In a vacuum, all objects fall at the same rate due to the uniform acceleration produced by gravity.

This phenomenon is a fundamental principle of physics, first articulated by Galileo Galilei and later validated by Albert Einstein in his theory of general relativity. In a vacuum—where there is no air resistance or friction to impede motion—all objects, irrespective of their mass, will fall at the same rate. This rate is known as the acceleration due to gravity, which on Earth is approximately $9.81 \, \text{m/s}^2$.

The underlying reason for this uniformity is that gravity acts equally on all objects. In a vacuum, the only force acting on a falling object is gravity itself. According to Newton’s second law of motion, the force acting on an object can be expressed as:

This means that the gravitational force acting on an object is directly proportional to its mass. For instance, if one object has twice the mass of another, it will experience double the gravitational force. However, because this more massive object also has greater mass, it requires twice the force to achieve the same acceleration. Consequently, these two effects balance each other out, resulting in all objects falling at the same rate, regardless of their mass.