A water level smoothed in this way represents an equipotential surface in which communicating vessels have exactly the same value of gravity potential . A distinction must be made between the terms “water level” (see below) and water level . The theory of equipotential surfaces applies in all types of liquid containers or in pipelines when they are not under pressure and have no noticeable adhesion or friction .
When forces other than air pressure act, currents and waves occur. By averaging repeated measurements over a certain period of time, it is possible to determine the undisturbed surface that is normal to the plumb lines everywhere . For more demanding tasks, a so-called reduction of the measurement data is carried out instead of averaging , whereby the disruptive forces must be modeled mathematically .
Difference between water level and water level
In contrast, the term " water level " means something else:
- it can to a defined height above the sea level , such as the mean sea level , or the meters above Adria based or be converted
- it can be a gradient and therefore a flow exist
- some of the above averages are not carried out depending on the application,
- so that the “water level of a body of water ” changes at least with the tides - see high and low water , ebb and flow .
Idealized, smooth surface
While on a small scale - for example in laboratory technology - only minor influences disturb the water level (for example the edge and surface tension ), this is different in nature. There the water level is defined as the dynamic mean value of an idealized, smooth surface and, above all, abstracted from the following influences:
- short-period swell (but not for periods longer than about 1 minute)
- Disruptions from vehicles and their possible congestion effects
- short-term wind influences such as gusts
- for local applications, possibly from the earth's curvature (when considering the earth's curvature , which is almost 1 mm at 100 meters, a horizontal tangential plane becomes a level surface of the earth)
- mostly also from long-term wind congestion effects , such as drift current and compensation current in closed seas
Before polished metals and glasses were made usable, water levels were used as mirrors , which is thematized in the ancient Narcissus saga : Narcissus sees himself in the water level for the first time. In the 19th century, fictional water levels served to justify the direction of illumination of the limelight in the theater. To this day, the reflections from water levels are used in landscape architecture or light art and are a challenge for artistic images.
Science and psychology
Deviations from the normal of the horizontal smooth surface play a role in numerous experiments and scientific demonstrations. Isaac Newton used a water mirror in his bucket experiment to show the gravitational forces in a rotating vessel. Jean Piaget put test subjects to the test in connection with his “Theory of Mental Development” by having them draw the water level in an inclined glass.