Drivers Ed

Centripetal force

(which means center-seeking force) pulls an object towards the center of a curve.

Your vehicle is affected whenever you perform one or more of the basic vehicle control tasks:

Acceleration shifts the center of vehicle gravity to the rear of the vehicle, causing the front to lift, and reducing front wheel traction. Braking shifts the center of vehicle gravity to the front of the vehicle, causing the back to lift and decreasing back wheel traction. Steering towards the left or right shifts the vehicle's center of gravity in the opposite direction.

Newton's First Law states:

An object at rest will remain at rest unless acted upon by an outside force. An object in motion will remain in motion unless acted upon by an outside force. This law expresses the principle of inertia. Inertia affects the most basic operations of your car, including starting and stopping.

Gravity is a force that attracts any two objects to one another. The strength of this force depends on the mass of the objects and the distance between the objects. The more mass two objects have, or the closer two objects are, the stronger the force of gravity between them will be.Mass is a measure of the amount of matter that makes up an object.

An object's mass is a product of its volume (how much space the object takes up) and its density (how tightly matter is packed in the object). In practical terms, an object's mass is very similar to its weight.

Antilock brakes are designed to prevent this problem. Think of antilock brakes as a hand that slows a spinning wheel by grabbing it very briefly over and over again until it stops.

As long as regular brakes are fully depressed, they continue to clasp the wheels until they stop spinning. Antilock brakes, however, apply smaller amounts of pressure repeatedly to make sure the wheels slow down at the same rate as the car. If the wheel seems about to lock up, the brakes release some pressure until it's safe to apply more.

When responding to rear wheel traction loss:

As you lose traction, continue looking towards your intended destination. Do not look towards the side of the road. Ease your foot off of the brake or accelerator pedal so that your car's weight will become more balanced. Allow your car's wheels to roll and regain traction. As your car rolls, it may travel away from your intended path. When the skid stops, your car's momentum will tend to shift in the opposite direction. Be prepared to steer appropriately in response. Continue to steer cautiously until you have reentered your intended path. If you steer too sharply, the rear of your car may swing back and forth. Accelerate gradually to transfer weight to the rear.

Centripetal and centrifugal forces influence the shape of the curve a car moves in. Turning your steering wheel angles the front wheels of your car in the direction you intend to travel.

Centripetal force is created by the friction between the road and the tires on these angled front wheels, which pulls your car in the direction of the turn. The sharper the angle of the wheels and the more friction between your tires and the road, the greater the centripetal force will be, and the tighter a turn you will be able to make.

If you realize that a collision with another vehicle or a stationary object is immediate and unavoidable, you can minimize the force of impact by:

Decreasing your speed or steering your car in a way that gives you more time to slow before hitting the object Directing your car towards objects more able to absorb the force of impact, such as bushes or sand barrels on expressways, instead of concrete barriers or other vehicles Driving your car towards surfaces such as snow or soft dirt that can cushion the impact Diverting your car so it collides with another car or object from the side rather than head-on to lessen the severity of the impact

Newton's Third Law: Action and Reaction Newton's Third Law states:

For every action, there is an equal and opposite reaction. The basic significance of this principle is that a force never acts on a single object alone, but always involves an interaction between a pair of objects. For instance, the force necessary to propel your car is generated when your spinning tires and the solid pavement push against each other.

Skids and collisions are often the result of the deadly combination of speeding and the inability to control your car's balance:

If balance is shifted too quickly, the force of the weight transfer may be stronger than the force of traction between your wheels and the road, causing your car to skid. If the force of traction resists the force of the weight transfer, your vehicle may roll over.

Leaves on the road can be especially dangerous when it's raining.

In the fall, leaves on the ground may even cause the same problems that occur when driving on ice. Slow down by braking gently and continue driving slowly until you reach a stretch of the roadway that is clear.

Any sudden shifts will cause your tires to lose traction unevenly, affecting the consequences of the maneuver. For example, if a rear tire has less traction than the corresponding front tire, that tire will begin to slide sideways towards the front tire and cause a spinning action.

