Unit I: Acceleration
The Science of Changing Motion.
This is the second chapter of the Physics curriculum. It builds on our understanding of velocity.
← Go back to Chapter 1: Introduction to Kinematics.
The Problem: Speeding Up and Slowing Down
In the last chapter, we learned to describe motion with constant velocity. But in the real world, things rarely move at a steady speed. Cars speed up, balls slow down, and objects fall from the sky faster and faster. How do we describe this *change* in velocity?
The answer is acceleration. It's not just about "going fast"—it's about how *quickly* you're changing how fast you're going.
Acceleration is a vector, just like velocity. This means it has direction. A positive acceleration means you're speeding up in the positive direction. A negative acceleration (also called deceleration) can mean you're slowing down, OR it can mean you're speeding up in the negative direction!
Interactive Acceleration Simulator
This is where it all comes together. Use the sliders to set an initial velocity and a constant acceleration, then press "Play" to see what happens. Pay close attention to the velocity vector (the arrow) on the ball.
The "Aha!" Moment
Try these scenarios to build your intuition:
- Positive Velocity, Positive Acceleration: The ball speeds up to the right. The velocity arrow gets longer.
- Positive Velocity, Negative Acceleration: The ball slows down, stops, and then starts speeding up to the left! This is like throwing a ball up in the air.
- Negative Velocity, Negative Acceleration: The ball speeds up to the left. The velocity arrow gets longer in the negative direction.
The key takeaway is that acceleration is the "pull" on the velocity. A positive acceleration always pulls the velocity value towards the positive, and a negative acceleration pulls it towards the negative.
You Understand Changing Motion. What's Next?
You've now learned how to describe motion that isn't constant. The next step is to apply this to the most common form of acceleration on Earth: gravity.