Chapter 30 ARL

Advanced Brake Systems

Electronic Brake Control You might think, "If some brake force is good, then more would be better." But this is not the case. Applying too much brake force can cause the tire to lose traction and skid. If this happens, the driver can lose control of the vehicle. This problem led to the design of electronic brake control (EBC) systems. The first versions of EBC systems were the anti-lock brake systems (ABS). ABS have helped to reduce the number of vehicle accidents each year. They use a computer to monitor each wheel's speed and either hold, decrease, or apply the hydraulic pressure to each wheel to prevent wheel lock-up and maintain the maximum amount of braking power just short of brake lock-up. Additional safety demands led to the development of traction control systems (TCS) and electronic stability control (ESC). TCS systems help to prevent tires from slipping during acceleration by reducing engine torque and, if necessary, applying brake pressure to the slipping wheels. ESC adds additional functionality to ABS and TCS to help prevent the tires from losing traction when the vehicle is being steered aggressively or evasive maneuvers are being undertaken. In both TCS and ESC, the control unit can independently apply individual brake units even though the driver is not stepping down on the brake pedal. Brake Assist and Brake-by-Wire Systems Electronic brake control systems have been further enhanced with additional programmed features such as brake assist (BA). BA gives greater control of the braking system to the computer, which can react more quickly and more deliberately than a driver, especially in a panic situation. An example of BA is the brake-by-wire system. A full brake-by-wire system does away with the hydraulic portion of the brake system and replaces it with sensors, wires, an electronic control unit, and electrically actuated motors to apply individual brake units at each wheel. The driver applies foot pressure to a brake pedal emulator. This tells the computer how firmly the driver intends to brake. The control unit then sends control signals to the appropriate brake actuators, which generate the commanded clamping force and slow the vehicle. All of this is being monitored by sensors reporting data to the control unit, so the desired braking occurs. Giving greater control of the braking system to the computer increases driving safety. For example, it takes a certain amount of time and stopping distance for the driver to lift his or her foot from the accelerator pedal, step on the brake pedal, and apply the wheel brake units. In a brake-by-wire system, that time and distance can be reduced. The computer can determine that the driver is quickly releasing the accelerator, which indicates a potential panic stop. As the pedal is being released, the control system immediately applies the brakes lightly, which dries any moisture from the braking surfaces and takes up any clearance in the brake system. This prepares the brakes to be fully applied by the control system if the driver steps on the brake pedal or if the computer detects that a collision is about to happen. Regenerative Brake Systems With the pressure to improve fuel economy, some manufacturers have equipped their hybrid vehicles with regenerative braking. Regenerative braking takes brake-by-wire technology to the next level. Instead of applying friction brakes and losing energy as heat, the brake-by-wire system uses the electric motor as a generator, which slows the vehicle by converting the vehicle's kinetic energy into electrical energy. The amount of stopping power is controlled by how much electricity is being generated. The more stopping power needed, the more electrical output is demanded of the generator (up to its maximum rated output) by the control system. The electricity is stored in the vehicle's high-voltage battery and can then be used later by the electric motor to drive the vehicle. This regeneration process makes the vehicle more fuel efficient, especially in stop-and-go traffic.

Heat Transfer

Heat transfers from a hot area to a cool area. Since there is a lot of kinetic energy converted to heat during the braking process, the brakes must be able to dissipate that heat to the atmosphere effectively. Heat transfer is critical to this process. Heat must continually be transferred away from the friction materials so that the brakes can perform their job of transforming the kinetic energy into heat energy. Ultimately, most of the heat generated by the braking process radiates into the atmosphere. How it radiates into the atmosphere depends on the type of braking system. In drum brakes, the heat is created inside of the drum and transfers through the drum to the outside surface where it radiates into the atmosphere. In disc brakes, the heat is created on the outer surfaces of the rotors, which are in contact with the atmosphere. Disc brakes also may have internal ventilation to help dissipate the heat transferred from the outer surface even faster.

