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University of Bergen
Geophysical Institute

24 days of kitchen oceanography

Each day a new experiement will be posted here. Reveal what is hidden behind the windows by clicking on the arrows below.

Introduction
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
Day 11
Day 12
Day 13
Day 14
Day 15
Day 16
Day 17
Day 18
Day 19
Day 20
Day 21
Day 22
Day 23
Day 24

Main content

Hydraulic jump

Day 7
07.12.2020

What is that circle in the sink?

Hydraulisk sprang
Photo:
Mirjam Glessmer, GFI

Experiment 7:

We just have to open the tap, and this circle appears!

Depending on how fast water flows, it is faster or slower than waves that propagate on it. In the circle around the point of impact, the water "shoots", so all disturbances or waves are simply washed away and cannot spread. The water looks smooth. Only at the "hydraulic jump", the water has become so slow that behavior of the flow changes. The water level rises abruptly and the water only flows rather than shoots. Waves can move freely in all directions and the water therefore looks much more irregular.

Chapter 7: Hydraulic jump

The overflow itself is “hydraulically controlled”. This means that it only depends on the upstream conditions because the current in the overflow itself is so fast that information about changes in the downstream conditions can’t travel upstream fast enough to have an effect there. Any disturbances are simply flushed away, similarly to a person that is always being brought back down when trying to walk up a downwards running escalator.