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#10795. What does the term in Geography Desertification mean?

#10796. What does the term in Geography Desire path mean?

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#2597. What does the medical term Hyperplasia mean?

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#6376.

2523) Hematite

Gist

Hematite is a common iron oxide mineral and the world's most important iron ore, containing roughly 70% iron. It is recognized by its brilliant metallic gray to dull red color and characteristic reddish-brown streak, which is used for pigments and polishing. It is abundant on Earth and causes the red coloration on Mars.

Hematite occurs in a variety of igneous and metamorphic rocks, but is most abundant in sedimentary settings. In sedimentary rocks, hematite can either have formed from have originally formed directly from direct precipitation out of marine waters, or as a concentration and enrichment deposit formed from groundwater.

Summary

Hematite is a heavy and relatively hard oxide mineral, ferric oxide (Fe2O3), that constitutes the most important iron ore because of its high iron content (70 percent) and its abundance. Its name is derived from the Greek word for “blood,” in allusion to its red colour. Many of the various forms of hematite have separate names. The steel-gray crystals and coarse-grained varieties have a brilliant metallic lustre and are known as specular iron ore; thin scaly types are called micaceous hematite. Much hematite occurs in a soft, fine-grained, earthy form called red ochre or ruddle. Intermediate between these types are compact varieties, often with a reniform surface (kidney ore) or a fibrous structure (pencil ore). Red ochre is used as a paint pigment; a purified form, rouge, is used to polish plate glass.

The most important deposits of hematite are sedimentary in origin. The world’s largest production (nearly 75 million tons of hematite annually) comes from a sedimentary deposit in the Lake Superior district in North America. Other important deposits include those at Minas Gerais, Brazil (where the hematite occurs in metamorphosed sediments); Cerro Bolívar, Venezuela; and Labrador and Quebec, Canada. Hematite is found as an accessory mineral in many igneous rocks; commonly as a weathering product of siderite, magnetite, and other iron minerals; and almost universally as a pigmenting agent of sedimentary and other rocks. For detailed physical properties, see oxide mineral.

Details

Hematite is one of the most abundant minerals on Earth's surface and in the shallow crust. It is an iron oxide with a chemical composition of Fe2O3. It is a common rock-forming mineral found in sedimentary, metamorphic, and igneous rocks at locations throughout the world.

Hematite is the most important ore of iron. Although it was once mined at thousands of locations around the world, today almost all of the production comes from a few dozen large deposits where significant equipment investments allow companies to efficiently mine and process the ore. Most ore is now produced in China, Australia, Brazil, India, Russia, Ukraine, South Africa, Canada, Venezuela, and the United States.

Hematite has a wide variety of other uses, but their economic significance is very small compared to the importance of iron ore. The mineral is used to produce pigments, preparations for heavy media separation, radiation shielding, ballast, and many other products.

Physical Properties of Hematite

Hematite has an extremely variable appearance. Its luster can range from earthy to submetallic to metallic. Its color ranges include red to brown and black to gray to silver. It occurs in many forms that include micaceous, massive, crystalline, botryoidal, fibrous, oolitic, and others.

Even though hematite has a highly variable appearance, it always produces a reddish streak. Students in introductory geology courses are usually surprised to see a silver-colored mineral produce a reddish streak. They quickly learn that the reddish streak is the most important clue for identifying hematite.

Hematite is not magnetic and should not respond to a common magnet. However, many specimens of hematite contain enough magnetite that they are attracted to a common magnet. This can lead to an incorrect assumption that the specimen is magnetite or the weakly magnetic pyrrhotite. The investigator must check other properties to make a proper identification.

If the investigator checks the streak, a reddish streak will rule out identification as magnetite or pyrrhotite. Instead, if the specimen is magnetic and has a reddish streak, it is most likely a combination of hematite and magnetite.

Composition of Hematite

Pure hematite has a composition of about 70% iron and 30% oxygen by weight. Like most natural materials, it is rarely found with that pure composition. This is particularly true of the sedimentary deposits where hematite forms by inorganic or biological precipitation in a body of water.

Minor clastic sedimentation can add clay minerals to the iron oxide. Episodic sedimentation can cause the deposit to have alternating bands of iron oxide and shale. Silica in the form of jasper, chert, or chalcedony can be added by chemical, clastic, or biological processes in small amounts or in significant episodes. These layered deposits of hematite and shale or hematite and silica have become known as the "banded iron formations".

