Download Getting to Know: Newton`s Laws

Getting to Know: Newton’s Laws
You might think that baseball is just about throwing
a ball, swinging a bat, and running the bases.
However, baseball is about far more than that—it is
all about forces and motion.
When the bat hits the ball, the ball changes
direction.
When a pitcher pitches the ball, a force is applied
to the ball, and the ball moves through the air as
a result of this force. The batter swings, and if the
bat makes contact with the ball, the ball changes
direction. At the moment the ball is hit, the bat
applies a force to the ball, but the ball also applies
force to the bat. If you’ve ever hit a ball with a bat,
you’ve felt the impact of that force.
Other sports
such as soccer
involve forces and motion as well. If a soccer player kicks a
ball that is resting motionless on the field, the ball moves.
If another player jumps up and heads the ball, the player’s
head exerts a force on the ball. The result of this new force
is a change in motion.
How can forces and motion be explained
scientifically?
To understand the causes of forces and motion, we have to discuss Isaac Newton and his three laws of motion. Isaac Newton was a scientist and mathematician who lived in the
1700s. You might have heard the famous story of how he was inspired to study gravity and other forces when he saw
an apple fall from a tree. There is some truth in this story,
although it has become somewhat exaggerated over time.
Newton carefully investigated the forces that cause motion,
including gravity. His study led him to formulate three statements that explain the relationship between forces and motion. We now refer to these statements as Newton’s
three laws of motion. These laws describe the behavior of
objects in response to the forces that act on them. Concept: Newton’s Laws
Getting to Know
www.discoveryeducation.com
1
The soccer ball applies a force
to the player’s head, and the
player’s head applies a force to
the soccer ball.
© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.
What are Newton’s three laws of motion?
Newton’s first law, sometimes called the law of inertia, states
that objects in motion tend to stay in motion, and objects at
rest tend to stay at rest. This means that a force is required to
cause an object at rest to move. This explains why a force is
required to move a soccer ball sitting motionless on a field.
Newton’s first law also explains why a force is required to
cause an object in motion to stop. In other words, it explains
how forces can prevent a soccer ball from rolling on forever.
Misconception 1: If an object is in motion, a force
acts on it to keep it going.
Newton’s first law of motion states that a force is
not needed to keep an object in motion. An object
sliding across a table doesn’t come to rest because of
the absence of a force. The object stops because of
friction, a force that works against motion.
Why do the apples always
fall straight to the ground?
Newton’s second law states that a force applied to an object will cause that object to accelerate, or change its speed or direction. In the baseball game we talked about, the baseball bat applied a force to the ball, which changed the ball’s speed and direction. Newton’s second law also explains how acceleration is related to an object’s mass. If an object’s mass increases, more force is required to accelerate the object. That is why it takes more force to move a bowling ball than it takes to move a beach ball. Newton’s third law states that for every action, there is an equal and opposite reaction. This explains why rockets accelerate—a rocket’s engines release hot gases that exert a very strong downward force. The rocket reacts by moving in the opposite direction: upward. Altogether, Newton’s three laws can describe and explain any type of motion that results from forces acting on an object. You will learn more about Newton’s laws of motion in this lesson!
Misconception 2: An object in motion will naturally slow down even if a force does
not oppose its motion.
That is not true. Newton’s first law states that an object at rest tends to stay at rest,
and an object in motion tends to stay in motion with the same speed and in the same
direction unless acted on by another force. If a force does not oppose an object’s
motion, the object will continue moving in the same speed and direction indefinitely.
Concept: Newton’s Laws
Getting to Know
www.discoveryeducation.com
2
© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.