Topic 1.5: Intro to Projectile Motion

Name: _______________________________ Date: _______________

Before We Start: Yesterday's Recap

Yesterday we learned free fall. Without looking back: is acceleration zero at the top of a ball's toss upward? Why or why not?

Today's New Concepts

AP CED Alignment: Unit 1, Topic 1.5

The Independence Principle

Horizontal motion and vertical motion happen COMPLETELY independently of each other
Horizontal: no acceleration (ignoring air resistance) → constant velocity → $x = v_xt$
Vertical: free fall, exactly like Topic 1.3, Session 6 (Free Fall) → $\Delta y = \tfrac{1}{2}at^2$ (starting vertical velocity = 0 for a horizontally-launched projectile)

Solving Strategy: Vertical First, Then Horizontal

Solve the VERTICAL motion first to find the time of flight (horizontal velocity is irrelevant to this step)
Plug that time into the HORIZONTAL equation to find the range (distance traveled sideways)

Worked Example

A ball rolls off a table 1.225 m high at 4 m/s horizontal.

Vertical: $1.225 = \tfrac{1}{2}(9.8)t^2 \rightarrow t = 0.5\text{ s}$
Horizontal: $x = 4(0.5) = 2\text{ m}$

Key Takeaway

Two identical balls — one dropped straight down, one launched horizontally off the same height at the same instant — hit the ground at the EXACT same time. The horizontal speed only changes where the ball lands, not when.

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.