Foundations of Motion and Kinematics
TL;DR
This section introduces you to how we describe motion, including speed, acceleration, and the forces that cause them. You'll learn to interpret motion graphs and understand simple machines. Finally, we'll touch on real-world applications like flight and vehicle stopping distance.
1. The Mental Model
Imagine an apple falling from a tree; it speeds up due to gravity. The way we describe this speeding up (acceleration) and the reason it happens (forces) are the basic ideas here. You'll learn to quantify and predict this motion.
2. The Core Material
Distance, Time, and Speed
When something moves, it covers a distance over a period of time. Speed is simply how fast something is moving, calculated as distance divided by time.
For example, if you travel 100 meters in 10 seconds, your speed is 100 meters / 10 seconds = 10 meters per second (m/s).
Distance-Time Graphs
These graphs show you an object's distance from a starting point over time.
* A flat horizontal line means the object isn't moving (distance isn't changing).
* A straight, upward-sloping line means constant speed. A steeper slope means a faster constant speed.
* A curved line means the speed is changing (the object is accelerating or decelerating).
Velocity-Time Graphs
These graphs show an object's velocity (speed in a specific direction) over time.
* A flat horizontal line means constant velocity (no acceleration).
* A straight, upward-sloping line means constant positive acceleration (speeding up).
* A straight, downward-sloping line means constant negative acceleration (slowing down).
* The area under a velocity-time graph gives you the total distance traveled.
Calculating Acceleration
Acceleration is the rate at which velocity changes. If your velocity changes, you're accelerating. It's calculated as the change in velocity divided by the time it took for that change.
Acceleration = (Final Velocity - Initial Velocity) / Time
Its unit is usually meters per second squared (m/s²). If you speed up from 0 m/s to 10 m/s in 2 seconds, your acceleration is (10 - 0) / 2 = 5 m/s².
Forces and Newton's Laws
A force is a push or a pull. Forces cause objects to accelerate, change direction, or deform.
* Newton's First Law (Law of Inertia): An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced