#AP Physics 1: Newton's Third Law - Your Ultimate Guide 🚀

Hey there, future physics pro! Let's break down Newton's Third Law and get you feeling super confident for the exam. This guide is designed to be your go-to resource, especially the night before the test. Let's make sure everything clicks!

Newton's Third Law is a cornerstone of mechanics, and understanding it is crucial for success in AP Physics 1. It's not just a formula; it's a concept that explains how forces work in pairs. You'll see it everywhere, from simple object interactions to complex systems.

#1. Newton's Third Law: Action-Reaction Pairs 🤝

#1.1. The Core Principle

• Newton's Third Law: For every action, there is an equal and opposite reaction. This means forces always come in pairs.
• Think of it like a high-five: your hand exerts a force on your friend's, and their hand exerts an equal force back on yours. ✋
• Key Point: Forces always act on different objects. This is why they don't cancel each other out!

#1.2. Mathematical Representation

• The formula: $$\vec{F}_{A \text{ on } B} = -\vec{F}_{B \text{ on } A}$$
• This means the force of A on B is equal in magnitude but opposite in direction to the force of B on A.

#1.3. Action-Reaction Examples

• Book on a Table: The book pushes down on the table (action), and the table pushes up on the book (reaction).
• Jumping off a Boat: You push the boat backward (action), and the boat pushes you forward (reaction).

#2. Internal Forces and Center of Mass ⚖️

#2.1. Internal vs. External Forces

• Internal Forces: Forces between objects within a system. These always come in action-reaction pairs.
• External Forces: Forces exerted on the system by objects outside the system. These can...