Acceleration and Deceleration

Newton's first law of motion states that "an object will stay at rest or uniform speed unless it is acted upon by an outside force." Acceleration refers to an increase in an object's speed. In an automobile, acceleration, or an increase in kinetic energy, is caused by the power from the engine. When the driver steps down on the throttle pedal, the engine's power output is increased and the vehicle accelerates. This acceleration requires a certain amount of energy. The heavier the vehicle, the more energy required to accelerate it to a given speed. A lighter vehicle requires less energy to accelerate; this is why race cars are stripped of all unnecessary weight. AppliedScience AS-51: Acceleration/Deceleration: The technician can demonstrate an understanding of a vehicle's acceleration and deceleration as a function of vehicle weight and power. Kinetic energy is the energy of an object in motion. All moving objects have kinetic energy. Heavier objects have more kinetic energy than lighter objects moving at the same speed. If the weight doubles, the kinetic energy doubles. Energy is needed to start a vehicle. Heat energy is generated in the engine via chemical energy (fuel); it is then converted via mechanical energy to kinetic energy, putting the vehicle in motion. Kinetic energy is converted to heat energy once again through the operation of the brakes. This heat energy is then dissipated in the surrounding air through the brake system, bringing the vehicle to rest. Newton's first law of motion states that the greater the weight, the more energy is needed to accelerate and maintain speed. For example, it is easier for three people to push a two-door hatchback than an SUV. Also, the more the vehicle weighs, the more energy it takes to decelerate. Deceleration refers to a decrease in an object's speed. Remember that an outside force is needed for the speed of an object to change. So we need an outside force to act upon the vehicle to cause it to decelerate. That force comes from the mass of the Earth. If you thought it came from the brakes, you would only be partially correct. Imagine traveling at a high speed in a four-wheel drive vehicle and hitting a bit of a jump. Stepping on the brakes in midair to slow the vehicle wouldn't do you much good, would it? So the brakes only function when they connect the vehicle to the ground or roadway. In fact, that is what they do; they connect the vehicle to the ground through the rolling wheel and tire assembly. In doing so, they apply a varying amount of force from the ground to the vehicle, thereby causing the vehicle to decelerate. The force of the brakes absorbs the kinetic energy of the vehicle. The heavier the vehicle and the faster it is going, the more kinetic energy must be dissipated and the harder the brakes must work.

BRAKE REPAIR LEGAL STANDARDS AND TECHNICIAN LIABILITY

Brake repair is right up with steering and suspension repair on the liability scale. Improperly repaired brakes can function reasonably well under normal driving situations but can fail during a panic situation when they are needed the most. The likelihood of accidents, injury, or death goes up drastically in those situations. Shops and technicians have been successfully sued for improper brake repairs resulting in large cash settlements. Technicians also risk being found criminally negligent if they are determined to have acted maliciously. Always follow the manufacturer's procedures when servicing brake systems. Research service information, precautions, and technical service bulletins. Never take shortcuts, which could cause the vehicle to be unsafe. Remember, safety first! SAFETY Asbestos is a naturally occurring mineral mined from the earth. Asbestos is a long, very thin fibrous crystal. When asbestos is disturbed, small needle-like fibers can break off and remain airborne, where they are inhaled by people. Since these fibers are so small, they embed themselves deep within lung tissue, causing scarring. Repeated exposure can lead to asbestosis and lung cancer. While asbestos has been removed from most brake and clutch materials, it is still present in some replacement and old components. Therefore, you must treat all brake and clutch dust as if it contains asbestos. This is accomplished by using an aqueous brake wash station, a HEPA brake dust vacuum system, or, in some states, an aerosol can of brake cleaning solution to carefully wash down the brake components

Levers and Mechanical Advantage

Brake systems use levers and mechanical advantage to apply service and parking brakes. A simple example of a lever is a bar. The point around which a lever rotates and that supports the lever and the load is called the fulcrum. A lever allows the user to lift a large load over a small distance at one end by applying a small force over a greater distance from the other end. The effort distance is from the fulcrum to the point effort is applied. The load distance is from the fulcrum to the point the load is applied.The effort required to move a load depends on the relative distance of the load and the effort from the fulcrum. The ratio of load and effort is called mechanical advantage. If the effort distance from the fulcrum is greater than the load distance, then the effort required will be less than the load being moved. If the load distance is greater than the effort distance, then the effort required is greater than the load being moved. This is known as a negative mechanical advantage or mechanical disadvantage. FIGURE 30-18 Lever of the third order. Using the right kind of lever in the right way allows a user to move larger loads with less effort. There are three basic types of levers: Lever of the first order: The fulcrum is in the middle, between the load and the effort FIGURE 30-15. Examples are a pry bar or a seesaw. The force applied in this situation is in the opposite direction of the load. Lever of the second order: The load is in the middle, between the effort and the fulcrum FIGURE 30-16. An example is a wheelbarrow. The force applied in this situation is in the direction of the load. Brake pedals are usually of the second order. They pivot at the top end (fulcrum). The foot pressure (effort) is applied to the bottom end. And the master cylinder (load) is applied between the two. Mechanical advantage is engineered into the brake pedal to provide the proper brake pedal application and feel FIGURE 30-17. Lever of the third order: The effort is in the middle, between the load and the fulcrum FIGURE 30-18. An example is an oar when paddling a canoe, where the hand holding the top of the oar is the fulcrum, the other hand holding the middle of the oar is providing the effort, and the water is the load. The force in this situation is in the direction of the load.

