http://www.ck12.org Chapter 4. Motion and Forces
4.18 Projectile Motion
- Describe projectile motion and state when it occurs.
- Give examples of projectile motion.
The archer in the opening image is aiming his arrow a little bit above the bull’s eye of the target, rather than directly
at it. Why doesn’t he aim at the bull’s eye instead? The answer is projectile motion.
Combining Forces
When the archer releases the bowstring, the arrow will be flung forward toward the top of the target where she’s
aiming. But another force will also act on the arrow in a different direction. The other force is gravity, and it will
pull the arrow down toward Earth. The two forces combined will cause the arrow to move in the curved path shown
in theFigure4.32. This type of motion is calledprojectile motion. It occurs whenever an object curves down
toward the ground because it has both a horizontal force and the downward force of gravity acting on it.
Because of projectile motion, to hit the bull’s eye of a target with an arrow, you actually have to aim for a spot above
the bull’s eye. You can see in theFigure4.33 what happens if you aim at the bull’s eye instead of above it.
Another Example of Projectile Motion
You can probably think of other examples of projectile motion. One is shown in theFigure4.34. The cannon shoots
a ball straight ahead, giving it horizontal motion. At the same time, gravity pulls the ball down toward the ground.