Description: Strings with weights attached at equal, and at squared intervals are dropped. The difference in time between impacts is audible.

String1 has six 1.1 inch diameter wooden balls, painted red, attached at equal intervals of 50 cm (total length 250 cm). String 2 has six balls, painted yellow, attached at 0, 10, 40, 90, 160 and 250 cm. Bring the different spacings to the students attention.

Stand on the bench and hold string 1 so that the bottom ball is just above the sounding board (the top of a Xerox box works well). Allow the string to drop. Impacts will be heard at 0, 0.32, 0.45, 0.55, 0.64 and 0.71 seconds after dropping. Students should be able to hear that the time interval between successive impacts gets smaller. It is worth repeating this to allow students to train their ears to hear the intervals. To quote Taylor "Although very rapid, the human ear-brain system can detect the time intervals and it is abundantly clear that the time intervals become shorter as the weights that started off higher reach the floor."

Repeat with string 2. Students should hear the impacts uniformly spaced. The interval is one seventh of a second.

Meiners suggests using a microphone and an oscilloscope. Edge suggests shifting position of one of the weights to demonstrate the sensitivity of the ear to non-uniform intervals. According to him 20% is easily detectable.

Cautions: Don't fall off the bench.

Concepts demonstrated: Acceleration of falling bodies

Setup Time: Short

Difficulty/Commitment: Straightforward

Visibility: Visible

Related demonstrations:

References: PIRA 1C20.20
Video Encyclopedia 01-12
Sutton M-84; Meiners 7-1.12; DHP Mb-12; DaR M-094; String and Sticky Tape 1.22 (from TPT 16(4), 233 (April 1978)); Rogers "Physics for the Inquiring Mind" Problem 22, p24; Joseph ea "Sourcebook" p369; Taylor 1.22 p46; Miller p22