Friction and Friction Brakes

Brakes transform kinetic energy to another form of energy. Standard brakes do this through the principle of friction. Friction is the resistance created by surfaces in contact. Static friction is resistance between nonmoving surfaces and is present in parking brakes. Kinetic friction is resistance between moving surfaces and is present in standard brakes. Just as rubbing sandpaper over a block of wood produces heat, operating the brakes causes the moving friction surfaces to come into contact with each other and generate heat. This transformation of energy converts kinetic energy into heat energy and slows the vehicle. If you have seen an old go-kart, you may have noticed the scrub brake. The metal pad scrubbing against the tire causes friction, which slows the go-kart—while also wearing down the tires. As discussed previously, modern vehicles use a more sophisticated braking system with separate braking components that operate more efficiently. The amount of friction between two moving surfaces in contact with each other is expressed as a ratio and is called the coefficient of friction. It can be found by comparing the amount of force pushing the two surfaces together to the amount of resistive force generated between the two surfaces sliding against each other. For example, a stationary steel surface pushed against a moving steel surface with 100 lb (45.36 kg) of force might generate 20 lb (9.07 kg) of resistive force. This is expressed as 20/100 (9.07/45.36), which equals a coefficient of friction of 0.20. A stationary block of rubber that is pushed against a moving steel surface with 100 lb of force might generate 125 lb (56.7 kg) of friction. This would be 125/100 (56.7/45.36), which equals a coefficient of friction of 1.25. TECHNICIAN TIP A higher coefficient of friction usually results in a faster wearing of the softer material, such as rubber. This is one reason why the brake lining is designed to be made of softer materials than the drum or rotor, which leads to the wearing out of the brake lining instead of the drum or rotor. AppliedScience AS-90: Friction: The technician can demonstrate an understanding of friction and its effects on linear and rotational motion. When adjusting drum brakes, the common method is to adjust the brake and turn the wheel at the same time in order to feel how hard it is to turn the wheel while adjusting the brake. As the brake becomes tighter, the friction between the brake drum and the brake shoe increases; therefore the rotational motion requires more torque or force to produce the same speed of movement. Linear friction is demonstrated when a heavy object is pulled across a flat surface. The more surface area that is in contact with the object, the harder it is to pull. The larger the surface area that the object is covering, then the greater the force required to move it. For example, try to pull a tool box across a bench. Now lift one end of the toolbox and pull. It is far easier to pull the toolbox with one end lifted because the lifted tool box is in contact with less surface area, reducing the force required to move the box. AppliedScience AS-91: Friction: The technician can explain the role that friction plays in acceleration and deceleration. Friction is very important to acceleration and deceleration. A vehicle's tires must be able to keep friction between the tire and the ground in order to propel the car forward. If the tires are not in contact with the road, they will have nothing to push against. No friction is present and the car will not move forward. Friction is also very important in deceleration, as the tire again has to maintain friction between the road surface and tire. The braking force on the vehicle will also use friction in order to slow or decelerate the vehicle. As the brake pads press against the brake disc, friction is created between the two surfaces. This friction creates heat and slows the vehicle.

