A 6-feet long Plexiglas tube containing a "coin" and "feather" is evacuated. The "coin" and "feather" fall at the same rate. When air is introduced into the tube, the "feather" falls at a slower rate.

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It may not be intuitive, but drop a hammer and a feather and – in the absence of air resistance – they will hit the ground at exactly the same time. This is a key principle of physics known as ...