things at him. Pitchers sometimes threw
the ball at him on purpose. But Robinson
refused to quit.
Robinson helped the Dodgers win six
National League pennants and one
World Series title. He retired from baseball
in 1957.
Later Years
Robinson then became a businessman
and worked for civil rights. In 1962 he
became the first black player in the Base-
Jackie
Robinson’s
tombstone
reads, “A life
is not important
except in
the impact it
has on other
lives.”
Jackie Robinson played 10 seasons
for the Brooklyn Dodgers.
His lifetime batting average was
.311.
BRITANNICA STUDENT ENCYCLOPEDIA Robinson, Jackie 73
ball Hall of Fame. Robinson died in
Stamford, Connecticut, on October 24,
1972.
In 1997 Major League Baseball honored
Robinson by retiring his number 42
jersey. No other major league player can
wear that number.
#More to explore
African Americans • Baseball
Robot
A robot is a machine that does tasks
without the help of a person. Many
people think of robots as machines that
look and act like people. Most robots,
though, do not look like people. And
robots do only what a person has built
them to do.
How RobotsWork
Most robots are computer-controlled
devices with many parts. An industrial
robot, for example, is an armlike
machine that can turn at several joints.
It has a handlike part to grasp and hold
things. Motors move the parts.
Some robots can be “taught” to do a job.
For example, a person might guide an
industrial robot through the movements
needed to do something. Sensors on the
robot send signals about the movements
to the computer. The computer stores
the pattern of movements. Later the
computer can retrieve the pattern and
tell the robot what to do.
Uses
Most industrial robots are used in factories.
Some robots load, move, and
unload materials. Others are used on
assembly lines to help build things such
as cars and appliances.
Robots are especially useful because they
can do things that could be dangerous
for people. For example, they can be
sent deep underwater or into space.
Robots can also handle dangerous materials
such as radioactive waste or harmful
chemicals. They can even dispose of
bombs or do spy work for the military.
History
Writings from ancient Greece and China
tell of toys called automatons, which
were like robots. They were set in
motion by steam, air, water, or falling
weights. In the late 1700s and early
1800s complex automatons could play
music or write with a pen on paper.
During this time people also built
machines to help do certain kinds of
work. Modern robots only came about
Sony Corporation built a robot
that can throw a baseball.
74 Robot BRITANNICA STUDENT ENCYCLOPEDIA
after computers were invented.With
computers, people could program robots
to do tasks on their own.
Robots in Science Fiction
Robots often appear in science fiction,
or stories set in the future or in another
world. Robots in science-fiction books,
television shows, and movies can often
think, listen, talk, and walk easily on
two legs. Science-fiction robots that look
exactly like humans are known as
androids. Although real robots are
becoming more complex, they still are
not like these imagined robots.
#More to explore
Computer • Machine • Science Fiction
Rock
Rock, or stone, is a hard material made
up of one or more minerals. Rock makes
up the outer layer of Earth, called the
crust. The lower parts of this layer are
solid rock, or bedrock. Broken bits of
rock lie on top. The tiniest bits of rock
make up sand and soil. Underneath
Earth’s crust is a layer of melted rock,
called magma.
Types of Rock
There are three types of rock: igneous,
sedimentary, and metamorphic. These
names describe how each type of rock
was formed.
Igneous rock is hardened magma.
Magma may escape through cracks in
Earth’s crust. It may also come to
Earth’s surface when a volcano erupts.
As the escaped magma cools, it hardens
into solid rock. Granite and basalt are
examples of igneous rock.
Wave Rock in Australia is a formation of
granite, an igneous rock. The colored
bands are not layers but stains.
Devils Postpile in California is a
formation of basalt, an igneous
rock. Lava slowly hardened to
create the columns.
BRITANNICA STUDENT ENCYCLOPEDIA Rock 75
Sedimentary rock may form from pieces
of other rock. In a process called erosion,
wind and water slowly break rock
into tiny pieces.Water washes the pieces
into rivers. They settle along the river
bottom in soft, loose layers called sediment.
Over millions of years the sediment
builds up, hardens, and becomes
solid rock. Sandstone is a sedimentary
rock that forms in this way. Sedimentary
rock also may form from the remains of
dead animals or plants. Limestone is a
sedimentary rock that is made up of the
shells and stony skeletons of certain
kinds of living things.
Metamorphic rock forms from old igneous
or sedimentary rock. Several forces
can change old rock into new metamorphic
rock. Great heat and pressure inside
Earth’s crust can shape old rock into
metamorphic rock.Water can dissolve
minerals in old rock or carry new minerals
into it to form metamorphic rock.
The heat of magma can also change old
rock into metamorphic rock. Marble