THE HISTORY OF BRAKES

Early automobiles evolved from horse-drawn buggies and used a similar scrub braking system. Scrub brakes are a simple mechanical system that uses leverage to force a friction block against one or more wheels. In a buggy, for example, the friction between the two surfaces transformed the energy of the moving buggy into heat energy. As heat was created in the friction materials, the buggy slowed down. The scrub braking system was used for more than 2000 years with virtually no change. It worked reasonably well on dry wheel surfaces made of wood or steel but became quickly outdated once rubber tires were developed around 1900, since the scrubbing action on the softer tires significantly decreased tire lifeFaced with the need to replace the scrub braking system with a system that did not apply friction materials directly to the new rubber tires, designers had to consider other options. One option was the band brake. It used a metal band lined with friction material that was operated mechanically to clamp around the outside of a small-diameter wheel or was drum-mounted to the axle or wheel. This system worked well in the forward direction, but the band would try to unwind in the reverse direction; the system was therefore impractical and was abandoned after just a few short years. The next major development was the drum brake, which is similar to the drum brakes that are used today. The drum brake consisted of two brake shoes that would push against the inside of the brake drum. Early drum brake systems were mechanically operated by rods, links, and levers FIGURE 30-1. This worked fine for applying a single brake unit, but as vehicle operating speeds increased, greater braking demands required brake units to be mounted to each wheel. With this mechanically operated system of rods, links, and levers, it was difficult to maintain equal braking forces at each wheel. The old drum braking systems caused the vehicle to veer dangerously to one side when braking. This system also required frequent adjustment of the brakes. Over time, the mechanical drum brake system gave way to the modern hydraulic drum brake system due to its ability to automatically equalize braking forces at each wheel. Disc brakes were originally developed in the early 1900s but didn't find common use until the 1960s. Because the effectiveness of friction brakes depends on the braking components' ability to dissipate heat quickly into the atmosphere, drum brakes—with their friction materials on the inside—were at a disadvantage. This led to the greater use of disc brakes on most vehicles FIGURE 30-2. Disc brakes force brake pads against the outside of the brake rotor and create heat where atmospheric air can quickly remove the heat at its source, making them more efficient under prolonged use.

Brake Fade

In automobiles, brake fade is the reduction in stopping power caused by a change in the brake system. Brake fade can be caused by three factors. The first and most common is heat fade. Heat fade is caused by the buildup of heat in the braking surfaces, which get so hot they cannot create any additional heat, leading to a loss of friction. Remember, the brakes must transform kinetic energy into heat energy to decelerate the vehicle. If heat energy cannot be generated, then the kinetic energy cannot be reduced and the vehicle will not decelerate. Heat transfer is used to move heat away from the friction surfaces and allow them to continue generating heat. Once the temperature of the friction materials become so hot that they cannot generate any additional heat, the coefficient of friction drops and the brakes cannot generate stopping power until some of the heat dissipates. A driver will experience heat fade after using the brakes too much, such as during high-performance driving or when going down a long, steep hill, particularly when towing. The brake pedal will be hard, but the braking effect "fades" away and the vehicle's rate of deceleration decreases. This is a dangerous condition and is why many long hills on freeways have truck escape ramps made of sand or some other soft material to slow a vehicle by absorbing the truck's kinetic energy in the soft material. The second type of brake fade is called water fade and is caused by water-soaked brake linings. The water acts like a lubricant and lessens the coefficient of friction between the braking surfaces. This leads to a hard brake pedal but very little braking power. Once the water is removed from the friction surfaces through evaporation, the normal coefficient of friction will be restored. The third kind of brake fade is called hydraulic fade and is caused by the brake fluid becoming so hot that it boils. Once it boils, it is no longer only a liquid, converting in part to a vapor, which can be compressed. The brake fluid can no longer transfer force effectively to the wheel brake units and apply them firmly enough to create friction. Since the boiling fluid can be compressed, hydraulic fade can be recognized by the brake pedal becoming soft and having increased pedal travel during heavy brake usage.

BRAKE FUNDAMENTALS

Several factors can influence vehicle braking. An effective braking system takes all of the following factors into account: Road surface: Generally asphalt and concrete road surfaces allow for good braking while gravel surfaces or dirt roads do not. Road conditions: Roads that are wet, icy, or covered with loose gravel reduce the tire's traction and result in longer stopping distances. Extremely hot temperatures on asphalt roads can soften the asphalt, making it slippery. Weight of the vehicle: Heavier vehicles require more braking force to stop than lighter vehicles and therefore usually have larger wheel brake units. Also, loading down a vehicle increases its stopping distance due to the vehicle's extra mass. Load on the wheel during stopping: Heavier loads increase the downward force on the wheels, thereby increasing tire traction FIGURE 30-3. Height of the vehicle: Stopping power is exerted at the point where the tire and the road connect. The centerline of the vehicle's weight is above this tire-to-road contact point. The taller the vehicle, the greater the leverage on the contact point. This increases the load on some tires, while decreasing the load on other tires. Thus, controlling the vehicle in a panic situation becomes much more difficult. How the vehicle is being driven: Aggressive driving causes the tires to become hot and possibly overheated, thus reducing the tire's ability to obtain maximum traction. Also, increased speed and aggressive handling force the brakes to work under extreme conditions. The tires on the vehicle: A tire's composition, tread style, tread condition, and inflation pressure all affect its traction FIGURE 30-4. Manufacturers design tires with different qualities based on vehicle need. Tires are rated for their traction ability. Using the wrong tire will affect the vehicle's stopping power. For example, a tire with tread designed to channel water away from the tire-to-road contact point will have greater traction when the road surface is wet than the tires used on drag race cars, which have a slick tread.