Geologic Occurrence

Hematite is found as a primary mineral and as an alteration product in igneous, metamorphic, and sedimentary rocks. It can crystallize during the differentiation of a magma or precipitate from hydrothermal fluids moving through a rock mass. It can also form during contact metamorphism when hot magmas react with adjacent rocks.

The most important hematite deposits formed in sedimentary environments. About 2.4 billion years ago, Earth’s oceans were rich in dissolved iron, but very little free oxygen was present in the water. Then a group of cyanobacteria became capable of photosynthesis. The bacteria used sunlight as an energy source to convert carbon dioxide and water into carbohydrates, oxygen, and water. This reaction released the first free oxygen into the ocean environment. The new oxygen immediately combined with the iron to form hematite, which sank to the bottom of the seafloor and became the rock units that we know today as the banded iron formations.

Soon, photosynthesis was occurring in many parts of Earth’s oceans, and extensive hematite deposits were accumulating on the seafloor. This deposition continued for hundreds of millions of years - from about 2.4 to 1.8 million years ago. This allowed the formation of iron deposits hundreds to several thousand feet thick that are laterally persistent over hundreds to thousands of square miles. They comprise some of the largest rock formations in Earth’s rock record.

Many of the sedimentary iron deposits contain both hematite and magnetite as well as other iron minerals. These are often in intimate association, and the ore is mined, crushed, and processed to recover both minerals. Historically, much of the hematite was not recovered and was sent to tailings piles. More efficient processing today allows more hematite to be recovered from the ore. The tailings can also be reprocessed to recover additional iron and reduce tailings volume.

Hematite on Mars?

NASA has discovered that hematite is one of the most abundant minerals in the rocks and soils on the surface of Mars. An abundance of hematite in Martian rocks and surface materials gives the landscape a reddish brown color and is why the planet appears red in the night sky. It is the origin of Mars' "Red Planet" nickname.

Uses of Hematite (Iron Ore)

Hematite is the world’s most important ore of iron. Although magnetite contains a higher percentage of iron and is easier to process, hematite is the leading ore because it is more abundant and present in deposits in many parts of the world.

Hematite is mined in some of the largest mines in the world. These mines require investments of billions of dollars, and some will remove over 100 million tons of ore per year. These open-pit mines can be hundreds to thousands of feet deep and several miles across by the time they have been worked to completion.

China, Australia, Brazil, India, Russia, Ukraine, South Africa, and the United States are the world’s leading producers of iron ore (includes hematite, magnetite, and other ores). Iron ore production in the United States occurs in Michigan and Minnesota.

Uses of Hematite (Pigment)

The name hematite is from the Greek word "haimatitis" which means "blood-red." That name stems from the color of hematite when it has been crushed to a fine powder. Primitive people discovered that hematite could be crushed and mixed with a liquid for use as a paint or cosmetic. Cave paintings, known as "pictographs," dating back to 40,000 years ago were created with hematite pigments.

Hematite continues to be one of the most important pigment minerals. It has been mined at many locations around the world and has been traded extensively as a red pigment. During the Renaissance when many painters began using oils and canvas, hematite was one of the most important pigments. Hematite color was opaque and permanent. It could be mixed with a white pigment to produce a variety of pink colors that were used to paint flesh.

Uses of Hematite (Gem Material)

Hematite is a minor gem material used to produce cabochons, beads, small sculptures, tumbled stones, and other items. The material used to manufacture these products is a silver-colored hematite with a solid, uniform texture. The bright silver color of hematite and its "weighty feel" make it a very popular tumbled stone.

Uses of Hematite (Healing Stone)

Some people believe that carrying pieces of tumble-polished hematite, known as "healing stones," will bring relief from certain medical problems. There is no scientific proof that this use of hematite has any positive effect beyond being a placebo. Using hematite as a "healing stone" or a "healing crystal" can actually be harmful because it diverts people from seeing a doctor who can provide proper care. Then when the person with the problem finally decides to see a doctor, their situation is more severe.

Other Uses of Hematite

Hematite is used for a number of other purposes. It is a very dense and inexpensive material that is effective at stopping x-rays. For that reason it is used for radiation shielding around medical and scientific equipment. The low cost and high density of hematite and other iron ores also makes them useful as ballast for ships.

Hematite can also be ground to a fine powder that when mixed with water will make a liquid with a very high specific gravity. These liquids are used in the "float-sink" processing of coal and other mineral material. The crushed coal, which has a very low specific gravity, is placed on the heavy liquid and the light clean coal floats, while high-specific-gravity impurities such as pyrite sink.

