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How does air resistance change the motion of a falling object?

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Title page of Isaac Newton's Philosophiae Naturalis Principia Mathematica, 1687, featuring large Latin text and publication details in a bordered layout. — Newton’s laws of motion The title page of Isaac Newton's *Philosophiae Naturalis Principia Mathematica* (1687; *Mathematical Principles of Natural Philosophy*), the work in which the physicist introduced his three laws of motion.

When an object falls through a fluid like air, it is subject to air resistance, which acts as an upward force opposing the downward pull of gravity. While objects in a vacuum fall with constant acceleration, air resistance modifies this motion by increasing as the object's speed increases.12

As a falling object accelerates, the force of air resistance grows until it equals the object's weight. At this point, the net force on the object becomes zero, and its acceleration ceases. The object then maintains a constant speed known as terminal velocity.1

The specific behavior of this resistance depends on the object's properties and the medium. For small particles, Stokes’s law provides a mathematical description of the drag force, showing how factors like particle size and fluid viscosity influence the velocity of the fall. In contrast to the idealized model of freefall where all bodies fall with the same constant acceleration, air resistance ensures that the motion of real-world objects is limited by the balance between gravitational and resistive forces.312