B4-04: SPRING AND STRING THING

ID Code: B4-04
Purpose: Illustrate series and parallel springs in a counterintuitive way.
Description: Two springs connected in series support a weight. Strings slightly longer than the springs are connected in parallel with each spring, as photographed. The connecting wire loop between the two springs is then removed, forming two separate parallel routes, each consisting of a spring and a string in series.

Comparing the final configuration with the initial configuration, will the weight be higher, lower, or at the same vertical position?

The pictures above show the system in its initial and final configurations, as well as in detail of how the springs and strings are coupled at the center.

This demonstration is an analog to paradoxical behavior in complex series/parallel arrangements for other mechanical, hydraulic, and electrical systems. Perhaps the most notable is Braess' paradox for traffic flow. In certain types of congested traffic flow situations, opening an additional new route between two points may actually increase the average time taken to travel between the two points.

Availability:Available

See the Physics Question of the Week for 3/3/2014 for an example of how this demonstration can be used in class interaction and discussion: lecdem.physics.umd.edu/question-of-the-week-archive.html