Finally, hematite is the material used to make polishing compounds known as "red rouge" and "jeweler's rouge." Red rouge is a hematite powder used to polish brass and other soft metals. It can be added to crushed corn cob media or crushed walnut shell media for tumble-polishing brass shell casings. Jeweler's rouge is a paste used on a soft cloth to polish gold and silver jewelry.

Additional Information

Hematite, also spelled as haematite, is a common iron oxide compound with the formula Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of Fe2O3. It has the same crystal structure as corundum (Al2O3) and ilmenite (FeTiO3). With this crystal structure geometry it forms a complete solid solution at temperatures above 950 °C (1,740 °F).

Hematite occurs naturally in black to steel or silver-gray, brown to reddish-brown, or red colors. It is mined as an important ore mineral of iron. It is electrically conductive. Hematite varieties include kidney ore, martite (pseudomorphs after magnetite), iron rose and specularite (specular hematite). While these forms vary, they all have a rust-red streak. Hematite is not only harder than pure iron, but also much more brittle. The term kidney ore may be broadly used to describe botryoidal, mammillary, or reniform hematite.[8] Maghemite is a polymorph of hematite (γ-Fe2O3) with the same chemical formula, but with a spinel structure like magnetite.

Large deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that have still, standing water, or mineral hot springs, such as those in Yellowstone National Park in North America. The mineral may precipitate in the water and collect in layers at the bottom of the lake, spring, or other standing water. Hematite can also occur in the absence of water, usually as the result of volcanic activity.

Clay-sized hematite crystals also may occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or oxyhydroxides such as goethite, which is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.

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#10793. What does the term in Biology Infection mean?

#10794. What does the term in Biology Insulin mean?

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#2596. What does the medical term Erythromelalgia, or Mitchell's disease  mean?

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#6375.

2522) Automobile

Gist

An automobile is a wheeled, self-propelled motor vehicle designed primarily for transporting passengers on roads, typically featuring four wheels and an engine. Developed in the late 19th century, these vehicles have evolved from early internal combustion models to include modern electric powertrains. There are over 1.6 billion cars in use worldwide, profoundly influencing global transportation and industry.

An automobile is a self-propelled, wheeled motor vehicle primarily designed for transporting people on roads, commonly featuring four wheels and powered by an internal combustion engine or electric motor, though the term also covers vehicles like trucks and motorcycles. Essentially, it's a "self-moving" vehicle, combining the Greek auto (self) and Latin mobilis (movable). 

Summary

A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat 1-8 people, have four wheels, and mainly transport people rather than cargo. There are over 1.6 billion cars in use worldwide as of 2025.

The French inventor Nicolas-Joseph Cugnot built the first steam-powered road vehicle in 1769, while the Swiss inventor François Isaac de Rivaz designed and constructed the first internal combustion-powered automobile in 1808. The modern car—a practical, marketable automobile for everyday use—was invented in 1886, when the German inventor Carl Benz patented his Benz Patent-Motorwagen. Commercial cars became widely available during the 20th century. The 1901 Oldsmobile Curved Dash and the 1908 Ford Model T, both American cars, are widely considered the first mass-produced and mass-affordable cars, respectively. Cars were rapidly adopted in the US, where they replaced horse-drawn carriages. In Europe and other parts of the world, demand for automobiles did not increase until after World War II. In the 21st century, car usage is still increasing rapidly, especially in China, India, and other newly industrialised countries.

Cars have controls for driving, parking, passenger comfort, and a variety of lamps. Over the decades, additional features and controls have been added to vehicles, making them progressively more complex. These include rear-reversing cameras, air conditioning, navigation systems, and in-car entertainment. Most cars in use in the early 2020s are propelled by an internal combustion engine, fueled by the combustion of fossil fuels. Electric cars, which were invented early in the history of the car, became commercially available in the 2000s and widespread in the 2020s. The transition from fossil-fuel-powered cars to electric cars is a central feature of most climate change mitigation scenarios.

There are costs and benefits to car use. The costs to the individual include acquiring the vehicle, interest payments (if the car is financed), repairs and maintenance, fuel, depreciation, driving time, parking fees, taxes, and insurance. The costs to society include resources used to produce cars and fuel, maintaining roads, land-use, road congestion, air pollution, noise pollution, public health, and disposing of the vehicle at the end of its life. Traffic collisions are the largest cause of injury-related deaths worldwide. Personal benefits include on-demand transportation, mobility, independence, and convenience. Societal benefits include economic benefits, such as job and wealth creation from the automotive industry, transportation provision, and societal wellbeing from leisure and travel opportunities. People's ability to move flexibly from place to place has far-reaching implications for society.

