1F20.36-Pen and Hoop

1f2036_pen_and_hoop_2 1f2036_pen_and_hoop

Video: Watch this demo

Description: A quick and impressive demonstration of inertia (Newton’s First Law).
When the hoop is yanked out from beneath the pen, the pen will fall directly into the narrow opening of the bottle.


  • Pen with one FLAT end.
  • Wooden hoop
  • Bottle

Setup Procedure:

  1. Balance the hoop on the bottle. The hoop should be labeled with a “B” for the bottom and a “T” for the top. This is so you know exactly where to place the pen to be directly above the bottle.
  2. Balance the pen on the top of the hoop. (This can take a while, especially in front of a class)

Demonstration Procedure:

  1. Quickly snatch the hoop out from under the pen, grabbing the hoop from the INSIDE, and yanking it parallel to the plane of the hoop, so as not to create a torque on the hoop. (Grabbing the hoop on the inside is necessary because the hoop will actually bend a little, and will thus DROP from underneath the pen before moving out horizontally. If you grab the hoop from the outside, the bending will launch the pen upward and cause the demo to fail. Also, your hand might get in the way.)