1. Unit 15 Lesson 4 What Are Newton’s Laws? Copyright © Houghton Mifflin Harcourt Publishing Company

2. Unit 15 Lesson 4 What Are Newton’s Laws? Copyright © Houghton Mifflin Harcourt Publishing Company

3. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s First Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company In the 1600s, Isaac Newton published a book about how objects move in the physical world. Newton summed up his ideas in three rules, or laws.

4. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s First Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company Newton’s first law of motion states that no acceleration, or change in motion, can happen without an unbalanced force, or push or pull. In other words, objects at rest don’t move unless an unbalanced force acts on them. Objects in motion don’t slow down, speed up, stop, or turn unless a force makes them do so.

5. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s First Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company Newton’s first law describes inertia, or the tendency of objects to resist a change in motion.inertia For example, when a car makes a sudden turn, your body pulls to the other side of the car.

6. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s First Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company

7. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s First Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company

8. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Second Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company Newton’s second law of motion states that an object’s acceleration depends on two factors: the amount of force applied to the object and its mass.

9. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Second Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company The mass of an object affects how, or if, the object moves when a force is applied to it. Newton’s second law explains why you must use more force to move an object with a greater mass. This law can be written as an equation: Force = mass x acceleration

10. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Second Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company

11. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Second Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company

12. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Second Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company

13. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Third Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company Newton’s third law of motion states that whenever one object applies force to another, the second object applies an equal, opposite force to the first object. In other words, this law says that forces always act in pairs.

14. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Third Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company Sometimes scientists use the terms action force and reaction force to refer to a pair of forces. In other words, the two forces described above are equal in size and opposite in direction. For example, when leaning against a wall, your body applies force to the wall. The wall doesn’t move because it applies the same amount of force to you.

15. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Third Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company

16. Unit 15 Lesson 4 What Are Newton’s Laws? Newton’s Third Law of Motion Copyright © Houghton Mifflin Harcourt Publishing Company

17. Unit 15 Lesson 4 What Are Newton’s Laws? Motion in Space Copyright © Houghton Mifflin Harcourt Publishing Company Astronauts in orbit appear to be weightless. To understand motion of objects in space, it’s important to remember the difference between weight and mass. Mass refers to how much matter is in an object. Weight refers to how much force is applied to an object by gravity.

18. Unit 15 Lesson 4 What Are Newton’s Laws? Motion in Space Copyright © Houghton Mifflin Harcourt Publishing Company Newton’s laws of motion apply to objects in space, because the laws involve mass, not weight. The mass of an object is the same on Earth and in space. An object’s weight can change because weight is related to the force of gravity at a particular location.

19. Unit 15 Lesson 4 What Are Newton’s Laws? Motion in Space Copyright © Houghton Mifflin Harcourt Publishing Company Astronauts feel and look weightless because of microgravity. Microgravity occurs because Earth’s gravity causes the space station to fall toward Earth at a constant rate. Everything inside the space station falls at the same rate.

20. Unit 15 Lesson 4 What Are Newton’s Laws? Motion in Space Copyright © Houghton Mifflin Harcourt Publishing Company

21. Unit 15 Lesson 4 What Are Newton’s Laws? Motion in Space Copyright © Houghton Mifflin Harcourt Publishing Company Because astronauts are also in free fall, they appear to float.

22. Unit 15 Lesson 4 What Are Newton’s Laws? Motion in Space Copyright © Houghton Mifflin Harcourt Publishing Company

23. Unit 15 Lesson 4 What Are Newton’s Laws? Copyright © Houghton Mifflin Harcourt Publishing Company

24. Unit 15 Lesson 4 What Are Newton’s Laws? Copyright © Houghton Mifflin Harcourt Publishing Company