Details

An automobile is a usually four-wheeled vehicle designed primarily for passenger transportation and commonly propelled by an internal-combustion engine using a volatile fuel.

Automotive design

The modern automobile is a complex technical system employing subsystems with specific design functions. Some of these consist of thousands of component parts that have evolved from breakthroughs in existing technology or from new technologies such as electronic computers, high-strength plastics, and new alloys of steel and nonferrous metals. Some subsystems have come about as a result of factors such as air pollution, safety legislation, and competition between manufacturers throughout the world.

Passenger cars have emerged as the primary means of family transportation, with an estimated 1.4 billion in operation worldwide. About one-quarter of these are in the United States, where more than three trillion miles (almost five trillion kilometres) are traveled each year. In recent years, Americans have been offered hundreds of different models, about half of them from foreign manufacturers. To capitalize on their proprietary technological advances, manufacturers introduce new designs ever more frequently. With some 70 million new units built each year worldwide, manufacturers have been able to split the market into many very small segments that nonetheless remain profitable.

New technical developments are recognized to be the key to successful competition. Research and development engineers and scientists have been employed by all automobile manufacturers and suppliers to improve the body, chassis, engine, drivetrain, control systems, safety systems, and emission-control systems.

These outstanding technical advancements are not made without economic consequences. According to a study by Ward’s Communications Incorporated, the average cost for a new American car increased $4,700 (in terms of the value of the dollar in 2000) between 1980 and 2001 because of mandated safety and emission-control performance requirements (such as the addition of air bags and catalytic converters). New requirements continued to be implemented in subsequent years. The addition of computer technology was another factor driving up car prices, which increased by 29 percent between 2009 and 2019. This is in addition to the consumer costs associated with engineering improvements in fuel economy, which may be offset by reduced fuel purchases.

Vehicle design depends to a large extent on its intended use. Automobiles for off-road use must be durable, simple systems with high resistance to severe overloads and extremes in operating conditions. Conversely, products that are intended for high-speed, limited-access road systems require more passenger comfort options, increased engine performance, and optimized high-speed handling and vehicle stability. Stability depends principally on the distribution of weight between the front and rear wheels, the height of the centre of gravity and its position relative to the aerodynamic centre of pressure of the vehicle, suspension characteristics, and the selection of which wheels are used for propulsion. Weight distribution depends principally on the location and size of the engine. The common practice of front-mounted engines exploits the stability that is more readily achieved with this layout. The development of aluminum engines and new manufacturing processes has, however, made it possible to locate the engine at the rear without necessarily compromising stability.

Body

Automotive body designs are frequently categorized according to the number of doors, the arrangement of seats, and the roof structure. Automobile roofs are conventionally supported by pillars on each side of the body. Convertible models with retractable fabric tops rely on the pillar at the side of the windshield for upper body strength, as convertible mechanisms and glass areas are essentially nonstructural. Glass areas have been increased for improved visibility and for aesthetic reasons.

The high cost of new factory tools makes it impractical for manufacturers to produce totally new designs every year. Completely new designs usually have been programmed on three- to six-year cycles with generally minor refinements appearing during the cycle. In the past, as many as four years of planning and new tool purchasing were needed for a completely new design. Computer-aided design (CAD), testing by use of computer simulations, and computer-aided manufacturing (CAM) techniques may now be used to reduce this time requirement by 50 percent or more. See machine tool: Computer-aided design and computer-aided manufacturing (CAD/CAM).

Automotive bodies are generally formed out of sheet steel. The steel is alloyed with various elements to improve its ability to be formed into deeper depressions without wrinkling or tearing in manufacturing presses. Steel is used because of its general availability, low cost, and good workability. For certain applications, however, other materials, such as aluminum, fibreglass, and carbon-fibre reinforced plastic, are used because of their special properties. Polyamide, polyester, polystyrene, polypropylene, and ethylene plastics have been formulated for greater toughness, dent resistance, and resistance to brittle deformation. These materials are used for body panels. Tooling for plastic components generally costs less and requires less time to develop than that for steel components and therefore may be changed by designers at a lower cost.

To protect bodies from corrosive elements and to maintain their strength and appearance, special priming and painting processes are used. Bodies are first dipped in cleaning baths to remove oil and other foreign matter. They then go through a succession of dip and spray cycles. Enamel and acrylic lacquer are both in common use. Electrodeposition of the sprayed paint, a process in which the paint spray is given an electrostatic charge and then attracted to the surface by a high voltage, helps assure that an even coat is applied and that hard-to-reach areas are covered. Ovens with conveyor lines are used to speed the drying process in the factory. Galvanized steel with a protective zinc coating and corrosion-resistant stainless steel are used in body areas that are more likely to corrode.

