Backyard Waterslide Engineering

By Dan Feins, Middle School Science

Engineers ask critical questions about what they want to create, whether it be a skyscraper, amusement park ride, bicycle or smartphone. These questions include: What is the problem to solve? What do we want to design? Who is it for? What do we want to accomplish? What are the project requirements? What are the limitations? What is our goal?

The seventh-grade class at the Beverly campus began an engineering unit in the New Year. After a very brief discussion, the class determined the problem to solve was how can we build a waterslide in our own backyard. Based on previous waterslide experiences, the students’ initial concept was to connect three or four “normal” plastic slides together, support those slides with wooden trusses, and have a long ladder to reach the top. Water would arrive at the top via a series of extension hoses and be deposited at the bottom into a pool.

Practical issues were discussed during the next class. The students were confronted with several issues, most of which involved physics and cost. For example, a person sitting at the top of a waterslide has inertia that they must overcome to start down the slide. Should the water give them a push, or should the person push themselves? Friction needed to be overcome on the way down the slide, and that required more water than could be achieved through a garden hose. And then there was cost. Although no budget had been set at this point, the team knew that money was not going to be unlimited.

Research commenced via Chromebooks. The team determined that a “trash hose” connected to a “trash water pump” would push the water up to the slide and then down the slide with enough pressure to move a person along. Cost comparisons were made in terms of buying or renting the trash water pump. The team leaned in the direction of renting because the waterslide would only be used for certain parts of the year, and even then, on certain days within those parts.

The team took some time to view videos of successful waterslides from around the world and from people’s backyards. The students were struck by one video which showed a backyard waterslide that was built on sloped ground, eliminating the need for plastic slides, a support structure, a ladder, and decreasing the size of trash water pump required. The team was introduced to the most critical aspect of engineering: it is an iterative process, meaning that we repeat the steps as many times as needed, making improvements along the way as we learn from failure and uncover new design possibilities to arrive at great solutions

At the next class meeting the old design was scrapped in favor of one that could be built along the ground and run down a hill. The students drafted up some designs and settled on a waterslide that twists and turns and would run the length of the hill, culminating in a shallow pool at the end. During the next class, with some students out due to illness, one of the students worked on their prototype. After several valiant attempts to construct a twisting and turning waterslide, it became evident that such a construction may not be possible for their prototype, given the materials at hand, and it may in fact be prohibitively difficult for full scale construction as well.

The next couple of classes the students turned their attention to building a linear waterslide. Tests of the waterslide were made using water from a pitcher poured down the slide from the top. The students quickly learned that creating a leak proof waterslide required a lot of work and attention to detail. But having stopped the leaks, the next test involved a scale stand-in model (a Playmobile figure) to start at the top of the slide and move down the slide with the flowing water from the pitcher and end in the shallow pool. Several iterations followed as the figure was stuck at the top of the slide or became stuck as it moved down the slide.

The students persevered until the plastic figure completed a transit of the waterslide on three separate trial runs. Success! But now could this be built in the backyard of one of the students? A site was chosen, and the student brought in pictures of where the waterslide Dan's Blogwas to be lodged. Unfortunately, the nature of the incline and the lighting at the time the photos were taken made it difficult to visualize how the waterslide was going to work in that area. There was also the matter of potential environmental issues if the area was going to be dug up and subjected to inordinary amounts of water and foot traffic. The students and the teacher decided that a trip to the proposed waterslide site was warranted.

The class set off a bright and cold February morning to the house of one the students. There, we were welcomed into the student’s home by her mother who gave us a brief tour, including a visit with the resident velvety soft rabbit and working cat. Once in the backyard, we walked the terrain upon which the student had done some preliminary clearing. This made it easy for us to measure the length of the hill (90 feet) and take some Dan's Blogsoil and leaf samples for analysis after February break. We returned to the house to warm ourselves with some freshly baked cinnamon bread. We said our goodbyes to the bunny, the cat, and mom, and returned to the school.

In the best tradition of engineering, the students now have new questions: will the results of the soil and leaf testing be in favor of construction? How much it will cost to build a 90-foot waterslide? How much water pressure do you need to move a person from the top to the bottom? What happens to all that water in the pool at the end of the waterslide? Will Mom and Dad really want to build a 90-foot waterslide in their backyard? Fortunately for the students, engineering is an iterative process, so a “no” at any of those points does not necessarily mean the project needs to be cancelled, only reimagined.