Keep in mind that these problems will be exacerbated by the condition of your tires. If your tires are unevenly worn or inflated, every situation will become more dangerous—and you will not have traction or the ability to control your vehicle when you most need it.

To decrease the risk of rear wheel traction loss:

Make sure your rear tires have at least as much tread depth as your front tires. Make sure you are driving with the correct amount of tire pressure. If you only purchase two tires at a time, put the new tires on the rear axle and move the tires on the rear axle to the front.

Steering affects a vehicle's side-to-side balance. A vehicle's weight will shift to the left or right side depending on its speed and the amount of steering input. This movement to the left or right is known as Roll.

Steering to the right will cause a vehicle to roll to the left, while steering to the left will cause a vehicle to roll to the right. This may be the easiest balance shift to feel with your kinasthetic sense. As you turn left, you will feel yourself lean toward the right.

Have you ever swung an object tied to the end of a string in a circle? Do you remember that the faster you swung the object, the harder it was to hold?

The force that caused it to move in a circle, rather than a straight line, was centripetal force, exerted by the string. The force pulling against your hand was centrifugal force, which was increasing as you spun it faster.

When you depress the brake pedal, your brakes squeeze the wheels until they stop spinning. This produces friction between the wheels and the brakes, converting the kinetic energy in your spinning wheels into heat.

The friction between your wheels and the brakes, along with the friction between your tires and the road, causes your car to come to a stop. However, if you are traveling too fast when you apply the brakes, so much heat will be produced that your brakes may overheat and become unable to absorb enough kinetic energy to stop your car.

Turning the steering wheel excessively or abruptly may cause weight to shift to the side of the vehicle, making it spin to the left or right around its center of gravity

This is known as Yaw.Problems involving yaw are more likely to occur when the rear tires lose traction.

The amount of friction between two objects is affected by the nature of their surfaces. The smoother the surface of an object is, the less friction it produces.

Tires are made of rubber and rubber-like synthetic materials because they produce a great deal of friction with the road. Asphalt roads are also designed to produce a high amount of friction. However, when a road is wet or covered with loose material like dirt, less friction will be produced.

The friction between your tires and the surface of the road is specifically known as Traction. This force is created by the weight of your car pushing the tires down onto the road surface.

Traction allows you to accelerate, brake, and change directions.The faster you drive, the less traction your wheels have with the road. With decreased traction, the possibility of skidding increases.

By wisely using your knowledge of how centripetal and centrifugal forces affect your driving, you can become a better and safer driver.

Use your brake to slow down before you enter a curve. Avoid braking on a curve. Braking when you are in a curve may cause your vehicle to skid, especially if you brake hard while turning sharply. Shift to a low gear before entering a curve. When rounding a curve, bicyclists and motorcyclists should lean towards the inside of the curve to keep their balance.

The principle underlying friction is Resistance. Resistance is any tendency to inhibit motion. The more resistance you need to overcome due to friction, inertia, or other natural forces, the more energy you will need to use to attain the same speed.

While resistance tends to inhibit motion, it is also necessary to overcome inertia to initiate motion. A car is propelled forward by the force of its tires pushing against the resistance created by the road surface: the car begins moving only after the force exceeds the inertia.

Winter weather is especially likely to decrease the traction

between your wheels and the road surface. For instance, stopping on wet asphalt can take up to 25% longer than in dry conditions.

Active Steering Control Systems, also known as Electronic Stability Programs (ESP)

minimize the chance of oversteering and understeering by comparing a driver's steering motions with where the car is actually going. If the system senses a disparity between the two, it will selectively apply the vehicle's brakes to help the driver retain control of the car. For instance, ESP will activate the outside front brake to reduce oversteering, and apply the inside rear brake to reduce understeering.