Adjustable Brake Pedal System

Some vehicles come equipped with adjustable pedal assemblies. Such assemblies allow the driver to raise or lower the brake and throttle pedal assembly for personal comfort. These are usually adjusted by electrically driven motors that are operated by a switch on the steering column or dash FIGURE 30-19.

INTRODUCTION

The brake system is one of the most critical systems on a vehicle. It allows the driver to slow or stop the vehicle as needed. In ideal situations, the driver will have enough time to anticipate the need to slow down well in advance of an event, allowing the vehicle to slow down gradually. However, many situations require the quick use of a very efficient braking system to avoid an accident. In this chapter, we will explore the history, theory, and operation of modern braking systems.

Energy Transformation

The law of conservation of energy states that energy cannot be created or destroyed. This means that the energy used to cause a vehicle to accelerate and decelerate must be transformed from one form of energy to another. Let's follow the cycle of energy transformation in a typical vehicle.Gasoline or diesel fuels are potential energy in chemical form. A portion of the fuel's chemical energy is transformed within the engine, first into heat energy and then into mechanical energy. Engines are not very efficient, only transforming about 25% to 35% of the chemical energy into mechanical energy. The rest of the chemical energy is wasted as heat energy, mostly through the exhaust and cooling systems. The mechanical energy is used to accelerate the vehicle, thus converting the mechanical energy to kinetic energy. Once the vehicle is up to speed, the engine only needs to transform enough chemical energy into kinetic energy to overcome wind resistance, climb hills, and power the vehicle's accessories. This is why most vehicles get better fuel economy while operating at steady speeds than in stop-and-go traffic—it takes a lot more energy to accelerate a vehicle than it does to maintain a particular speed. Does deceleration require an energy transformation? Yes, it does. The kinetic energy has to be removed for the vehicle to decelerate. In other words, the kinetic energy must be transformed into another form of energy for the vehicle to slow down. In a standard vehicle, the braking system transforms the kinetic energy into heat energy FIGURE 30-12. In essence, it takes the same amount of energy to slow a vehicle as it does to accelerate it. For safety's sake, we expect a vehicle to stop from a given speed faster than the time it took to accelerate to that speed. For this reason, the braking system can transform energy faster than the engine.

Brake Systems

There are two brake systems on all vehicles—a service brake and a parking brake. The service brake is used for slowing or stopping the vehicle when it is in motion and is operated by a foot pedal FIGURE 30-5. Service brakes consist of drum and/or disc brakes. Some have disc brakes on the front wheels and drum brakes on the rear wheels, while others have disc brakes on all four wheels. The parking brake is used for holding the vehicle in place when it is stationary. The parking brake is usually operated by hand, but some vehicles use a foot-activated pedal FIGURE 30-6. Modern braking systems are hydraulically operated and have two main sections: the brake assemblies at the wheels and the hydraulic system that applies them. The driver pushes the brake pedal, which applies mechanical force to the pistons in the master cylinder. The pistons apply hydraulic pressure to the fluid in the cylinders. The lines transfer the pressure—which is applied equally in all directions within the confines of the brake lines—to the hydraulic cylinders. The hydraulic cylinders at the wheel assemblies apply the brakes FIGURE 30-7. Force is transmitted hydraulically through the fluid. For cylinders of the same size, the force transmitted from one is the same value as the force applied to the other. By using cylinders of different sizes, forces can be increased or reduced, allowing designers to obtain the desired braking force for each wheel FIGURE 30-8. The cylinders force friction linings into contact with the braking surfaces. The resulting friction between the surfaces generates heat energy and slows the vehicle. In drum brakes, the wheel cylinders force brake linings against the inside of the brake drum FIGURE 30-9. In disc brakes, pads are forced against the outside of a brake disc FIGURE 30-10. In both systems, heat spreads into other parts and the atmosphere, so brake linings and drums, pads and discs, and brake fluid must withstand high temperatures and high pressures. On modern vehicles, the basic brake system has some refinements such as a power booster and EBC systems. These help the driver apply the brakes, prevent skidding, and maintain directional control of the vehicle under various driving situations FIGURE 30-11.

