14.1 Chapter 14: Newton’s Laws of Motion
Chapter Overview
According to Newton’s first law of motion, an object’s motion will not change unless it is acted upon by an unbalanced force. This tendency of an object to resist a change in motion is called inertia. Newton’s second law of motion states that the acceleration of an object equals the net force acting on the object divided by the object’s mass.
The acceleration of a mass due to gravity is measured by weight. Newton’s third law of motion states that every action has an equal and opposite reaction. During an action and reaction, momentum may be transferred from one mass to another, but overall momentum is conserved.
Online Resources
See the following Web sites for appropriate laboratory activities:
The lab at the following URL shows that resistance to motion depends on the mass of the body being accelerated rather than its weight.
• http://www.nuffieldfoundation.org/practical-physics/inertia-balance-or-wig-wag
In the lab at the following URL, students will verify Newton’s second law by subjecting a body to multiples of a force and then subjecting two bodies to the same force. Students will collect, analyze, and graph data collected during the lab.
• http://mypages.iit.edu/~smile/ph9527.html
The URL below offers six mini-labs on all three of Newton’s laws of motion.
• http://teachers.net/lessons/posts/661.html These Web sites may also be helpful:
You can teach Newton’s three laws of motion using part or all of the lesson plan at the following URL. The lesson includes background information and 11 class activities.
• http://www.clas.ufl.edu/users/ufhatch/NSF-PLANS/2-2_NEWTON.htm
Go to the URL below for a wealth of middle school materials on forces and motion, many of them dealing explicitly with Newton’s laws of motion. The materials include activities, labs, slideshows, online quizzes, study and review games, and interactive Web sites.
• http://www.science-class.net/Physics/force_motion.htm
14.1. Chapter 14: Newton’s Laws of Motion www.ck12.org
Pacing the Lessons
T
ABLE14.1:
Pacing the LessonsLesson Class Period(s) (60 min)
14.1 Newton’s First Law 1.5
14.2 Newton’s Second Law 2.0
14.3 Newton’s Third Law 2.5
14.2. Lesson 14.1 Newton’s First Law www.ck12.org
14.2 Lesson 14.1 Newton’s First Law
Key Concept
Newton’s first law of motion states that an object’s motion will not change unless an unbalanced force acts on the object. If the object is at rest, it will stay at rest. If the object is in motion, it will stay in motion. Inertia is the tendency of an object to resist a change in its motion. The inertia of an object depends on its mass. Objects with greater mass have greater inertia. To overcome inertia, an unbalanced force must be applied to an object.
Standards
• SCI.CA.8.PS.2.c
• MCR.6-8.SCI.10.4, 5
• NSES.5-8.B.2.2, 3
• AAAS.6-8.1.A.1; AAAS.6-8.4.F.3; AAAS.6-8.11.C.1
Lesson Objectives
• State Newton’s first law of motion.
• Define inertia, and explain its relationship to mass.
Lesson Vocabulary
• inertia:tendency of an object to resist a change in its motion
• Newton’s first law of motion:law stating that an object’s motion will not change unless an unbalanced force acts on the object
Teaching Strategies
Introducing the Lesson
Introduce inertia (and Newton’s first law) with one of the simple inertia demonstrations describe at the URL below.
Tell students they will understand what happened in the demonstration after they read this lesson. At the end of the lesson, call on students to explain what they observed in the demonstration.
• http://www.nuffieldfoundation.org/practical-physics/more-inertia-experiments
Demonstration
Have students participate in the demonstration described at the following URL. They will observe that mass resists changes in motion and that unbalanced forces produce changes in motion.
• http://www.nuffieldfoundation.org/practical-physics/inertia-low-friction-surface
Differentiated Instruction
Help focus students’ attention on the main points in the lesson by having them complete the following cloze sentences as they read. Tell them that each blank requires at least a few words to fill correctly. Sample answers are given in brackets below.
1. Newton’s first law of motion states that __________. [an object’s motion will not change unless an unbalanced force acts on the object]
2. Inertia is __________. [the tendency of an object to resist a change in its motion]
3. If an object is at rest, its inertia will __________. [keep it at rest]
4. If an object is moving, its inertia will __________. [keep it moving]
5. The inertia of an object depends on __________. [its mass]
Enrichment
Ask a few advanced students to help you place Newton’s laws of motion in a broader context. Have them do the activity described at the URL below. They will role-play interviews with three prominent scientists (Aristotle, Galileo, and Newton) who made major contributions to our understanding of motion. They will also identify how ideas about motion changed over time.