Chassis

In most passenger cars through the middle of the 20th century, a pressed-steel frame—the vehicle’s chassis—formed a skeleton on which the engine, wheels, axle assemblies, transmission, steering mechanism, brakes, and suspension members were mounted. The body was flexibly bolted to the chassis during a manufacturing process typically referred to as body-on-frame construction. This process is used today for heavy-duty vehicles, such as trucks, which benefit from having a strong central frame, subjected to the forces involved in such activities as carrying freight, including the absorption of the movements of the engine and axle that is allowed by the combination of body and frame.

In modern passenger-car designs, the chassis frame and the body are combined into a single structural element. In this arrangement, called unit-body (or unibody) construction, the steel body shell is reinforced with braces that make it rigid enough to resist the forces that are applied to it. Separate frames or partial “stub” frames have been used for some cars to achieve better noise-isolation characteristics. The heavier-gauge steel present in modern component designs also tends to absorb energy during impacts and limit intrusion in accidents.

Engine

A wide range of engines has been used experimentally and in automotive production. The most successful for automobiles has been the gasoline-fueled reciprocating-piston internal-combustion engine, operating on a four-stroke cycle, while diesel engines are widely used for trucks and buses. The gasoline engine was originally selected for automobiles because it could operate more flexibly over a wide range of speeds, and the power developed for a given weight engine was reasonable; it could be produced by economical mass-production methods; and it used a readily available, moderately priced fuel. Reliability, compact size, exhaust emissions, and range of operation later became important factors.

There has been an ongoing reassessment of these priorities with new emphasis on the reduction of greenhouse gases (see greenhouse effect) or pollution-producing characteristics of automotive power systems. This has created new interest in alternate power sources and internal-combustion engine refinements that previously were not close to being economically feasible. Several limited-production battery-powered electric vehicles are marketed today. In the past they had not proved to be competitive, because of costs and operating characteristics. The gasoline engine, with new emission-control devices to improve emission performance, has been challenged in recent years by hybrid power systems that combine gasoline or diesel engines with battery systems and electric motors. Such designs are, however, more complex and therefore more costly.

The evolution of higher-performance engines in the United States led the industry away from long, straight engine cylinder layouts to compact six- and eight-cylinder V-type layouts for larger cars (with horsepower ratings up to about 350). Smaller cars depend on smaller four-cylinder engines. European automobile engines were of a much wider variety, ranging from 1 to 12 cylinders, with corresponding differences in overall size, weight, piston displacement, and cylinder bores. A majority of the models had four cylinders and horsepower ratings up to 120. Most engines had straight or in-line cylinders. There were, however, several V-type models and horizontally opposed two- and four-cylinder makes. Overhead camshafts were frequently employed. The smaller engines were commonly air-cooled and located at the rear of the vehicle; compression ratios were relatively low. Increased interest in improved fuel economy brought a return to smaller V-6 and four-cylinder layouts, with as many as five valves per cylinder to improve efficiency. Variable valve timing to improve performance and lower emissions has been achieved by manufacturers in all parts of the world. Electronic controls automatically select the better of two profiles on the same cam for higher efficiency when engine speeds and loads change.

Fuel

Specially formulated gasoline is essentially the only fuel used for automobile operation, although diesel fuels are used for many trucks and buses and a few automobiles, and compressed liquefied hydrogen has been used experimentally. The most important requirements of a fuel for automobile use are proper volatility, sufficient antiknock quality, and freedom from polluting by-products of combustion. The volatility is reformulated seasonally by refiners so that sufficient gasoline vaporizes, even in extremely cold weather, to permit easy engine starting. Antiknock quality is rated by the octane number of the gasoline. The octane number requirement of an automobile engine depends primarily on the compression ratio of the engine but is also affected by combustion-chamber design, the maintenance condition of engine systems, and chamber-wall deposits. In the 21st century regular gasoline carried an octane rating of 87 and high-test in the neighbourhood of 93.

Automobile manufacturers have lobbied for regulations that require the refinement of cleaner-burning gasolines, which permit emission-control devices to work at higher efficiencies. Such gasoline was first available at some service stations in California, and from 2017 the primary importers and refiners of gasoline throughout the United States were required to remove sulfur particles from fuel to an average level of 10 parts per million (ppm).

