Twelve or 12 may refer to:
- 12 (number)
- December, the twelfth and final month of the year
- Dozen, a group of twelve.
A brush is a common tool with bristles, wire or other filaments. It generally consists of a handle or block to which filaments are affixed in either a parallel or perpendicular orientation, depending on the way the brush is to be gripped during use. The material of both the block and bristles or filaments is chosen to withstand hazards of its intended use, such as corrosive chemicals, heat or abrasion. It is used for cleaning, grooming hair, make up, painting, surface finishing and for many other purposes. It is one of the most basic and versatile tools in use today, and the average household may contain several dozen varieties.
A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people rather than cargo. There are around one billion cars in use worldwide.
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 are predicted to cost less to buy than petrol-driven cars before 2025. The transition from fossil fuel-powered cars to electric cars features prominently in most climate change mitigation scenarios, such as Project Drawdown's 100 actionable solutions for climate change.
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 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, societal well-being from leisure and travel opportunities. People's ability to move flexibly from place to place has far-reaching implications for the nature of societies.
A cleaner, cleanser or cleaning operative is a type of industrial or domestic worker who is tasked with cleaning a space. A janitor (US and Canada), also known as a custodian, Facility Operator, porter or caretaker, is a person who cleans and might also carry out maintenance and security duties. A similar position, but usually with more managerial duties and not including cleaning, is occupied by building superintendents in the United States and Canada and by site managers in schools in the United Kingdom.
According to the Cambridge English dictionary a "cleaner" is "a person whose job is to clean houses, offices, public places, etc.:"; the Collins dictionary states that: "A cleaner is someone who is employed to clean the rooms and furniture inside a building." However, a cleaner does not always have to be employed and perform work for pay, such as in the case of volunteer work or community service. "Cleaner" may also refer to cleaning agents e.g. oven cleaner, or devices used for cleaning, e.g. vacuum cleaner.
Cleaning operatives may specialize in cleaning particular things or places, such as window cleaners, housekeepers, janitors, crime scene cleaners and so on. Cleaning operatives often work when the people who otherwise occupy the space are not around. They may clean offices at night or houses during the workday.
Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning is often performed for aesthetic, hygienic, functional, safety, or environmental protection purposes. Cleaning occurs in many different contexts, and uses many different methods. Several occupations are devoted to cleaning.
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power generation), heat energy (e.g. geothermal), chemical energy, electric potential and nuclear energy (from nuclear fission or nuclear fusion). Many of these processes generate heat as an intermediate energy form; thus heat engines have special importance. Some natural processes, such as atmospheric convection cells convert environmental heat into motion (e.g. in the form of rising air currents). Mechanical energy is of particular importance in transportation, but also plays a role in many industrial processes such as cutting, grinding, crushing, and mixing.
Mechanical heat engines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common example of a mechanical heat engine in which heat from the combustion of a fuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft. Unlike internal combustion engines, a reaction engine (such as a jet engine) produces thrust by expelling reaction mass, in accordance with Newton's third law of motion.
Apart from heat engines, electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and ultimately motion (a chemical engine, but not a heat engine).
Chemical heat engines which employ air (ambient atmospheric gas) as a part of the fuel reaction are regarded as airbreathing engines. Chemical heat engines designed to operate outside of Earth's atmosphere (e.g. rockets, deeply submerged submarines) need to carry an additional fuel component called the oxidizer (although there exist super-oxidizers suitable for use in rockets, such as fluorine, a more powerful oxidant than oxygen itself); or the application needs to obtain heat by non-chemical means, such as by means of nuclear reactions.
Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hogs, ostriches, and aquatic animals such as seals and alligators.
Leather can be used to make a variety of items, including clothing, footwear, handbags, furniture, tools and sports equipment, and lasts for decades. Leather making has been practiced for more than 7,000 years and the leading producers of leather today are China and India.
Critics of tanneries claim that they engage in unsustainable practices that pose health hazards to the people and the environment near them.
A motorcycle (motorbike, bike, or, if three-wheeled, a trike) is a two or three-wheeled motor vehicle steered by a handlebar from a saddle-style seat.
Motorcycle designs vary greatly to suit a range of different purposes: long-distance travel, commuting, cruising, sport (including racing), and off-road riding. Motorcycling is riding a motorcycle and being involved in other related social activities such as joining a motorcycle club and attending motorcycle rallies.
The 1885 Daimler Reitwagen made by Gottlieb Daimler and Wilhelm Maybach in Germany was the first internal combustion, petroleum-fueled motorcycle. In 1894, Hildebrand & Wolfmüller became the first series production motorcycle.
Globally, motorcycles are comparable numerically to cars as a method of transport: in 2021, approximately 58.6 million new motorcycles were sold around the world, while 66.7 million cars were sold over the same period.
In 2022, the top four motorcycle producers by volume and type were Honda, Yamaha, Kawasaki, and Suzuki.
According to the US Department of Transportation, the number of fatalities per vehicle mile traveled was 37 times higher for motorcycles than for cars.
A wheel is a rotating component (typically circular in shape) that is intended to turn on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be moved easily facilitating movement or transportation while supporting a load, or performing labor in machines. Wheels are also used for other purposes, such as a ship's wheel, steering wheel, potter's wheel, and flywheel.
Common examples can be found in transport applications. A wheel reduces friction by facilitating motion by rolling together with the use of axles. In order for wheels to rotate, a moment needs to be applied to the wheel about its axis, either by way of gravity or by the application of another external force or torque.
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