In a vacuum, a feather and a bowling ball fall at the exact same speed.

This phenomenon is rooted in the principle of equivalence, which was famously tested by Galileo Galilei in the late 16th century. According to Newton's Second Law of Motion and the Law of Universal Gravitation, the mass of an object cancels out when calculating its gravitational acceleration. This means that in the absence of external forces like air resistance, every object near Earth's surface accelerates downward at approximately 9.8 meters per second squared.A modern and visually stunning demonstration of this occurred at NASA's Space Power Facility in Ohio, which houses the world's largest vacuum chamber. Measuring 100 feet in diameter and 122 feet tall, the chamber was pumped down to a near-perfect vacuum for the experiment. When a cluster of feathers and a heavy bowling ball were released simultaneously from a height, they stayed perfectly level throughout the entire drop.Physicist Brian Cox showcased this experiment for the BBC program 'Human Universe' in 2014 to illustrate Einstein's General Theory of Relativity. Einstein proposed that gravity is not a force pulling on objects, but rather a curvature of spacetime. Because both the feather and the ball are following the same curved path through space, they must move identically when no other forces are present. This experiment remains one of the most fundamental proofs of classical and modern physics.