a score. The offense can move the ball
either by running with it or by throwing,
or passing, it. The different types of
running or throwing tactics that the
offense uses are called plays. The offense
designs plays to move forward by overpowering
or fooling the defense. The
offensive player called the quarterback
begins most plays. The quarterback usually
hands or passes the ball to a teammate.
The defense tries to prevent the other
team from scoring. Defensive players
can tackle the quarterback or any other
player who has the ball. They can also
catch a pass that the quarterback meant
to throw to a teammate. This is called an
interception. The team that makes the
interception then switches to offense.
The offense has four tries, called downs,
to move the ball at least 10 yards. If the
offense fails to do this, the other team
gets the ball. If the offense does move
the ball 10 yards or more, it gets another
four downs. This continues until the
offense scores, the defense takes away
the ball, or time runs out.
The offense can score touchdowns or
field goals. Running or passing the ball
across the goal line scores a touchdown.
A touchdown is worth six points. After a
touchdown the scoring team has a
chance to earn extra points. Kicking the
ball between the goalposts is worth one
point. Getting the ball into the end zone
An American professional football field is almost the same as a college football field.
American
football is also
called gridiron
football.
BRITANNICA STUDENT ENCYCLOPEDIA Football 49
by running or passing earns two points.
When the offense does not score a
touchdown, it can score three points by
kicking the ball between the goalposts.
This is a field goal.
Sometimes the defense scores, too. If an
offensive player drops the ball, a defensive
player can pick it up and carry it for
a touchdown. Also, a defensive player
can run with the ball after intercepting a
pass. The defense scores two points by
trapping the offense in its own end zone.
This is called a safety.
History
Football started in the late 1800s in the
United States as a college sport. Princeton
and Rutgers played the first college
football game in 1869. This game was
similar to soccer. In 1871 students at
Harvard University invented their own
game. It combined soccer and the
English game called rugby. In 1876 representatives
from Harvard, Princeton,
Yale, and Columbia universities wrote a
set of football rules based on rugby.
Walter Camp, a coach at Yale, helped to
separate the game of American football
from rugby. Camp introduced the
11-man team and the line of scrimmage.
He also began the system of downs.
The first professional football game was
played in 1895. In 1920 professional
football teams formed the organization
that would later be called the National
Football League (NFL). In 1970 the
rival American Football League became
part of the NFL. Since 1967 the two
best teams at the end of each season
have competed for the Super Bowl
championship. This game is one of the
most watched shows on television.
#More to explore
Rugby • Soccer
Force
A force is a push or a pull on an object.
A force happens when two objects
interact—that is, when one object does
something to the other object. When
the interaction stops, the force stops,
too.
Contact Forces
and Field Forces
There are two types of forces: contact
forces and field forces. Contact forces
happen when objects touch each other.
For example, contact forces happen
when a person kicks a ball or pulls a
wagon. Other examples of contact forces
are sandpaper rubbing on a piece of
wood and wind blowing against a moving
car.
Touch football
and flag football
are versions
of
football that
are often
played in U.S.
elementary
schools. They
are not as
rough as
tackle football.
Each side in a tug-of-war game uses force
to try to pull down the other side.
50 Force BRITANNICA STUDENT ENCYCLOPEDIA
Field forces happen when two objects
interact without touching each other.
Field forces can create a push or a pull
even at a distance. Gravity is a field
force. When an apple falls from a tree,
the force of gravity pulls the apple
toward the ground. Another field force
is magnetism. Paper clips stick to a magnet
because its magnetic force is pulling
on the paper clips.
Measuring Force
Most scientists measure force using a
unit called the newton. Newtons measure
the force needed to accelerate, or
speed up, objects. Force may also be
measured in pounds.
Forces and the Laws of Motion
In the late 1600s, the English scientist
Isaac Newton came up with three laws
that deal with forces and motion. The
first law says that the motion of an
object will not change unless a force
pushes or pulls it. The second law says
that a force on an object will make the
object speed up in the same direction as
the force. Also, a strong force will make
the object speed up faster than a weak
force on the same object. The third law
says that whenever a force pushes on an
object, the object pushes back with an
equal and opposite force.
..More to explore
Gravity • Magnet and Magnetism
• Motion
Ford, Gerald R.
Gerald Ford was the 38th president of
