1C20.10 - Free-Fall in a Vacuum (Penny and Feather Demo)

Code Number:
Demo Title:
Free-Fall in a Vacuum (Penny and Feather Demo)
Acceleration Due to Earth's Gravity is Constant
Area of Study:
Vacuum Tube with Feather & Penny, Vacuum Pump, Book, and Piece of Paper.

The vacuum tube may have to be taken apart for cleaning.  Check the oil in the vacuum pump and maintain at the proper level.  Using the triangular variable wedge will help insure that the tube will not roll off the table.

A small ball of cotton may be substituted for the feather.

A way to do this without the vacuum system is to take a large text book and place a piece of paper directly on top of it.  When this is dropped the paper will drop at the same speed as the textbook and stay directly on top of the book.

  • Hollis Williams, "A High-Speed Test of the Equivalence Principle", TPT, Vol. 60, #7, Oct. 2022, p. 594.
  • Elida de Obaldia, Norma Miller, Fred Wittel, George Jaimison, and Kendra Wallis, "Bridging the Conceptual Gap Between Free Fall and Drag-Dominated Regimes", TPT, Vol. 54, #4, Apr. 2016, p. 233.
  • Christopher L. Vaughan and Moshe Nissan, "Teaching Mechanics with a Digital Camera", TPT, Vol. 25, #7, Oct. 1987, p. 445.
  • "M-088: Coin and Feather in Tube", DICK and RAE Physics Demo Notebook.
  • George M. Hopkins, "Falling Bodies--Inclined Plane--The Pendulum", Experimental Science, p. 38.
  • Julien Clinton Sprott, "1.1, Guinea and Feather Tube", Physics Demonstrations, ISBN 0-299-21580-6, p. 2.
  • John Henry Pepper and Henry George Hine, "Gravitation", The Boy's Playbook of Science, p. 14.
  • "The Paradox of the Falling Bodies", The Boy Scientist.
  • Ron Hipschman, "Falling Feather", Exploratorium Cookbook III, p. 137-1.
  • "Falling Feather", The Exploratorium Science Snackbook, p. 50-1.
  • Christopher P. Jargodzki and Franklin Potter, "397. Was Galileo Right?", Mad About Physics, p. 154, 297.
  • Borislaw Bilash II and David Maiullo, "Falling Together", A Demo a Day: A Year of Physics Demonstrations, p. 27.
  • "This Month in Physics History", APS News, Vol. 26, #2, Feb. 2017, p. 2 - 3.
  • Borislaw Bilash II, “Falling Together“, A Demo A Day – A Year of Physical Science Demonstrations, p. 238.
  • "Guinea and Feather Tube", Pike's Illustrated Catalogue of Scientific & Medical Instruments, 1984, p. 207.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.