4.1. The Big Idea http://www.ck12.org
4.1 The Big Idea
In this chapter, we aim to understand and explain the parabolic motion of a thrown object, known as projectile
motion. We can break down any initial velocity vector into its vertical and horizontal components. Motion in one
direction is unrelated to motion in perpendicular directions, so we can treat the individual components as separate
one-dimensional motion problems using all the equations from the last chapter. Once the object has been thrown, the
only acceleration is from gravity, in the vertical direction. The horizontal component of velocity remains unchanged
(ignoring air resistance) throughout the flight.
MEDIA
Click image to the left for more content.Key Equations
Vertical Direction
+y =Upward
y(t) =y 0 +v 0 yt−^12 gt^2
vy(t) =v 0 y−gt
vy^2 =v 0 y^2 − 2 g(∆y)
ay=−g =− 9 .8m/s^2Horizontal Direction
x(t) =x 0 +v 0 xt
vx(t) =v 0 x
ax = 0Note:the initial velocityv 0 can be separated intov 0 x=v 0 cosθandv 0 y=v 0 sinθ, whereθis the angle between the
velocity vector and the horizontal.
Key Concepts
- In projectile motion, the horizontal displacement of an object from its starting point is called itsrange.
- Vertical speed is zero only at the highest point of a thrown object’s flight.