When an object falls, it moves downward due to gravity. The speed at which it falls is determined by an interplay of forces. Understanding this science clarifies why different items drop at varying rates in our atmosphere.
The Fundamental Force of Gravity
Gravity is the force that pulls objects towards the center of the Earth. This force causes objects to accelerate, meaning their speed increases as they fall. In a theoretical environment without air, all objects, regardless of mass, fall with the same constant acceleration. This acceleration, ‘g’, is approximately 9.8 meters per second squared (m/s²) or 32 feet per second squared (ft/s²). For instance, an object starting from rest would be moving at 9.8 m/s after one second, and 19.6 m/s after two seconds.
Factors Influencing Falling Speed
While gravity provides a constant downward pull, an object’s falling speed in a real-world scenario is significantly influenced by air resistance. Air resistance is a type of fluid friction that opposes an object’s motion through the air, becoming more significant as speed increases.
The amount of air resistance depends primarily on an object’s shape, cross-sectional area, and surface texture. For example, a flat sheet of paper encounters more air resistance than a crumpled ball of the same paper. A rough surface also experiences more drag than a smooth one. An object’s density, its mass per unit volume, also affects how air resistance impacts its fall. Denser objects have more gravitational force relative to the air resistance they encounter, allowing for a faster descent in typical atmospheric conditions.
Understanding Terminal Velocity
As an object falls, its speed increases, and so does the force of air resistance. Eventually, the upward force of air resistance equals the downward force of gravity, making the net force on the object zero. At this point, the object stops accelerating and falls at a constant maximum speed, known as terminal velocity.
Terminal velocity depends on an object’s weight, shape, and cross-sectional area. For example, a skydiver accelerates until air resistance matches gravity, then maintains a steady descent speed. A heavier, more streamlined object achieves a higher terminal velocity than a lighter, less aerodynamic one. Raindrops also reach terminal velocity, preventing them from continuously accelerating and hitting the ground with destructive force.
Common Misconceptions About Falling Objects
A common misconception is that heavier objects always fall faster than lighter ones. While a bowling ball clearly falls faster than a feather in everyday observations, this difference is due to air resistance, not gravity.
In a vacuum, all objects fall at the same rate. Galileo Galilei famously theorized this, suggesting a feather and a hammer would hit the ground simultaneously without air resistance. Astronaut David Scott confirmed this on the Moon during Apollo 15, dropping a hammer and a feather that landed at the same time. Earth’s atmosphere creates drag, disproportionately affecting lighter or less aerodynamic objects and making them appear to fall slower.