1G20.38 - Einstein's Birthday Present

Code Number:
Demo Title:
Einstein's Birthday Present
Gravitational Acceleration and Freefall
Area of Study:
Plexiglas Cup on Pole Apparatus.

Hang the ball outside the cup and lift as high in the air as you can while holding on to the end of the handle. Note that the spring can not pull the ball back into the cup due to the influence of gravity. Drop the apparatus and catch it below the cup before it hits the ground. Careful observation will reveal that the ball is pulled into the cup by the spring during freefall.

  • Efstratios Kapotis and George Kalkanis, "Einstein’s Elevator in Class: A Self-Construction by Students for the Study of the Equivalence Principle", TPT, Vol. 54, #7, Oct. 2016, p. 404.
  • Clyde J. Smith, "Weightlessness for Large Classes", TPT, Vol. 27, #1, Jan. 1989, p. 40.
  • D. Easton, "Weightlessness and Free Bodies", TPT, Vol. 21, #8, Nov. 1983, p. 521.
  • R. D. Edge, "Weightlessness and Other Ideas", TPT, Vol. 19, #3, Mar. 1981, p. 190.
  • Johanna L. Miller, "Free-Falling Nanoparticle Helps to Detect Tiny Forces", Physics Today, Vol. 71, #10, Oct. 2018, p. 19.
  • M-188/S-055, "Water/Masses in Styrofoam Cup",  DICK and RAE Physics Demo Notebook.
  • "Weightlessness in Free Fall", PIRA Newsletter, Vol. 3, #19, Jan. 25, 1990, p. 2.
  • R. D. Edge, "Experiment 1.28:  Weightlessness", String and Sticky Tape Experiments.
  • Julius Sumner Miller, Q52 & A52, Millergrams I – Some Enchanting Questions for Enquiring Minds, p. 37 & 95.

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