Vehicle Balance

refers to the distribution of a vehicle's weight across its four tires as they meet the ground. A vehicle in good working order that is parked on level ground is at its ideal balance.Good vehicle balance also depends on having wheels with optimal tire pressure and a suspension system that is working properly. The suspension system is your vehicle's system of springs, shock absorbers, and linkages connecting the vehicle to its wheels.

Loss of traction in your car's rear tires

results in oversteering

Loss of traction in your car's front tires

results in understeering.

Centrifugal force

(which means center-fleeing force) pushes an object away from a center of a curve. Centrifugal force increases with acceleration.

A vehicle can lose its balance or traction if you stop abruptly in a panic, press down too hard on the brakes, or speed excessively, especially on hills and curves. If you realize you are moving too quickly as you approach a curve, you should:

Brake before you get to the curve, then ease off of the brake as you enter the curve. Press the brake gently if you continue to move too quickly through the curve. Accelerate gently at the midpoint of the curve to stabilize your vehicle. Be especially cautious if the shoulder beside the curve is unpaved. If you end up driving onto the shoulder, the change in traction will make it more difficult to regain control of your car.

In addition to traction, another force that affects your car's tires is Rolling Resistance. As they roll, your tires will change shape due to the force of your car's weight on them. This causes them to experience repeated cycles of deformation(being flexed out of shape) and recovery(returning to the proper shape).

During this process, some of the energy produced by the engine and transferred to the wheels is converted to heat and radiated away or dissipated. The more the tire deforms, the more it must recover, and therefore the more resistance is generated.

Cars that have a higher center of gravity are more likely to flip or roll over in a collision.

For instance, because of their size and distance from the ground, SUVs have high centers of gravity and are particularly likely to roll over.

Pay attention to your kinesthetic sense—your sense of your body's position and motion—to determine whether your vehicle is not balanced properly. When driving a car, you can feel the forces that its motion exerts on you.

For instance, you will feel pushed backwards when your car accelerates sharply. Because of your kinesthetic sense, you don't need the pressure of the seat behind you to have the knowledge that your car is speeding up.

Newton's Second Law: F = ma

Force (F) is equal to mass (m) multiplied by acceleration (a). This principle indicates that the force an object possesses is influenced both by its weight and its speed. As a result, driving faster and driving a heavier vehicle will both increase the severity of an impact. If two cars collide head on, the force of impact will involve the mass of both cars and the rate at which they approached each other.

When driving downhill, maintain a safe speed by shifting to a lower gear.

If driving with an automatic transmission, shift out of the automatic Drive gear to the fixed First or Second gear setting, if available.

Most of the time, weight will be transferred in multiple directions at the same time. By understanding how these forces interact, you will be better able to maneuver your car safely.

If you apply your brakes while traveling through a curve at a high speed, the resulting weight transfer to the front wheel opposite the direction of the turn may produce severe traction loss. You may skid badly. By applying your brakes close to the point where they will lock up before you begin a turn or enter a curve, the weight transfer to your front wheels will give you better traction when you begin the maneuver.

Remember the effects of the centripetal and centrifugal forces whenever you turn or drive through a curve.

If you enter a curve too fast while driving on the inside of a curve, centrifugal force may pull your car into the path of oncoming traffic. If you enter a curve too fast while driving on the outside of the curve, centrifugal force may pull your car off the road. This can be especially dangerous if you're driving on a mountain road! If the road is wet or icy, there will be less friction between your tires and the road, so there will be less centripetal force, and this means you will have to drive especially cautiously as you enter a curve.

The force of any collision is dependent not only on the energy of your car, but also on the energy of the car or object you collide with. Remember, Newton's Third Law states that for every action, there is an equal and opposite reaction. Consider:

If you hit a stationary punching bag, the force of your fist will be much greater than the force of the bag and the bag will swing away. After the bag has swung away, the chain attached to the bag will pull it back in the direction of your fist. If you hit it again as it swings towards you, it will have a greater amount of force due to its greater kinetic energy. If you hit a brick wall, the force of the stationary wall will be much greater than the force of your fist and the energy will be directed back into your fist, injuring your hand.

