One of the most suprising things we learn in Physics class is that the acceleration due to Earth’s gravity is constant for any mass (9.81 m/s/s). Gallileo demonstrated it in 1589 by dropping objects of different mass from the Leaning Tower of Pisa. Sure, a heavier mass will do more damage, but they all reach the ground at the same time.
One explanation for why we struggle with it is that we live in a world full of air.
Very light objects are more susceptible to air resistance. While the gravitational acceleration of a feather is the same as the gravitational acceleration of a bowling ball, the actual force exerted is proportional to their mass [ F= mass(variable) x acceleration(constant) ].
In the case of a feather, the force of the air resistance is significant when compared to the gravitational force – so it falls more slowly. This is how a parachute works: by catching more air.
In our experience, a feather falls more slowly because of air resistance.
But what if you remove the air? Brian Cox demonstrates for the BBC series Human Universe, with the aid of a very large vacuum chamber, and some amazing slow-motion photography.
[youtube]https://www.youtube.com/watch?v=E43-CfukEgs[/youtube]
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