mass. Even a speck of dust has a force of
gravity. But its gravity is very, very small.
The force of gravity also depends on the
distance between two objects. The
smaller the distance, the greater is the
force of gravity between them.
#More to explore
Newton, Isaac • Solar System
Great Barrier
Reef
The Great Barrier Reef is the largest
coral reef on Earth. A barrier reef is a
long, narrow coral formation that lies
parallel to the shoreline of a landmass
and is mostly underwater. The Great
Barrier Reef is in the Coral Sea, off the
northeastern coast of Australia. It
extends 1,250 miles (2,000 kilometers)
from north to south.
The Great Barrier Reef is a tourist
attraction and a protected marine environment.
The sea life of the reef is
extraordinary. The reef has been formed
over millions of years from the skeletons
of millions of tiny corals. There are at
least 300 types of hard coral on the
Great Barrier Reef. Other animals
include sponges, anemones, worms,
snails, lobsters, crayfish, prawns, jellyfish,
and giant clams. Certain algae give
the reef a purplish red rim. There are
also hundreds of different birds in the
area and more than 1,500 types of fish,
many with brilliant colors and unusual
shapes.
#More to explore
Australia • Coral
Great Britain
Great Britain is the largest island in
Europe. It contains England, Scotland,
andWales. Together with Northern Ireland,
they make up the country of the
United Kingdom of Great Britain and
Northern Ireland. Sometimes the term
Great Britain is used to refer to the
whole United Kingdom. Great Britain is
Colorful corals and fish help to create the
striking beauty of the Great Barrier Reef.
BRITANNICA STUDENT ENCYCLOPEDIA Great Britain 145
located off the northwestern coast of
mainland Europe.
#More to explore
England • Scotland • United Kingdom
•Wales
Great Depression
During the 1930s much of the world
faced harsh economic conditions. Many
people were out of work, hungry, or
homeless. This period is called the Great
Depression. It started in the United
States, but it quickly spread throughout
the world.
Effects in the United States
During the 1920s many people invested
their money in stocks (shares of ownership
in companies). For a few years the
value of stocks rose rapidly. In September
1929, however, stock prices began to
fall. On October 29 they “crashed.” This
meant that people’s stocks were now
worth almost nothing. This day became
known as Black Tuesday.
Many people lost all the money they
had. Banks were hurt as well. People
who had borrowed money from banks
were unable to pay it back. Many banks
failed because crowds of people tried to
take out all their money at once. When
a bank failed, people with accounts there
lost their savings. In addition, factories
and businesses closed because not
enough people were able to buy the
goods they produced or sold.
By 1932 about 12 to 13 million people
were out of work. People with jobs were
paid only about half of what they had
earned before. Dry weather in the Great
Plains made things even worse for farmers.
They could not grow enough crops
to sell. The land was so dry that it was
called the Dust Bowl.
Effects Around theWorld
The situation in the United States
affected countries all over the world.
The United States could no longer lend
as much money or trade as many goods
Women serve soup and bread to the unemployed
during the Great Depression.
146 Great Depression BRITANNICA STUDENT ENCYCLOPEDIA
with other countries. Great Britain, Germany,
and other countries suffered from
the loss of U.S. loans and trade.
End of the Great Depression
In the United States angry voters turned
President Herbert Hoover out of office
in 1932. The new president, Franklin D.
Roosevelt, had a program that he called
the New Deal. The New Deal put some
people back to work right away. It also
changed the financial (banking and
money) system to prevent the same
problems from happening in the future.
The Great Depression ended in the
United States only after the country
enteredWorldWar II in 1941. Factories
began to produce weapons, airplanes,
ships, and other products necessary for
the war effort. Many people were then
able to get jobs.
#More to explore
Dust Bowl • New Deal • Stock
Exchange
Great Lakes
The Great Lakes are five large lakes in
eastern North America. They are Lakes
Superior, Michigan, Huron, Erie, and
Ontario. Together the Great Lakes cover
an area of about 94,850 square miles
(245,660 square kilometers). They form
the largest connected area of freshwater
on Earth.
Lake Michigan is the only one of the
Great Lakes that is completely within
the United States. The other four form a
natural border between Canada and the
United States. Lake Superior is the largest
and the deepest of the Great Lakes.
Lake Ontario is the smallest. Lake Erie is
the shallowest. Lake Huron has the
longest shoreline.
The Great Lakes affect the climate of the
surrounding land. They absorb a lot of
heat in the summer. In the winter they
release heat into the air. As a result, the
land closest to the lakes has cooler summers
and warmer winters than areas
farther inland. Large parts of the lakes
