Slow Drop


To build a device that will slowly fall inside a vertical plastic tube.

Permitted Materials
  1. Cloth, wood, metal and dental floss (waxed or plain)
  2. Parts may be used from commercial objects (toys, models, etc.) but the frame holding the device together must be constructed, not purchased whole.
Other Constraints
  1. No energy sources other than gravity may be used.
  2. The device must fit completely in a tube 10 inches long with a 4-inch internal diameter.
  3. The device may touch but not scratch, pit or dig into the internal surface of the competition tube.
  4. The device must be made of (contain) some combination of cloth, wood and metal. Dental floss is optional. No other materials are allowed (plastic, ceramic, rubber, etc.)
  5. The mass of the device must be equal to or greater than 200 grams.
Testing Procedure
  1. A transparent plastic tube four inches in internal diameter and six feet long will be mounted vertically at the edge of a table. One foot from each end, laser diodes and photo detectors, on opposite sides of the tube, will be mounted to start and stop timing the motion of the falling device. The mass of the device will be measured with a digital balance. Contestants will place their device in the first foot of the tube and release it. Once the device has been released, contestants may not touch the tube. Timing will commence when the first laser beam is broken and stopped when the second laser beam is broken.
  2. Each contestant will be given three attempts. The three attempts will be scheduled consecutively; however, contestants may opt to delay the third attempt to make minor repairs or adjustments. The longest time of the three will be used as a final score.
  3. The high score wins. In the event of a tie, the second best of the three attempts will be the tie breaker. If the device becomes lodged (no visible motion for 3 seconds or more) in the tube, that attempt will be recorded as a scratch.
  4. To test the device in your own school a section of four inch diameter plastic sewer pipe, available at most hardware stores, will be nearly the same as our transparent tube. Stated tube diameters may vary slightly, so it is important that the device can be adjusted to match different four inch tubes.
  5. Only two practice drops in the tube, prior to the competition, will be allowed to adjust the device to match the tube diameter.
Testing Equipment – Timer
College of Saint Benedict
Saint John’s University

Jim Crumley
Chair, Physics Department
SJU PEngl 107
Physics Department