– Notes & Focus Questions
Directions: Use pages 43—52 in the
Introduction to Physical Science textbook and the following
information to answer the focus questions over Newton’s Laws of
While many scientists and philosophers like Aristotle or Galileo tried to
observe and discuss how objects move on Earth, Sir Isaac Newton
(1642—1727) was the first scientist to formulate a set of laws or
rules to summarize how all objects move on Earth and in the universe.
Newton came up with three laws that are still used today to help
scientists understand motion.
to fully understand Newton’s Three Laws of Motion, we must review two
important terms—motion and force. Motion happens when an object
changes position. The word force is much more difficult to understand
because it has meanings in English that are different from its
meanings in science. In the movie, Star Wars, the phrase “may the
force be with you” is used often. This Star Wars phrase represents
just one of the many definitions for the word force in English;
however, scientists think about forces in a different way. A force (in
science) is often defined as a push or pull on an object that can
produce motion. Another way to think about a force is as an
interaction between two objects involving a push or a pull. These
definitions indicate that in order to have a force, two objects must
be present—one object being pushed and another object doing the
pushing. The unit of force is a Newton, named for Sir Isaac Newton who
spent much of his life dedicated to analyzing force and motion.
Newton’s First Law of Motion states that an object will remain at rest
or in uniform motion unless an outside (unbalanced) force acts on the
object. This simply means that all objects have the tendency to resist
changes in motion. For example, a picture frame will hang on the wall
and not move unless another object comes along and forces (pushes or
pulls) it causing it to move. Newton’s First Law of Motion is also
known as the Law of Inertia. The property of an object that causes it
to resist changes in motion is called inertia. Therefore, objects at
rest and not moving will remain at rest and not moving. Inertia also
indicates the objects want to remain in uniform motion in a straight
line. This means objects tend to want to resist changes in speed or
direction. For example, when a car is turning a corner, a driver’s
body is usually thrown outward causing him/her to shift in their seat.
This shift of the body outward is due to inertia. When you enter a
turn in a car, the driver’s body inside the car wants to remain going
straight but the car turns so the body is thrown outward before
Newton also noticed
a special relationship between the mass and inertia of an object. He
found that the greater the mass of an object, the greater the inertia
of that object. Consequently, heavier objects are harder to move
because they have more inertia. Everyone has experienced this
relationship on a playground when pushing people on swings. An adult
is heavier and is harder to move than a lighter smaller child. This is
because the adult has a greater mass and more inertia than the child
Newton’s Second Law of Motion
states that the acceleration of an object is dependent upon the
force acting upon the object and the mass of the object. Newton’s
Second Law can be written as the equation:
F = m x a
m = mass (kg)
F = force (N)
a = acceleration (m/s/s)
This equation demonstrates the following two
important relationships between force, mass and acceleration:
- The greater the force on an object, the greater
the acceleration of an object.
Example: In baseball, if I hit a ball as hard as I can, the
ball goes accelerates more than if I was trying to bunt the ball.
- The greater the mass of an object, the smaller the acceleration.
Example: In baseball, if I hit a 5—pound
ball and a 1—pound ball with the same force,
the 5—pound ball would go slower than the 1—pound
ball because it has a greater mass.
Newton’s Third Law of
Motion states that for every action there is an equal and
opposite reaction. This means that when one object exerts a
force on a second object, the second object exerts the same amount
of force back on the first object but in the opposite direction. We
experience this law in many ways everyday. If a student were to jump
off of a desk onto the floor, their feet would sting. This is
because the student’s feet would exert a force on the ground but the
ground exerts a force back on the student’s feet causing their feet
FORCE UNIT: FOCUS QUESTIONS
Answer the following questions in complete sentences. If you need more
space, use an additional sheet of paper.
- See pages 43—52 in the Introduction to Physical
- Go to the website:
www.batesville.k12.in.us/physics (Go to Newton’s Laws)
- Define the word FORCE and state
what the unit is used for force.
- Define the word MOTION.
- What is the name of the scientist that formulated the Three Laws
- What does Newton’s First Law of Motion State? Give an example of
a way we see this law in our everyday lives.
- What is another name for Newton’s First Law of Motion? What does
the word INERTIA mean?
- What does Newton’s Second Law of Motion State? Why might this law
also be called “The Equation Law”?
- What is the relationship between force, mass and acceleration
implied by Newton’s Second Law of Motion? (State at least 2
- What does Newton’s Third Law of Motion State?
- A group of students are playing
kickball at the local elementary school. As they come out onto the
playground, they find two soccer balls lying on the grass perfectly
still. They notice during their game that if they kick the two balls
with the same force, the lighter ball has a greater acceleration
than the heavier ball. They also notice that as they kick the ball
around, it causes their toes to burn. Explain all three of Newton’s
Laws of Motion using this example.