This might seem surprising because, under normal Earth conditions, we see feathers float gently to the ground while bowling balls fall quickly. That happens because of air resistance—a force that acts against the motion of objects moving through air. Feathers, being light and having a large surface area, are greatly slowed down by air. Bowling balls, being heavy and compact, are hardly affected by it.
But in a vacuum, there is no air, and therefore no air resistance. The only force acting on both the feather and the bowling ball is gravity, which accelerates all objects equally regardless of their mass. This concept was famously demonstrated by Galileo Galilei in the 17th century and later more dramatically confirmed in 1971 by astronaut David Scott on the Moon (which has no atmosphere). He dropped a feather and a hammer during the Apollo 15 mission, and they hit the lunar surface simultaneously.
The principle behind this is explained by Newton’s laws and the equivalence of inertial and gravitational mass. The acceleration due to gravity (about 9.8 m/s² on Earth) is the same for all objects, regardless of how heavy they are—as long as no other forces (like air drag) are involved.
👉 In a vacuum, a feather and a bowling ball fall at the same rate and hit the ground at the same time.
Both the feather and the bowling ball will strike the ground simultaneously if dropped in a vacuum.
This fascinating phenomenon occurs because of how gravity works when no other forces, like air resistance, are present. It’s a core idea in physics, often linked to Galileo Galilei’s insights and memorably shown by NASA astronauts on the Moon.
Here’s the science simplified:
- Universal Acceleration by Gravity: The pull of gravity causes all objects to accelerate at the exact same rate, irrespective of how heavy they are. While it’s true that gravity exerts a stronger pull on a massive item (the bowling ball) compared to a lighter one (the feather), the bowling ball’s greater mass also means it has more inertia – it’s more resistant to changes in its motion. These two aspects perfectly balance out.
- The Absence of Air Resistance is Key: On Earth, under normal conditions, we see a feather drift down slowly while a bowling ball plummets. This difference is entirely due to air resistance. Air pushes against moving objects, and this force has a far greater impact on objects that are light and have a large surface area for their weight (like the feather) than it does on dense, heavy items (like the bowling ball).
- The Vacuum Difference: A vacuum is an environment with no air. When you remove the air, you remove air resistance. Consequently, the sole force influencing the falling objects is gravity. Because gravity makes everything accelerate equally when unopposed, the feather and the bowling ball speed up at the same pace and therefore complete their fall at the exact same moment.
A compelling real-world demonstration of this took place during the Apollo 15 lunar mission in 1971. Astronaut David Scott dropped a geological hammer and a feather. In the airless environment of the Moon, television cameras captured them hitting the dusty surface together.
In a vacuum, the only force acting on the feather and the bowling ball is gravity, which causes all objects to accelerate toward the ground at the same rate, approximately 9.8 m/s² on Earth. This principle was first formalized by Galileo Galilei, who theorized that, absent air resistance, objects of different masses fall at the same speed. His ideas challenged the earlier Aristotelian view that heavier objects fall faster.
The reason a feather and a bowling ball behave differently in Earth’s atmosphere is due to air resistance. The feather, with its large surface area and low mass, is affected greatly by air, causing it to flutter and fall slowly. The bowling ball, being dense and heavy, is less influenced by air resistance and falls more directly. In a vacuum, these differences are eliminated, as there are no air molecules to impede the motion of either object.
The Apollo 15 experiment is a famous real-world demonstration of this concept. On the Moon, which has no atmosphere, astronaut David Scott dropped a falcon feather and a hammer from the same height. Both objects hit the lunar surface at the same time, confirming Galileo’s hypothesis in a near-perfect vacuum environment. The Moon’s gravity is about 1/6th that of Earth’s (1.62 m/s²), but the principle holds: the acceleration due to gravity is independent of mass.
Mathematically, the time it takes for an object to fall a certain distance in a vacuum can be described using the equation of motion:
[ t = \sqrt{\frac{2h}{g}} ]
where ( t ) is the time, ( h ) is the height, and ( g ) is the acceleration due to gravity. Since ( g ) is the same for both the feather and the bowling ball, and assuming they are dropped from the same height ( h ), the time ( t ) will be identical for both.
If you were to conduct this experiment in a vacuum chamber on Earth, such as those used in physics demonstrations, you’d observe the same result. For example, the University of Queensland’s physics department has conducted experiments in large vacuum chambers where feathers and heavy objects are dropped, consistently showing they hit the ground simultaneously when air is removed.
This principle also applies universally, whether on Earth, the Moon, or any other body with gravity, as long as no other forces (like air resistance or magnetism) interfere. It’s a cornerstone of classical mechanics and was later refined by Newton’s laws of motion and Einstein’s theory of general relativity, which describe gravity as the curvature of spacetime affecting all masses equally.