# Chapter 4: Newton's Laws

We have just finished our study of kinematics. In kinematics we did not care **why** an object was moving. We are now going to explain why objects move or do not move. We do so by using the concept of force. In this chapter we consider the basic techniques of free-body diagrams, the normal force, and the forces of weight and tension.

# Table of Contents

## Illustrations

- Illustration 4.1: Newton's First Law and Reference Frames.
- Illustration 4.2: Free-Body Diagrams.
- Illustration 4.3: Newton's Second Law and Force.
- Illustration 4.4: Mass on an Incline.
- Illustration 4.5: Pull Your Wagons.
- Illustration 4.6: Newton's Third Law, Contact Forces.

## Explorations

- Exploration 4.1: Vectors for a Box on an Incline.
- Exploration 4.2: Change the Two Forces Applied.
- Exploration 4.3: Change the Force Applied to Get to the Goal.
- Exploration 4.4: Set the Force on a Hockey Puck.
- Exploration 4.5: Space Probe with Multiple Engines.
- Exploration 4.6: Putted Golf Ball Breaks Toward the Hole.
- Exploration 4.7: Atwood's Machine.
- Exploration 4.8: Enter a Formula for the Force Applied.

## Problems

- Problem 4.1: Which is the correct free-body diagram?
- Problem 4.2: Interpret the free-body diagram.
- Problem 4.3: Pull your little red wagon.
- Problem 4.4: Pull your little red wagon.
- Problem 4.5: A buoy is dropped into a lake.
- Problem 4.6: Putted golf ball.
- Problem 4.7: A ball constrained to move on a rod.
- Problem 4.8: Take a ride in an elevator.
- Problem 4.9: Rank the accelerations and tensions.
- Problem 4.10: Hoisted boxes.
- Problem 4.11: Modified Atwood's machine.
- Problem 4.12: A truck and car collision.
- Problem 4.13: Does the force obey Newton's third law?