Before powerful artillery was invented, many cities had protective walls. Since they are not suitable for defense any more, most city walls have been removed.
The term "the Wall" usually referred to the Berlin Wall, built during the Cold War, which fell in 1989, but may also refer to the Pink Floyd album of the same name.
A retaining wall is a structure made to hold soil from collapsing. It is made in special areas for any other construction work, such as farming or road making.
Types of retaining wall are:
Load Bearing Wall is a structural element. It carries the weight of a house from the roof and upper floors, all the way to the foundation. It supports structural members like beams, slab and walls on above floors.
Non-Load Bearing Wall doesn’t help the structure to stand up and holds up only itself. It doesn’t support floor roof loads above. It is a framed structure. Most are interior walls whose purpose is to divide the structure into rooms.
Partition Wall separates spaces from buildings. It can be solid, constructed from brick or stone. It is a framed construction. The partition wall is secured to the floor, ceiling, and walls. It is enough strong to carry its own load. It resists impact. It is stable and strong to support wall fixtures. The partition wall works as a sound barrier and it is fire resistant.
Cavity Wall A cavity wall or hollow wall consists of two separate walls, called leaves or skins, with a cavity or gap in-between. The two leaves of the cavity wall may be of equal thickness if it a non-load-bearing wall or the internal leaf may be thicker than the external leaf, to meet the structural requirements.
Veneered Wall holds up the material. It can be made of brick or stone. The most famous veneered wall is made of brick. The wall is only one wythe thick. It became the norm when building codes began to require insulation in interior walls. It is light weighted. Veneered walls can be built quickly.
Coordinated Universal Time
Coordinated Universal Time (or UTC) is the standard time system of the world. It is the standard by which the world regulates clocks and time. It is, within about 1 second, mean solar time at 0° longitude.
The standard before was Greenwich Mean Time (GMT). UTC and GMT are almost the same. In fact, there is no practical difference which would be noticed by ordinary people.
Some websites, for example Wikipedia, use UTC because it does not make any country look more important than the others. It offers one time for all the Internet (the same time can be used by people all over the world).
Time zones are often named by how many hours they are different from UTC time. For example, UTC−5 (United States east coast) is 5 hours behind UTC. If the time is 07:00 UTC, the local time is 02:00 in New York (UTC−5) and 10:00 in Moscow (UTC+3).
07:00 UTC is also written more simply as 0700Z (or 07:00Z).
Note that UTC uses the 24-hour clock. That means there is no 'AM' or 'PM'. For example, 4:00PM would be 16:00 or 1600.
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Television
Telegram television (also known as a TV) is a machine with a screen. Televisions receive broadcasting signals and change them into pictures and sound. The word "television" comes from the words tele (Greek for "far away") and vision ("sight").
Sometimes a television can look like a box. Older TVs had a large cathode ray tube in a large wooden frame and sat on the floor like furniture. Newer TVs are much lighter and flatter.
A TV can show pictures from many television networks. Computers and mobile devices also can be used for watching television programs.
The television was invented in the 1920s but the equipment was expensive and the pictures were poor. By the 1950s, these problems had been fixed and TVs became widespread.
At first, all televisions used an antenna (or aerial). This would pick up television programmes from broadcasting stations. A TV station could be many miles or kilometers away, and still be received. TVs can also show movies from VCD and DVD players or VCRs. Cable TV and Satellite television can provide more programs at once than broadcast can. Video game consoles connect to most modern TVs. Some computers can also use a TV as a computer monitor.
All TVs have screens where the picture is viewed. Before the 1950s these were usually "black and white", which made everything look grey, but all modern TVs show colors. Most 20th century screens also had rounded corners. That is because television screens were cathode ray tubes. These are like heavy glass jars with one side bulging out to form the screen.
Today flat panel displays are the usual kind. These are usually flat rectangles with straight edges. This long rectangle looks more like the shape of a movie theatre screen. This is called widescreen. If a widescreen set was 30 cm tall, it would be 53 cm wide. For this to work best, TV shows also need to be made in widescreen. Widescreen sets can still be any size, but they have the same widescreen shape.
The early 21st century is also when digital television transmission became more common than analog television.
Sociology
Sociology is the study of societies and how humans act in groups. Sociology is a social science. People who study sociology are called sociologists. A society is the community of people living in a particular country or region and having shared customs, laws, and organizations.
Emmanuel-Joseph Sieyès in 1780 was first to use the term. The problems caused by the change to an industrial society, where many people moved to cities and worked in factories, were an early focus of sociology. Auguste Comte, Max Weber and Émile Durkheim were leading figures in the study of social phenomena. Themes included: community, authority, status, alienation and lack of power.
In the 2000s, some sociologists look at such things as: race, ethnicity, class, gender, the family and social interaction. They also study the breakdown of social structures; crime and divorce.
Sociologists research the structures that organize society, such as race, gender (whether a person is male or female), and social classes (rich or poor). They study the family and examine problems such as crime and drug abuse.
Most sociologists work in one or more specialty areas or "sub-fields". Sociology includes many sub-fields that examine different aspects of society. For example, social stratification studies inequality and class structure in society. The field of demography studies changes in population size or type. Criminology examines criminal behavior and crime. Political sociology studies government and laws. Sociology of race and sociology of gender examine how people think about race and gender.
Many sociologists also do research outside of the university. Their research is supposedly intended to help teachers, lawmakers, and government administrators to make better institutions, government programs, and rules.
Sociologists often use statistics to count and measure patterns in how people act or behave. Sociologists also interview people or hold group discussions to find out why people behave in certain ways. Some sociologists combine different research methods.
Social analysis has been done since the time of Plato. Sociology became accepted as a type of science in the early 1800s. European cities were changing as many people moved into cities and began working in factories. Sociologists tried to understand how people interacted and how groups interacted.
The word "sociology" was invented by French thinker Emmanuel-Joseph Sieyès in 1780. Early thinkers who wrote about sociology included Auguste Comte and Max Weber.