centrifugal force

a force that divides people and countries

centripital force
a force that unites people and countries
common market
a group of countries that acts as a single market, without trade borders between member countries.
supernatural cooperation
a form of international cooperation in which countries give up some control of their affairs as they work together to achieve shared goals.
the study of human populations, including how they change due to births, deaths, aging, and migration.

dependency ratio

the number of old and young dependents who don’t work compared with the working age population. The higher the ratio, the more young and old people the workers have to support.
life expectancy
the average age that a person in a given population can expect to live. Life expectancy varies from one country to another.

replacement rate

The toal fertility rate needed for a population to replace itself. This number varies by country, but is about 2.1 in most developed countries.

total fertility rate

The average number of children a woman in a given population will have in her lifetime. This number is different in different countries.

acid rain

Rain that can;damadge the environment because it contains acid from car exhaust and factory smoke. Acid rain can damadge plants, fish, animals, and even buildings.
Nuclear Radiation
A form of energy that comes from nuclear reactions. Radiation has no smell or taste, but can be very harmful to living things. Materials polluted with nuclear radiation are said to be radioactive.
River System
A river and all the streams that flow into it. The streams that flow into a river are called tributaries.
Transboundary Pollution
Pollution that starts in one country and crosses borders into other countries. Generally, transboundary pollution is carried by wind or water.
The gradual wearing away of Earth’s surface by the action of wind, water, ice, and gravity.
The creation and movement of glaciers.
Physical Process
Natural forces that change Earth’s physical features including forces that build up and wear down Earth’s surface.
Tectonic Movement
The movement of plates below the Earth’s surface.
Volcanic Activity
The formation and eruption of volcanoes.

Ethnic Group

A group of people in a country who share a unique culture and identity.
A large group of people who share a common history and culture. Not all nations have their own government or control territory. But in common use the word nation often means a country or nation-state.
An independent state or country whose people mostly share a common identity.
A pollitical unit that controls a particular territory.

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