Free fall and projectiles (as framed) - Physics 1 AP Study Notes
Overview
Have you ever dropped a ball, or watched a basketball player shoot a hoop? What about a dolphin leaping out of the water? All these everyday actions are perfect examples of **free fall** and **projectile motion**! Understanding how gravity pulls things down and how objects move through the air helps us design everything from roller coasters to space rockets. In this lesson, we'll explore how objects behave when they're only affected by gravity. We'll learn why a dropped feather falls slower than a dropped rock (and what happens if we remove the air!), and how to predict where a thrown ball will land. It's like being a detective for moving objects, using simple rules to solve mysteries of motion. So, get ready to unlock the secrets of things flying, falling, and soaring! This isn't just about physics; it's about understanding the world around you, from a tiny pebble to a massive cannonball.
What Is This? (The Simple Version)
Imagine you're at a super tall building and you drop a tiny pebble. What happens? It falls straight down, right? That's free fall! It means an object is only being pulled by gravity (the invisible force that pulls everything towards the Earth's center). We usually ignore air resistance for simplicity, like imagining the pebble is falling in a giant vacuum.
Now, what if you throw the pebble forward from that same building? It doesn't just fall straight down; it flies forward and falls down at the same time, making a curved path. This curved path is called projectile motion. Think of it like a basketball shot: the ball goes up, then forward, then down, all because of that initial push and gravity's constant pull.
Here's the cool part:
- Free fall is motion only in the up-and-down direction (vertical). Gravity makes things speed up as they fall.
- Projectile motion is motion in two directions at once: up-and-down (vertical) and side-to-side (horizontal). The horizontal motion is usually steady, while the vertical motion is affected by gravity, just like free fall.
Real-World Example
Let's think about a cannon firing a cannonball. This is a classic example of projectile motion.
- The Launch: When the cannon fires, it gives the cannonball a big push, sending it flying forward and usually a bit upwards. This is its initial velocity (starting speed and direction).
- The Journey: As the cannonball flies through the air, two things are happening at the same time:
- Horizontal Motion: It keeps moving forward at a pretty steady speed (if we ignore air pushing against it). There's no force pushing it faster forward once it leaves the cannon, and no force slowing it down horizontally (again, ignoring air resistance).
- Vertical Motion: Gravity is constantly pulling it downwards. So, even though it might be going up at first, gravity slows its upward climb, stops it at the very top of its path, and then pulls it faster and faster downwards.
- The Landing: Eventually, gravity wins, and the cannonball hits the ground. The path it took was a beautiful curve, a parabola, because of the combination of its steady forward motion and its gravity-affected up-and-down motion.
How It Works (Step by Step)
To understand how objects move in free fall or as projectiles, we break their motion into two separate, easier-to-handle parts: 1. **Separate the Directions:** Imagine a magical wall that splits the motion into a **horizontal** (sideways) part and a **vertical** (up-and-down) part. These two parts...
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Key Concepts
- Free Fall: The motion of an object when the only force acting on it is gravity.
- Projectile Motion: The motion of an object thrown or projected into the air, subject only to the force of gravity.
- Gravity: The invisible force that pulls objects towards the center of the Earth (or any other massive body).
- Acceleration due to Gravity (g): The rate at which gravity speeds up falling objects, approximately 9.8 m/sĀ² (or 10 m/sĀ²) downwards on Earth.
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Exam Tips
- āAlways draw a diagram! Sketching the path of the object and labeling initial velocity, angles, and displacements helps visualize the problem.
- āSeparate your work for horizontal (x) and vertical (y) components. Make two lists of knowns and unknowns, one for x and one for y.
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