Why do light and heavy objects fall at the same time?
The change in speed due to gravity is the same for all objects because the force and inertia acting on an object are proportional to the object’s mass.
- The force to accelerate an object is gravity. This force is proportional to mass. (The heavier the thing, the stronger it is pulled to the Earth.)
- The property that opposes the acceleration of an object is inertia. Inertia is also proportional to mass. (The heavier the object, the slower it accelerates.)
\[Change\,in\,motion \propto \frac{Gravity(proportional\,to\,mass)}{Inertia(proportional\,to\,mass)}\]
Therefore, an object’s free fall rate is independent of its mass because gravity and inertia cancel each other out.