# SCIENCE BEHIND ZIP LININg

## Introduction

One question that every student has wondered at some point in their schooling is, “When am I ever going to actually use this stuff?” The Science Behind Zip Lining website serves as one answer to that question. Its purpose is to demonstrate how the Science, Technology, Engineering, and Mathematics (STEM) principles that you have learned apply to real-world situations.

## Design of a Zip Line

Every zip line consists of a trolley attached to a steel cable that is typically covered with a vinyl coating. For safety, the rider should be wearing a helmet, gloves, and a harness which is used to keep the rider attached to the trolley. Gravity propels the rider from start to finish.

The first step when designing a zip line is to identify the parameters involved. Some of the questions that need to be answered are:

• How long of a distance will the zip line span?
• How high should the start and end points be?
• What is the topography of the ground relative to the zip line cable?
• What will the start and end points be attached to and how can they be secured?
• How much tension should there be to give the zip line an appropriate slope?
• What will the weight limitations be?

* WARNING: Always consult with an industry professional before attempting to design or build your own zip line.

The zip line illustrated below covers a horizontal distance of 255 meters (m) and has a vertical drop of 16 m to the lowest point. The start point is 13 m above the ground and the end point is 11 m above the ground. Both points have been securely anchored using trees. Notice that the topography of the ground has a slightly downward grade from the start point to the end point. There is an elevation drop of 12 m. This helps achieve a sufficient slope, approximately 4 degrees in this example, without causing the cable to be extremely high off the ground at the start point. For safety reasons, a weight range of 70 to 250 pounds is acceptable for a zip line this size.