Student Experiment on Wastewater

The problem of buoyancy in basins, shafts, and pipes—caused, among other things, by groundwater—can be demonstrated in a simple model experiment. In this experiment, a basin surrounding the shaft or pipe model is filled with water, and the time (water level) at which the model begins to float is recorded.

The scientific principles (Archimedes, Newton), mathematical calculations (algebra, geometry, proportionality), and engineering experiments (measured variables: weight, dimensions, water levels) are well-suited for middle school students. The values measured in the model experiment should be compared with the theoretical calculation. The experiment can be conducted for various objects (pipe materials, shafts, empty, filled, weighted, etc.). Manual calculations can be performed using MS Excel. The applicability of the model to real-world situations should be discussed, as should the use of engineering tools (buoyancy calculators provided by pipe manufacturers) and measures to address the issue.

Experimental Results

Example result: The calculation indicates that the plastic manhole (170 g) will “float” at a water level of approximately 4 cm. This is confirmed by the model experiment. Weighing down the manhole prevents it from “floating.” The topic of “buoyancy” also applies to pipes, though to varying degrees depending on the pipe material. Empty and lightweight pipes are “more likely” to float. The density of the liquid also plays a role.

Relevance to the Field

The relevance to the field may arise from high groundwater levels and during high water/flooding. This particularly affects basins that are not constantly filled (RÜBs/RRBs), as well as plastic manholes and pipes. In sewer construction, buoyancy must be taken into account when using liquid soil.