Topic 1.3: Free Fall

Name: _______________________________ Date: _______________

Before We Start: Yesterday's Recap

Yesterday we learned the 4 kinematic equations. Without looking back: what are the 5 variables, and which one does each equation leave out?

Today's New Concepts

AP CED Alignment: Unit 1, Topics 1.2/1.3

Free Fall

• Motion under gravity ALONE — no air resistance
• Every object accelerates downward at the same rate: $g \approx 9.8\text{ m/s}^2$, regardless of mass
• A hammer and a feather fall at the same rate on the Moon (no air) but not on Earth (air resistance affects the feather far more)

Sign Convention (pick one and stick with it!)

• Common choice: up = positive, so $g = -9.8\text{ m/s}^2$ (gravity pulls down)
• Use this same sign for a in all 4 kinematic equations from Topic 1.2, Session 5 — nothing else changes

Worked Example — Thrown Straight Up

• At the very top of the path, velocity = 0 for an instant — but acceleration is still −9.8 m/s² the ENTIRE time, including at the top
• Time going up = time coming down (the motion is symmetric in time when the object returns to its starting height)

Common Mistake

Students often think acceleration is zero at the top of a toss because velocity is zero there. Velocity and acceleration are different quantities — gravity never turns off, so acceleration is constant throughout the whole flight.

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Keep This Sheet!

These sheets build into your semester study guide. Keep them in order in a binder or folder — you'll want to flip back through them before quizzes, unit tests, and when AP exam review starts in the spring.