The Influence of Air Resistance
Objects fall at different rates in Earth's atmosphere primarily due to air resistance, also known as drag. This force opposes an object's motion through the air, acting in the opposite direction of its velocity. The magnitude of air resistance depends on several factors, including the object's shape, size, surface area, and its speed, as well as the density of the air.
Factors Affecting Air Resistance
A larger surface area, a less aerodynamic shape, and a higher speed all contribute to greater air resistance. For instance, a flat sheet of paper experiences significantly more air resistance than a crumpled ball of the same paper, even though they have the same mass, because its larger surface area interacts more extensively with air particles.
Terminal Velocity Explained
As an object falls, its speed increases, and so does the air resistance it encounters. Eventually, the upward force of air resistance can become equal in magnitude to the downward force of gravity. At this point, the net force on the object becomes zero, and it stops accelerating, continuing to fall at a constant maximum speed known as its terminal velocity.
Contrast with a Vacuum
In a vacuum, where there is no air, there is no air resistance to impede an object's fall. Consequently, all objects, regardless of their mass, shape, or size, fall at the same rate due to the constant acceleration of gravity. This phenomenon is often demonstrated with a feather and a hammer falling simultaneously in an evacuated chamber, reaching the ground at the exact same time.