Our Planet

A Bowling Ball and Feather Falling in a Vacuum (video)

by Our Planet


It’s one of the basic Newton laws: how fast something falls due to gravity is determined by a number known as the “acceleration of gravity”, which is 9.81 m/s2 at the surface of Earth. The acceleration of gravity, shortly “a” means that in one second, any object’s downward velocity will increase by 9.81 m/s because of gravity. The gravity accelerates everything at exactly the same rate.
This also means, a heavy object like a bowling ball and a lightweight object like a feather should fall down with the same speed, regardless of their shapes. But we see this phenomenon very rarely in our daily lives. The reason is: the air resistance. That’s why people (including Aristotle) thought that the heavier objects fall faster for thousand of years.

It seems Galileo Galilei was the first person noticed that different things fall at the same rate. According to a biography by Galileo’s pupil Vincenzo Viviani, in 1589 the Italian scientist had dropped two balls of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass. But there was really no explanation of why until Sir Isaac Newton developed three physical laws that together laid the foundation for classical mechanics now we know as Newton’s laws of motion.

Galileo's Leaning Tower of Pisa experiment
In the presence of the Grand Duke, Galileo Galilei makes Leaning Tower of Pisa experiment. A painting by Luigi Catani ( 7 November 1762 – 17 December 1840), an Italian painter. Photo from: museogalileo.it

In the amazing video from the BBC below, physicist Brian Cox visits Space Power Facility in Ohio, a vacuum chamber built by NASA in 1969. It stands 122 feet (37 m) high and 100 feet (30 m) in diameter, enclosing a bullet-shaped space. With a volume of 22,653 cubic meters, it’s the largest vacuum chamber in the world. It was originally commissioned for nuclear-electric power studies under vacuum conditions, but was later decommissioned. Recently, it was recommissioned for use in testing spacecraft propulsion systems. Recent uses include testing the airbag landing systems for the Mars Pathfinder and the Mars Exploration Rovers, Spirit and Opportunity, under simulated Mars atmospheric conditions.

Cox makes an experiment: first, he drops a bowling ball and a feather under normal conditions (with air in the chamber), and then he repeats it in a vacuum, after all the air has been sucked out of the chamber. It’s really worth to watch.