Principles of Engine Braking

When a vehicle is in gear, the crankshaft of the engine and the wheels are mechanically connected. When turning force is applied to the crankshaft by the engine, the transmission applies that force to the wheels. Alternatively, if force is applied to the wheels, the transmission applies that force to the engine through the crankshaft. This is the principle behind push-starting a vehicle equipped with a manual transmission. Force is applied to the wheels by pushing the vehicle; when the vehicle has some momentum, engaging a gear turns over the engine, enabling it to start without the assistance of a starter motor. Engine braking uses this same principle. If you take your foot off the accelerator, so that the engine ceases to apply force to the wheels, the engine begins to act as a brake on the vehicle. As the engine slows down, the momentum of the wheels will keep it turning over. The compression stroke of the engine will soak up some of this kinetic energy, slowing the vehicle. Engaging a lower gear will slow the vehicle more quickly, as the engine will be turned over more rapidly by the movement of the wheels. Slowing a vehicle while traveling down a steep or very long decline using normal wheel brakes alone can lead to heat buildup and potentially dangerous brake fade. It is good practice to slow the vehicle initially with the brakes, then to shift the transmission into lower gears and let the inertia of the engine assist in slowing the vehicle, and prevent it from accelerating again. This approach is safer because engine braking can be sustained for longer periods of time without reducing braking effectiveness. It also reduces the wear and tear on the brake assemblies.

Rotational Force

When brakes are operated on a moving vehicle, a rotational force is generated. As the wheel rotates, the friction between the brake components tends to twist the brake support in the direction of wheel rotation FIGURE 30-13. Since the brake support is ultimately connected to the body of the vehicle, the body too tends to rotate in the same direction. A good example of rotational force is when a motorcycle rider applies the front brake hard enough that the rear wheel is lifted completely off the ground. Rotational forces are usually controlled by the suspension components, but they can become worn and allow movement, which can be felt as a clunk or pop during brake application. Another result of rotational force is weight transfer. The rotational force tends to push the nose of the vehicle down and lift the rear of the vehicle, transferring weight to the front wheels. Rotational force and weight transfer also happen because the centerline of the vehicle is higher than the centerline of the axles; thus, the center of gravity tends to move forward when the brakes are applied firmly FIGURE 30-14.Weight transfer causes the front wheels to have increased traction, allowing them to bear more of the stopping load, and causes the rear wheels to have less traction, reducing the amount of load they can bear. Engineers take this into account when designing the brakes; otherwise the front wheels will not get enough stopping power and the rear will have too much, resulting in rear wheel lockup and loss of control of the vehicle. Lock-up is avoided by engineering the system with the proper-sized master and wheel cylinders and valving that modifies the hydraulic pressure to the rear wheels under hard braking. This is covered in greater detail in the Hydraulic Components section in the Hydraulics and Power Brakes chapter. CARING FOR THE CUSTOMER Some owners raise their vehicles for better off-road clearance by installing a lift kit and/or large-diameter tires. Doing so raises the vehicle's center of gravity and increases the amount of weight transfer the vehicle experiences, making it more prone to rear-wheel lock-up and vehicle rollovers. It is important to only use lift kits engineered for the particular vehicle. After installing such a kit, inform the driver of the effect that a higher center of gravity will have on vehicle operation.

Kinetic Energy

is the energy of an object in motion. All moving objects have kinetic energy. Heavier objects have more kinetic energy than lighter objects moving at the same speed. If the weight doubles, the kinetic energy doubles. Faster-moving objects have more kinetic energy than slower-moving objects of the same weight. Kinetic energy increases by the square of the speed. This means that if we double the speed of an object, the kinetic energy will increase by four times. If we triple the speed, the kinetic energy will increase by nine times. Thus, the heavier and faster an object is, the greater its kinetic energy. During braking, all of the kinetic energy in the moving vehicle must be converted to another form of energy (in most cases heat) for the vehicle to stop moving; this is the function of the braking system.