• http://www.middleschoolscience.com/motioninterview.htm
Science Inquiry
Have students do one or more of the five activities on Newton’s first law of motion at the following URL. The Web site provides Student Activity pages and Notes to Teachers. The activities will give students the opportunity to learn aspects of about the law in ways that are fun and interesting. The activities may be done individually or in groups. It is recommended that students create a logbook in which they take notes and track their findings from the activities.
• http://swift.sonoma.edu/education/newton/newton_1/html/newton1.html
Common Misconceptions
A misconception about motion that dates back to Aristotle is that an object keeps moving only if force is continuously applied to it. Help overcome this misconception with a simple demonstration. Slide a book across a table and have students watch as it slides to a rest position. Explain that the book stopped moving not because of the absence of force. Instead, it was the presence of force—the force of friction—that caused the book to stop moving. Add that in the absence of friction or some other force, the book would continue in motion with the same speed and direction forever (or at least to the end of the tabletop where the force of gravity would changes its motion).
14.2. Lesson 14.1 Newton’s First Law www.ck12.org
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in theCK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 14.1 Quiz inCK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
In this lesson, you read that the mass of an object determines its inertia. You also learned that an unbalanced force must be applied to an object to overcome its inertia, whether it is moving or at rest. An unbalanced force causes an object to accelerate.
• Predict how the mass of an object affects its acceleration when an unbalanced force is applied to it.
• How do you think the acceleration of an object is related to the strength of the unbalanced force acting on it?
14.3 Lesson 14.2 Newton’s Second Law
Key Concept
Newton’s second law of motion states that the acceleration of an object equals the net force acting on the object divided by the object’s mass. Weight is a measure of the force of gravity pulling on an object of a given mass. It equals the mass of the object (in kilograms) times the acceleration due to gravity (9.8 m/s2).
Standards
• SCI.CA.8.PS.2.e, f
• NSES.5-8.B.2.3
• AAAS.6-8.4.B.3; AAAS.6-8.4.F.3; AAAS.6-8.9.A.5; AAAS.6-8.11.C.3; AAAS.6-8.12.B.8, 9; AAAS.6-8.12.D.11
Lesson Objectives
• State Newton’s second law of motion.
• Identify the relationship between acceleration and weight.
Lesson Vocabulary
• Newton’s second law of motion:law stating that the acceleration of an object equals the net force acting on the object divided by the object’s mass
Teaching Strategies
Introducing the Lesson
With the help of a student volunteer, introduce students to Newton’s second law of motion with a simple demon- stration. While the class observes, ask the student to blow through a drinking straw held about an inch away from a ping-pong ball to start the ball rolling across a tabletop. Replace the ping-pong ball with a golf ball, and ask the student to repeat the procedure, blowing with about the same amount for force. Then ask the student to blow on each ball in succession with as much force as possible. Call on other students at random to describe what they observe and to identify the variables involved in the demonstration (force, mass, and acceleration). Tell the class they will learn how the variables are related when they read this lesson.
14.3. Lesson 14.2 Newton’s Second Law www.ck12.org Activity
Newton’s second law may be easier for students to understand if they do the interactive shopping cart activity at the URL below. They will see how acceleration is calculated, using different forces and masses, and also see a shopping cart actually accelerating at the calculated rates.
• http://www.classzone.com/books/ml_science_share/vis_sim/mfm05_pg50_newton/mfm05_pg50_newton.html
Differentiated Instruction
Students who need extra help with Newton’s second law of motion can read the tutorial and try the practice problems at the following URL. Solutions to the problems are provided.
• http://gbhsweb.glenbrook225.org/gbs/science/phys/Class/newtlaws/u2l3a.html Enrichment
Challenge interested students to think of a creative way to demonstrate Newton’s second law of motion to much younger students. Have them write a detailed description of the demonstration they would present. Then, if possible, arrange for the students to present their demonstration to an elementary-level class.
Science Inquiry
Have students do the guided inquiry activity described at the URL below. They will gather data on force, mass, and acceleration of a sliding mug and infer the relationships among the three factors from their data.
• http://www.education.com/reference/article/newton-law-motion2/?page=2 Real-World Connection
When you discuss Newton’s second law of motion, describe real-world scenarios that show how the acceleration of an object depends directly on the net force applied to the object and inversely on the object’s mass. Some examples you might use are listed below. Ask students to describe the resulting acceleration in each case.
