Newton's Laws – Notes
 Force & Motion

### Newton's Laws – 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 Motion.

Background Information:
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.

In order 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 correcting itself.

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 does.

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 Where m = mass (kg) F = force (N) a = acceleration (m/s/s)

This equation demonstrates the following two important relationships between force, mass and acceleration:

1. 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.
2. The greater the mass of an object, the smaller the acceleration.
Example: In baseball, if I hit a 5pound ball and a 1pound ball with the same force, the 5pound ball would go slower than the 1pound 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 to sting.

FORCE UNIT: FOCUS QUESTIONS

Directions: Answer the following questions in complete sentences. If you need more space, use an additional sheet of paper.

1. See pages 43—52 in the Introduction to Physical Science textbook.
2. Go to the website: www.batesville.k12.in.us/physics (Go to Newton’s Laws)

Questions:

1. Define the word FORCE and state what the unit is used for force.
2. Define the word MOTION.
3. What is the name of the scientist that formulated the Three Laws of Motion?
4. What does Newton’s First Law of Motion State? Give an example of a way we see this law in our everyday lives.
5. What is another name for Newton’s First Law of Motion? What does the word INERTIA mean?
6. What does Newton’s Second Law of Motion State? Why might this law also be called “The Equation Law”?
7. What is the relationship between force, mass and acceleration implied by Newton’s Second Law of Motion? (State at least 2 relationships)
8. What does Newton’s Third Law of Motion State?
9. 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.

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