#AP Physics C: Mechanics - Forces and Motion Study Guide 🚀

Welcome to your ultimate guide for mastering forces and motion! This guide is designed to be your go-to resource, especially the night before the exam. Let's get started!

#Overview

Time to dive into the heart of mechanics: forces! We'll explore how forces cause motion, stop motion, and everything in between. Get ready to understand Newton's laws, which are the foundation of classical mechanics. This unit is crucial for success in the rest of the course, so let's make sure you've got it down!

#Big Ideas

• Force Interactions: Forces define how objects or systems interact. Think of it as the push or pull between objects.
• Inertia: Why does coffee keep swirling after you stop stirring? That's inertia in action! ☕
• Net Force: Why doesn't a car move when you push it like a shopping cart? It's all about the net force.
• Action-Reaction: Why do you push backward to move forward on a skateboard? Newton's third law!
• Circular Motion: Why does the sun set in nearly the same place each day? Circular motion plays a role.

#Exam Impact

This unit accounts for 17-23% of the AP exam! That's a significant chunk, so let's make sure you're well-prepared. You should expect around 24 class periods (45 minutes each) to cover this material. The AP Classroom has 25 MCQs and 1 FRQ for practice.

#Newton's Laws of Motion: First and Second Law 🥏

Let's start with Newton's first two laws. These are the foundation for understanding how forces affect motion.

Newton's First Law of Motion: A body at rest will remain at rest unless an outside force acts on it, and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by a net external force.

Newton's Second Law of Motion: If an unbalanced force acts on a body, that body will experience acceleration (or deceleration).

#Free Body Diagrams (FBDs)

FBDs are your best friend in this unit! They help you visualize all the forces acting on an object. Remember to always consider direction and angles!

Here's a simple FBD example:

For the box at rest, we have:

• Gravitational Force (Weight): $F_g$ acting downwards.
• Normal Force: $F_n$ acting upwards.

Let's say the box has a mass of $m = 7.3$ kg. To find the force, use Newton's Second Law: $\Sigma F = ma$.

For the vertical forces ($y$-direction):

$\Sigma F_y = F_n - F_g$

Since the box is at rest, $a = 0$ m/s²:

$F_n - F_g = ma = (7.3)(0) = 0$

$F_n = F_g = mg = (7.3)(10) = 73$ N

So, the normal force and gravit...