Module 9

How Far Does a Bungee Cord Stretch?

Student Guide

Bill Edelbrock, Eugene Judson, Terry Leyba, Jeff Turley

INTRODUCTION

You have all seen or perhaps experienced Bungee Jumping. One end of a bungee cord is securely fastened to a "jumper's" ankle, and the jumper is released from a high tower. The jumper plummets toward terra firma in an attempt to enrich his/her life through sheer terror. If all goes well, just before the jumper produces a crater in the ground, the bungee cord becomes fully stretched, the jumper's motion is reversed, and he/she suddenly rockets skyward. How did the designer of the Bungee Jump, who after all must have been a physics student, know to construct the Jump so that the jumper's head nearly touches the ground just before being pulled back up (It's bad for business if the jumper dies)? Since we cannot Bungee Jump in the class, we will examine this phenomenon using springs.

OBJECTIVES

To understand the potential and kinetic energies of a bungee jumper.

To investigate the factors that determine the maximum extension of a spring suspended vertically.

To model a bungee jump by finding a mathematical function to represent the extension of a spring as a function of the forces acting on it.
To build a simulation of a bungee jump, and to test your model.

MATERIALS

various springs	TI-82 or TI-83 graphing calculator
CBL	force probe
PHYSICS program	various masses
mass hanger	meter stick
rods	clamps
bungee cords	raw egg
table	string
carbon paper

PROCEDURE Part I

Discuss with your group what is happening to the bungee jumper at the top of the tower and at the bottom of the fall. Include in your discussion concepts such as forces acting on the jumper, the energy at the top, middle and bottom of the jump, the motion at various places in the fall. Prepare a brief summary of your group's discussion for the class.

PROCEDURE Part II

1. Perform an experiment to determine the extension of a spring as a function of the weight suspended from it. Use the TI-82/83 calculator running the PHYSICS program.

2. Construct a model to the data you collect by finding a mathematical function which you can use to predict the maximimum extension of the spring as a function of the suspended weight.

3. Use your model to predict the maximum amount that the spring will stretch when any mass is suspended from it.

The Egg Test:

Your instructor will give your group a new spring and a raw egg.
Design an experiment which will allow the mass to stretch the spring just far enough to touch the top of the egg located beneath the spring.
Attach a piece of carbon paper to the bottom of the weight, so that the mass attached to the spring will leave a mark on the egg when the two come in contact. The challenge is to make a mark on the egg without cracking the egg! When your experiment is ready, notify your instructor who will release the weight to test whether your prediction was successful. You cannot use trial and error! Good luck!
(Be sure to place the raw egg in the plastic tub beneath the suspended weight.)

4. With your group prepare a whiteboard presentation summarizing the model you used to predict the maximum extension of the spring.

Last modified 12 Aug 1997
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