• A book resting on a table (zero net force)
• Bunting a baseball (small force)
• Swinging at a baseball (large force)
• Pushing a bike with a flat tire (small mass)
• Pushing a car that has run out of gas (large mass)
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in theCK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 14.2 Quiz inCK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
Assume that a 5-kilogram skateboard and a 50-kilogram go-cart start rolling down a hill. Both are moving at the same speed. You and a friend want to stop then before they plunge into a pond at the bottom of the hill.
• Which will be harder to stop: the skateboard or the go-cart?
• Can you explain why?
14.4. Lesson 14.3 Newton’s Third Law www.ck12.org
14.4 Lesson 14.3 Newton’s Third Law
Key Concept
Newton’s third law of motion states that every action has an equal and opposite reaction. Momentum is a property of a moving object that makes it hard to stop. It equals the object’s mass times its velocity. When an action and reaction occur, momentum may be transferred from one object to another, but their combined momentum remains the same. This is the law of conservation of momentum.
Standards
• SCI.CA.8.PS.2.e, f
• NSES.5-8.B.2.3
• AAAS.6-8.4.F.3; AAAS.6-8.11.C.3; AAAS.6-8.12.B.8; AAAS.6-8.D.4, 6, 9, 11
Lesson Objectives
• State Newton’s third law of motion.
• Describe momentum and the conservation of momentum.
Lesson Vocabulary
• law of conservation of momentum: law stating that, when an action and reaction occur, the combined momentum of the objects remains the same
• momentum: property of a moving object that makes it hard to stop; equal to the object’s mass times its velocity
• Newton’s third law of motion:law stating that every action has an equal and opposite reaction
Teaching Strategies
Introducing the Lesson
Use two toy cars to demonstrate actions and reactions as a way to introduce lesson content. Push one toy car to start it rolling and aim it so that its front end collides with the back end of the other toy car, which is stationary. Students will observe that the moving car slows down after the collision, while the stationary car starts moving. Challenge students to explain their observations using terms such as force, velocity, and acceleration.
Building Science Skills
Challenge students to apply Newton’s third law to common activities such as jumping on a trampoline or hitting a golf ball with a golf club. In each case, ask students to identify the action and reaction forces and the objects to which the forces are applied. Also ask them to describe how the objects change in motion.
Demonstration
Use the animated collisions at the URL below to demonstrate conservation of momentum. Ask students to explain in words how momentum is conserved in each collision.
• http://www.physicsclassroom.com/mmedia/
Differentiated Instruction
Do a think-pair-share activity after students read the lesson first, ask students to think about the questions listed below. Then, divide the class into pairs, pairing students who need extra help with students who can provide it.
Finally, have partners work together to answer the questions (sample answers are given below in brackets).
1. What are actions and reactions? [equal and opposite forces]
2. What is an example of an action and reaction not described in the lesson? [Sample answer: hammering a nail into wood]
3. In your example, what is the action and what is the reaction? [action: the hammer hitting the nail; reaction:
the nail pushing into the wood]
4. How is momentum involved in your example? [Some of the momentum of the hammer is transferred to the nail.]
Enrichment
Ask a group of students to brainstorm a creative way to demonstrate how mass and velocity affect an object’s momentum. With your approval, have the students make a video of their demonstration to share with the class.
Science Inquiry
Have small groups of students discuss and try to solve the problems at the URL below (answers are provided). The problems require students to apply Newton’s third law of motion and the concept of momentum.
• http://www.physicsclassroom.com/class/momentum/u4l2a.cfm
Real-World Connection
Many sports provide real-world examples of Newton’s third law of motion. Have students watch the video below to see how Newton’s third law applies to football.
• http://www.nsf.gov/news/special_reports/football/newtonthirdlaw.jsp
14.4. Lesson 14.3 Newton’s Third Law www.ck12.org
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in theCK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 14.3 Quiz inCK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
In this chapter, you learned about forces and motions of solid objects, such as balls and cars. In the next chapter,
“Fluid Forces,” you will learn about forces in fluids, which include liquids and gases.
• How do fluids differ from solids?
• What might be examples of forces in fluids? For example, what force allows some objects to float in water?
C HAPTER
15 TE Fluid Forces
Chapter Outline
15.1 CHAPTER15: FLUIDFORCES