grass, some crashes or other emergencies are unavoidable. But if you plan ahead, you'll feel empowered when disaster strikes. And if you keep calm, you can handle any situation with confidence.
Kinetic Energy:
When a vehicle—or any other object—is in motion, it has kinetic energy. Kinetic energy (KE) is given by the equation KE = 1/2mv², where m is the object's mass and v is the object's velocity. As an object in motion becomes heavier, its kinetic energy increases proportionally: double the mass and you double the kinetic energy. But as an object in motion speeds up, its kinetic energy increases exponentially: double the velocity and you quadruple the kinetic energy. This is why a tiny bullet traveling at high speed does so much more damage than a huge truck bumping into something at 1 mph.So, what does this mean for you behind the wheel? Whenever your vehicle slows down, it has to overcome, or dissipate, its kinetic energy. Normally, you accomplish this through the brakes: your car's kinetic energy turns into heat energy from the friction of your brakes. That's why braking distance increases exponentially as speed increases—twice the speed means four times the braking distance.But in a crash, that kinetic energy is dissipated through the force of the impact. That's why the likelihood of injury or death increases exponentially as speed increases—twice the speed also means four times the force of impact. Out of everything you learn today, this might be the most important lesson: the best way to reduce the severity of a crash is to reduce your speed. Kinetic energy always interacts with other forces, like gravity. When driving uphill, it is much easier to stop your car as opposed to driving downhill, as gravity is slowing you down on the uphill, and speeding you up on the downhill. Because the force of gravity is equal to the weight of an object, the weight of your car will also affect its stopping distance.
Natural laws:
•gravity •inertia •kinetic energy •friction and traction •force of impact