Vehicle fleets fueled by natural gas have been in operation for several years. Carbon monoxide and particulate emissions are reduced by 65 to 90 percent. Natural-gas fuel tanks must be four times larger than gasoline tanks for equivalent vehicles to have the same driving range. This compromises cargo capacity.

Ethanol (ethyl alcohol) is often blended with gasoline (15 parts to 85 parts) to raise its octane rating, which results in a smoother-running engine. Ethanol, however, has a lower energy density than gasoline, which results in decreased range per tankful.

Lubrication

All moving parts of an automobile require lubrication. Without it, friction would increase power consumption and damage the parts. The lubricant also serves as a coolant, a noise-reducing cushion, and a sealant between engine piston rings and cylinder walls. The engine lubrication system incorporates a gear-type pump that delivers filtered oil under pressure to a system of drilled passages leading to various bearings. Oil spray also lubricates the cams and valve lifters.

Wheel bearings and universal joints require a fairly stiff grease; other chassis joints require a soft grease that can be injected by pressure guns. Hydraulic transmissions require a special grade of light hydraulic fluid, and manually shifted transmissions use a heavier gear oil similar to that for rear axles to resist heavy loads on the gear teeth. Gears and bearings in lightly loaded components, such as generators and window regulators, are fabricated from self-lubricating plastic materials. Hydraulic fluid is also used in other vehicle systems in conjunction with small electric pumps and motors.

Cooling system

Almost all automobiles employ liquid cooling systems for their engines. A typical automotive cooling system comprises (1) a series of channels cast into the engine block and cylinder head, surrounding the combustion chambers with circulating water or other coolant to carry away excessive heat, (2) a radiator, consisting of many small tubes equipped with a honeycomb of fins to radiate heat rapidly, which receives and cools hot liquid from the engine, (3) a centrifugal-type water pump with which to circulate coolant, (4) a thermostat, which maintains constant temperature by automatically varying the amount of coolant passing into the radiator, and (5) a fan, which draws fresh air through the radiator.

For operation at temperatures below 0 °C (32 °F), it is necessary to prevent the coolant from freezing. This is usually done by adding some compound, such as ethylene glycol, to depress the freezing point of the coolant. By varying the amount of additive, it is possible to protect against freezing of the coolant down to any minimum temperature normally encountered. Coolants contain corrosion inhibitors designed to make it necessary to drain and refill the cooling system only every few years.

Air-cooled cylinders operate at higher, more efficient temperatures, and air cooling offers the important advantage of eliminating not only freezing and boiling of the coolant at temperature extremes but also corrosion damage to the cooling system. Control of engine temperature is more difficult, however, and high-temperature-resistant ceramic parts are required when design operating temperatures are significantly increased.

Pressurized cooling systems have been used to increase effective operating temperatures. Partially sealed systems using coolant reservoirs for coolant expansion if the engine overheats were introduced in the early 1970s. Specially formulated coolants that do not deteriorate over time eliminate the need for annual replacement.

Electrical system

The electrical system comprises a storage battery, generator, starting (cranking) motor, lighting system, ignition system, and various accessories and controls. Originally, the electrical system of the automobile was limited to the ignition equipment. With the advent of the electric starter on a 1912 Cadillac model, electric lights and horns began to replace the kerosene and acetylene lights and the bulb horns. Electrification was rapid and complete, and, by 1930, 6-volt systems were standard everywhere.

Increased engine speeds and higher cylinder pressures made it increasingly difficult to meet high ignition voltage requirements. The larger engines required higher cranking torque. Additional electrically operated features—such as radios, window regulators, and multispeed windshield wipers—also added to system requirements. To meet these needs, 12-volt systems replaced the 6-volt systems in the late 1950s around the world.

The ignition system provides the spark to ignite the air-fuel mixture in the cylinders of the engine. The system consists of the spark plugs, coil, distributor, and battery. In order to jump the gap between the electrodes of the spark plugs, the 12-volt potential of the electrical system must be stepped up to about 20,000 volts. This is done by a circuit that starts with the battery, one side of which is grounded on the chassis and leads through the ignition switch to the primary winding of the ignition coil and back to the ground through an interrupter switch. Interrupting the primary circuit induces a high voltage across the secondary terminal of the coil. The high-voltage secondary terminal of the coil leads to a distributor that acts as a rotary switch, alternately connecting the coil to each of the wires leading to the spark plugs.