If you drive with worn-out tires, there will be less traction between your tires and the road, and it will be difficult to drive smoothly, stop quickly, and pull out of a curve without losing control of the vehicle.

If your tires are overinflated, they will have rounder surfaces, decreasing your traction with the road. If your tires are underinflated, they will deform more as you drive and increase your traction with the road, and will provide you a less stable platform for turns. When tires are overheated, they will expand more and offer less traction. Excess speed or hot roads can increase the temperature of your tires.

Kinetic Energy is the energy an object possesses because of its motion. If the brakes of a car parked on top of a hill fail, the car's potential energy will be converted to kinetic energy.

Kinetic energy increases with speed and determines how easily something can be stopped.When you stop, any kinetic energy your car has acquired must be absorbed by your brakes or other sources of friction. If you stop suddenly, your car's kinetic energy won't be absorbed gradually by the brakes or by friction. Instead, that energy will be absorbed by your body, your vehicle's body, and any objects you collide with.

When responding to front wheel traction loss:

Look in the direction you want to go. Gently turn your steering wheel in the direction you want to go. Until the car regains traction, make only small steering adjustments. Ease your foot from the brake or accelerator pedal so that your car's weight will be more balanced. Jab the brake to shift some weight forward towards the front wheels. Once you have regained some traction, your car will become more responsive to steering input. When your treads grab the road, your car will lurch slightly and then start moving in the desired direction.

At the same time, your car naturally seeks to continue moving in a straight line because of inertia. This causes it to pull away from a turn, creating centrifugal force.

The faster you accelerate into a curve, the more your car is pulled in the original direction by the force of inertia. As the centrifugal force acting on your car increases, the arc of your turn becomes wider.

Make sure your tires have enough traction. The primary factors affecting the amount of traction between your tires and the road are:

The weight of your vehicle Whether your tires are properly inflated The material of the road The condition of the road Remember, traction decreases as the speed of your tires increases. At a certain point, your wheels can spin so fast that they can overcome the force of friction, causing your car to skid.

As a vehicle accelerates, weight is transferred towards its rear.

This is known as Backward Pitch. Accelerating more rapidly causes more weight to be transferred: the hood will rise noticeably and the rear of the vehicle will drop.No matter how you accelerate, you will experience some backward pitch. However, by applying light or gradual pressure to the accelerator pedal, weight will be transferred to the rear more slowly, minimizing the effect on your car's balance.

When the brakes are applied, weight is transferred to the front of a vehicle. If braking is hard, the hood will drop noticeably and the rear deck of the vehicle will rise.

This is known as Forward Pitch.If you apply your brakes gradually while traveling in a straight line, weight will be distributed more evenly across all four wheels. However, if you apply your brakes abruptly, you may completely lose traction and directional control. Combined with the weight transfer, this situation can be extremely dangerous.

Road elevation can affect a vehicle's side-to-side balance. When going uphill, try to keep your car parallel with the slope of the hill so that its weight will be more equally distributed across all four tires.

When driving up a steep hill, maintain a steady speed by increasing pressure on the accelerator. This will keep the front of the vehicle from rising. Apply pressure to the brakes or shift to a lower gear when driving downhill so that your car won't move too fast.

The principle of Inertia—the tendency of a body in motion to stay in motion and a body at rest to stay at rest—applies to your vehicle and everything inside it.

When stopped, your car will not start unless you engage the engine or it is pushed by another car. When moving, your car will keep moving until another force slows it down or stops it. A driver can apply this force by depressing the brake, or this force can come from an external source such as the surface of the road, a fixed object (such as a telephone pole), or another vehicle.

The force of traction is explained by Newton's Third Law:

your car's wheels must be able to push against the surface of the ground to begin moving, and the ground must push against your car's tires enough to absorb their kinetic energy to stop your car. Without sufficient traction, your wheels will slip and you won't be able to start, stop, or turn.