The cannonball falls the same amount of distance as it did when it was merely dropped from rest (refer to diagram below). Furthermore, the force of gravity will act upon the cannonball to cause the same vertical motion as before - a downward acceleration. If our thought experiment continues and we project the cannonball horizontally in the presence of gravity, then the cannonball would maintain the same horizontal motion as before - a constant horizontal velocity. This is consistent with our conception of free-falling objects accelerating at a rate known as the acceleration of gravity. And furthermore, if merely dropped from rest in the presence of gravity, the cannonball would accelerate downward, gaining speed at a rate of 9.8 m/s every second. This is consistent with the law of inertia. In the absence of gravity, the cannonball would continue its horizontal motion at a constant velocity. Consider a cannonball projected horizontally by a cannon from the top of a very high cliff. Let's return to our thought experiment from earlier in this lesson. The goal of this part of the lesson is to discuss the horizontal and vertical components of a projectile's motion specific attention will be given to the presence/absence of forces, accelerations, and velocity. And since perpendicular components of motion are independent of each other, these two components of motion can (and must) be discussed separately. There are the two components of the projectile's motion - horizontal and vertical motion. That is, as they move upward or downward they are also moving horizontally. Many projectiles not only undergo a vertical motion, but also undergo a horizontal motion. As discussed earlier in this lesson, a projectile is an object upon which the only force acting is gravity.

Horizontal motion