Solid-state or transistorized ignition systems were introduced in the 1970s. These distributor systems provided increased durability by eliminating the frictional contacts between breaker points and distributor cams. The breaker point was replaced by a revolving magnetic-pulse generator in which alternating-current pulses trigger the high voltage needed for ignition by means of an amplifier electronic circuit. Changes in engine ignition timing are made by vacuum or electronic control unit (microprocessor) connections to the distributor.

The source of energy for the various electrical devices of the automobile is a generator, or alternator, that is belt-driven from the engine crankshaft. The design is usually an alternating-current type with built-in rectifiers and a voltage regulator to match the generator output to the electric load and also to the charging requirements of the battery, regardless of engine speed.

A lead-acid battery serves as a reservoir to store excess output of the generator. This provides energy for the starting motor and power for operating other electric devices when the engine is not running or when the generator speed is not sufficiently high for the load.

The starting motor drives a small spur gear so arranged that it automatically moves in to mesh with gear teeth on the rim of the flywheel as the starting-motor armature begins to turn. When the engine starts, the gear is disengaged, thus preventing damage to the starting motor from overspeeding. The starting motor is designed for high current consumption and delivers considerable power for its size for a limited time.

Headlights must satisfactorily illuminate the highway ahead of the automobile for driving at night or in inclement weather without temporarily blinding approaching drivers. This was achieved in modern cars with double-filament bulbs with a high and a low beam, called sealed-beam units. Introduced in 1940, these bulbs found widespread use following World War II. Such units could have only one filament at the focal point of the reflector. Because of the greater illumination required for high-speed driving with the high beam, the lower beam filament was placed off centre, with a resulting decrease in lighting effectiveness. Separate lamps for these functions can also be used to improve illumination effectiveness.

Dimming is automatically achieved on some cars by means of a photocell-controlled switch in the lamp circuit that is triggered by the lights of an oncoming car. Lamp clusters behind aerodynamic plastic covers permitted significant front-end drag reduction and improved fuel economy. In this arrangement, steerable headlights became possible with an electric motor to swivel the lamp assembly in response to steering wheel position. The regulations of various governments dictate brightness and field of view requirements for vehicle lights.

Signal lamps and other special-purpose lights have increased in usage since the 1960s. Amber-coloured front and red rear signal lights are flashed as a turn indication; all these lights are flashed simultaneously in the “flasher” (hazard) system for use when a car is parked along a roadway or is traveling at a low speed on a high-speed highway. Marker lights that are visible from the front, side, and rear also are widely required by law. Red-coloured rear signals are used to denote braking, and cornering lamps, in connection with turning, provide extra illumination in the direction of an intended turn. Backup lights provide illumination to the rear and warn anyone behind the vehicle when the driver is backing up. High-voltage light-emitting diodes (LEDs) have been developed for various signal and lighting applications.

Transmission

The gasoline engine must be disconnected from the driving wheels when it is started and when idling. This characteristic necessitates some type of unloading and engaging device to permit gradual application of load to the engine after it has been started. The torque, or turning effort, that the engine is capable of producing is low at low crankshaft speeds, increasing to a maximum at some fairly high speed representing the maximum, or rated, horsepower.

The efficiency of an automobile engine is highest when the load on the engine is high and the throttle is nearly wide open. At moderate speeds on level pavement, the power required to propel an automobile is only a fraction of this. Under normal driving conditions at constant moderate speed, the engine may operate at an uneconomically light load unless some means is provided to change its speed and power output.

The transmission is such a speed-changing device. Installed in the power train between the engine and the driving wheels, it permits the engine to operate at a higher speed when its full power is needed and to slow down to a more economical speed when less power is needed. Under some conditions, as in starting a stationary vehicle or in ascending steep grades, the torque of the engine is insufficient, and amplification is needed. Most devices employed to change the ratio of the speed of the engine to the speed of the driving wheels multiply the engine torque by the same factor by which the engine speed is increased.

The simplest automobile transmission is the sliding-spur gear type with three or more forward speeds and reverse. The desired gear ratio is selected by manipulating a shift lever that slides a spur gear into the proper position to engage the various gears. A clutch is required to engage and disengage gears during the selection process. The necessity of learning to operate a clutch is eliminated by an automatic transmission. Most automatic transmissions employ a hydraulic torque converter, a device for transmitting and amplifying the torque produced by the engine. Each type provides for manual selection of reverse and low ranges that either prevent automatic upshifts or employ lower gear ratios than are used in normal driving. Grade-retard provisions are also sometimes included to supply dynamic engine braking on hills. Automatic transmissions not only require little skill to operate but also make possible better performance than is obtainable with designs that require clutch actuation.

