Abstract
This bungee jumping model improves the stretch prediction accuracy of prior models by including the effects of: rubber viscoelasticity, stiffness nonlinearities, jumper air drag, and jumper horizontal push-off. Bungee (bungy) cords are made from rubber, a viscoelastic material whose stiffness is a function of the number of cycles (cycle effect), the time interval since the last cycle (interval effect), strain rate, and temperature. Stiffness was measured, on an MTS machine, over 100 cycles at four intervals (1, 5, 60, 1440 min), three strain rates (0.17, 1.5, 5.0 s−1) and constant temperature (20.5°C). At a constant cycle interval and strain rate, rubber stiffness decreased 9.8% from the 10th to the 100th cycle. This decrease was linear with the logarithm of the cycle number. Stiffness recovered 6.5% after 24 hours of non-use. Neglecting viscoelastic effects causes significant stretch-prediction errors of -11.0% (cycle effect), -3.2% (interval effect), and +1.6% (strain rate). Less significantly, neglecting jumper air drag, jumper push-off, and stress-strain nonlinearities cause prediction errors of +1.9%, +0.7%, and +0.2%, respectively. These errors are based on a typical cord, of unstretched length 7.5 m, that elongates 250%. For accurate stretch prediction, with typical sized bungee cords, viscoelastic effects are both more important and easier to implement than air drag and stress-strain non-linearity.
Similar content being viewed by others
References
ASTM (2002) Standard test methods for rubber thread. D 2433-93; Volume 09.02, p. 106.
Brown, R.P. (1996)Physical Testing of Rubber (3rd edn.). p. 149. Chapman & Hall, London, UK.
Craig, R.R. Jr. (1996)Mechanics of Materials. p. 101. John Wiley & Sons, New York, NY, USA.
Cross R. (2000) Tension loss along a string.American Journal of Physics,68 (12), 1152–1153.
Den Hartog, J.P. (1952)Advanced Strength of Materials. p. 117. McGraw Hill, New York, NY, USA.
Ferry, J.D. (1980)Viscoelastic Properties of Polymers (3rd edn.). John Wiley & Sons, New York, NY, USA.
Freakley, P.K. & Payne, A.R. (1978)Theory and Practice of Engineering with Rubber. Applied Science Publishers, London, UK.
Gent, A.N. (2001)Engineering with Rubber: How to Design Rubber Components. (2nd edn.). p. 182. Hanser Gardner Publications, Cincinnati, OH, USA.
Hoerner, S.F. (1965)Fluid-Dynamic Drag: Practical Information on Aerodynamic Drag and Hydrodynamic Resistance (2nd ed.). pp. 3–14. Published by the Author, Midland Park, NJ, USA.
Kagan, D. & Kott, A. (1996) The greater-than-g acceleration of a bungee jumper.The Physics Teacher,34, 368–373.
Kockelman, J.W. & Hubbard, M. (2004) Bungee jumping cord design using a simple model.Sports Engineering, 7 (2), 89–96.
Menz, P.G. (1993) The physics of bungee jumping.The Physics Teacher,31, 483–487.
Motion Analysis Corporation (2002)EVa 7.0 Motion Analysis Reference Manual. Santa Rosa, CA, USA.
Mullins, L. (1969) Softening of rubber by deformation.Rubber Chemistry & Technology,42, 341.
Palffy-Muhoray, P. (1993) Problem and solution: acceleration during bungee-cord jumping.American Journal of Physics,61, 379 and 381.
Roberts, A.D. (1988)Natural Rubber Science and Technology. Oxford University Press, Oxford, UK.
Shevell, R.S. (1989)Fundamentals of Flight (2nd edn.). p. 422. Prentice Hall, Englewood Cliffs, NJ, USA.
Steidel, R.F. Jr. (1989)An Introduction to Mechanical Vibrations (3rd edn.). pp. 83–85. John Wiley & Sons, New York, NY, USA.
Strnad, J. (1997) A simple theoretical model of a bungee jump.European Journal of Physics,18, 388–391.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Kockelman, J.W., Hubbard, M. Bungee jump model with increased stretch-prediction accuracy. Sports Eng 8, 159–170 (2005). https://doi.org/10.1007/BF02844016
Issue Date:
DOI: https://doi.org/10.1007/BF02844016