1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Newton’s First Law Newton’s first law of motion states that an object at rest remains at rest and an object in motion maintains its velocity unless it experiences an unbalanced force. Objects tend to maintain their state of motion. Inertia is the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object. Section 1 Laws of Motion Chapter 11

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Newton’s First Law Section 1 Laws of Motion Chapter 11

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Newton’s First Law, continued Inertia is related to an object’s mass. Mass is a measure of inertia. Seat belts and car seats provide protection. Because of inertia, you slide toward the side of a car when the driver makes a sharp turn. When the car you are riding in comes to a stop, your seat belt and the friction between you and the seat stop your forward motion. Section 1 Laws of Motion Chapter 11

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mass and Inertia Section 1 Laws of Motion Chapter 11

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Newton’s Second Law Newton’s second law of motion states that the unbalanced force acting on an object equals the object’s mass times its acceleration. Force equals mass times acceleration. Force = mass  acceleration F = ma Force is measured in newtons (N). 1 N = 1 kg  1 m/s 2 Section 1 Laws of Motion Chapter 11

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Newton’s Second Law Section 1 Laws of Motion Chapter 11

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Newton’s Second Law Section 1 Laws of Motion Chapter 11

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Math Skills Newton’s Second Law Zookeepers lift a stretcher that holds a sedated lion. The total mass of the lion and stretcher is 175 kg, and the lion’s upward acceleration is 0.657 m/s 2. What is the unbalanced force necessary to produce this acceleration of the lion and the stretcher? 1. List the given and unknown values. Given: mass, m = 175 kg acceleration, a = 0.657 m/s 2 Unknown: force, F = ? N Section 1 Laws of Motion Chapter 11

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Math Skills, continued 2. Write the equation for Newton’s second law. force = mass  acceleration F = ma 3. Insert the known values into the equation, and solve. F = 175 kg  0.657 m/s 2 F = 115 kg  m/s 2 = 115 N Section 1 Laws of Motion Chapter 11

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Newton’s Second Law, continued Newton’s second law can also be stated as follows: The acceleration of an object is proportional to the net force on the object and inversely proportional to the object’s mass. Section 1 Laws of Motion Chapter 11