In hydraulic transmissions, shifting is done by a speed-sensitive governing device that changes the position of valves that control the flow of hydraulic fluid. The vehicle speeds at which shifts occur depend on the position of the accelerator pedal, and the driver can delay upshifts until higher speed is attained by depressing the accelerator pedal further. Control is by hydraulically engaged bands and multiple-disk clutches running in oil, either by the driver’s operation of the selector lever or by speed- and load-sensitive electronic control in the most recent designs. Compound planetary gear trains with multiple sun gears and planet pinions have been designed to provide a low forward speed, intermediate speeds, a reverse, and a means of locking into direct drive. This unit is used with various modifications in almost all hydraulic torque-converter transmissions. All transmission control units are interconnected with vehicle emission control systems that adjust engine timing and air-to-fuel ratios to reduce exhaust emissions.

Oil in the housing is accelerated outward by rotating vanes in the pump impeller and, reacting against vanes in the turbine impeller, forces them to rotate, as shown schematically in the figure. The oil then passes into the stator vanes, which redirect it to the pump. The stator serves as a reaction member providing more torque to turn the turbine than was originally applied to the pump impeller by the engine. Thus, it acts to multiply engine torque by a factor of up to 2 1/2 to 1.

Blades in all three elements are specially contoured for their specific function and to achieve particular multiplication characteristics. Through a clutch linkage, the stator is allowed gradually to accelerate until it reaches the speed of the pump impeller. During this period torque multiplication gradually drops to approach 1 to 1.

The hydraulic elements are combined with two or more planetary gear sets, which provide further torque multiplication between the turbine and the output shaft.

Continuously (or infinitely) variable transmissions provide a very efficient means of transferring engine power and, at the same time, automatically changing the effective input-to-output ratio to optimize economy by keeping the engine running within its best power range. Most designs employ two variable-diameter pulleys connected by either a steel or high-strength rubber V-belt. The pulleys are split so that effective diameters may be changed by an electrohydraulic actuator to change the transmission ratio. This permits the electronic control unit to select the optimum ratio possible for maximum fuel economy and minimum emissions at all engine speeds and loads. Originally these units were limited to small cars, but belt improvements have made them suitable for larger cars.

Additional Information

The four-wheeled transportation vehicle symbolizes the promise and the pitfalls of the modern age.

An automobile is a self-propelled motor vehicle intended for passenger transportation on land. It usually has four wheels and an internal combustion engine fueled most often by gasoline, a liquid petroleum product. Known more commonly as a car, formerly as a motorcar, it is one of the most universal of modern technologies, manufactured by one of the world’s largest industries. More than 73 million new automobiles were produced worldwide in the year 2017.

The scientific and technical building blocks of the automobile go back several hundred years. For example, in the late 1600s, Dutch scientist Christiaan Huygens invented a type of internal combustion engine sparked by gunpowder. The “horseless carriage” in its modern form had been developed by the end of the 19th century. At that time, it was not clear which of three fuel sources would become most commercially successful: steam, electric power, or gasoline. Cars run by steam engines could go at high speeds but had a short range and were inconvenient to start. Battery-powered electric cars had a 38 percent share of the United States automobile market in 1900, but they also had a limited range and recharging stations were hard to find.

The gasoline-powered automobile won the competition. By 1920, it had overtaken the streets and byways of Europe and the United States. The manufacturing methods introduced by U.S. carmaker Henry Ford revolutionized industrial manufacturing. Ford was the first to install assembly lines in his factory to speed up production. Such techniques reduced the price of Ford’s Model T until it became affordable for most middle-class families. As the 20th century progressed, modern life came to seem increasingly inconceivable, or at least highly inconvenient, without access to a car. Nowadays, the U.S. population drives more than 4.8 trillion kilometers (three trillion miles) every year on average.

But this fundamental component of industrial and consumer society has played a major role in destabilizing Earth’s atmosphere, on which all living things depend. The average automobile emits between four and nine tons (3,629 to 8,165 kilograms; 8,000 to 18,000 pounds) of carbon dioxide and other greenhouse gases per year. Every gallon of gasoline burned to operate a car emits just under 9.1 kilograms (20 pounds) of carbon dioxide. The transportation sector as a whole, including cars, trucks, trains, and aircraft, became the largest source of U.S. greenhouse gas emissions in 2017. Air pollution from automobile exhaust is also a major problem, as are car accidents, which killed more than 100 people per day in the United States in 2016, according to the National Highway Traffic Safety Administration.