The Speed and Force of a Projectile

Abstract

In our final reading selection from Galileo’s Dialogues, we find Salviati, Sagredo and Simplicio in the midst of a discussion of the motion of projectiles. By treating a projectile’s motion as a combination of uniform motion in the horizontal direction, and naturally accelerated motion in the vertical direction, they have discovered that its path forms one of Apollonius’s conic sections: the parabola. But can one determine the speed of the projectile at any and every point along its trajectory? How can it be calculated and what determines the force of impact? These are the questions to which they now turn.

For velocities, just as for intervals of time, there is need of a common standard which shall be understood and accepted by everyone, and which shall be the same for all.

—Galileo Galilei