Counterimpetus

Counterimpetus is a concept originating from Aristotelian physics that attempts to explain the motion of projectiles. In Aristotelian physics, projectiles are not seen as simply continuing to move due to inertia. Instead, it was theorized that the initial impetus imparted by the thrower or launcher does not sustain the motion indefinitely.

According to this theory, the impetus is gradually consumed or dissipated. For a projectile to continue moving after it leaves the source of propulsion, it requires a continuous impartation of force. This is where counterimpetus comes in. It is the idea that some opposing force, often attributed to the surrounding air, acts against the projectile's motion. This opposing force, the counterimpetus, is what gradually diminishes the projectile's speed and eventually causes it to fall.

Aristotle himself did not use the term "counterimpetus," but his followers and later commentators developed this idea to address the observed motion of objects. They proposed that the air, in some way, pushes back against the projectile, slowing it down. This explanation was contrasted with the idea that the air might actually assist the projectile's motion, as some interpretations of Aristotle suggested. The concept of counterimpetus was eventually superseded by Newtonian physics, which explains projectile motion through inertia, gravity, and air resistance as distinct forces.