The Bernoulli's pri...
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The Bernoulli's principle can be found in the electric current, too  


Mitko Gorgiev
Member Admin
Joined: 3 years ago
Posts: 36
26/10/2019 7:38 am  

When a body moves through space filled with air, then higher pressure is created in front of it, while lower pressure/depressure behind it. The higher pressure is plus, the lower pressure is minus. I use to call this a ‘principle of an arrow’ (− >—> +).

The greater the velocity of the body is, the stronger is the plus in front of it as well as the minus behind it. This principle can be found in many things, among others also in the so-called “Bernoulli’s principle”.

What is “Bernoulli’s principle” in its basic form? The picture below shows it. The water flows through a wider pipe and then through a narrower pipe. The velocity of the water increases in the narrower pipe. As a result, the water column over it is lower than over the wider pipe.

Why is that so? The water columns over the pipes could be imagined as side-tails of the water-body. Since the velocity of the water is greater in the narrower pipe, a stronger minus (i.e. stronger depressure) appears in its tail than in the tail of the wider pipe, thus the air-pressure from above lowers the water column over the narrower pipe more.

At the same time a stronger plus appears at the front part of the narrower pipe. Everyone knows that the water-jet which comes out of a pipe reaches farther if we narrow the pipe. That happens because higher pressure occurs in the front part.

So, higher pressure at the plus-side (the front-side), lower pressure at the minus- side (the back-side).
Please watch this YouTube video Why does water spray farther when the garden hose is narrow?

The principle of an arrow can also be seen with light. The archetype of this pattern (≈ principle) is the flame of a candle or a cigarette lighter. A violet-blue color appears on the back and a yellow-red color on the front of this fiery arrow. (The violet/blue/cyan are minus-colors, the yellow/orange/red are plus-colors. In the past they have been called cold and warm colors, but now I additionally call them minus and plus-colors. )

(image borrowed from, the arrow is added by me)

And this pattern can be found wherever colors appear. Look at, for example, these colors obtained from a light source (it is in the middle) with the help of a diffraction grating (image borrowed from Except Integrated Sustainability. The arrows are added by me.).

A manifestation of the Bernoulli’s principle can be seen also with another fluid, and that is electricity. If we make a series connection of two wires of same metal, but of different cross-sectional areas, place them on a table in straight south-north direction, under each piece place a compass (the compasses are identical) and then connect this assembly to a battery, we will notice that the deflections of the needles are different. The magnetic needle under the thinner wire makes greater deflection than the needle under the thicker wire (more about this you can find here

Mitko Gorgiev
Member Admin
Joined: 3 years ago
Posts: 36
27/01/2021 12:04 pm  

At the beginning of this article I have explained that when a body is moving through space filled with air, then higher pressure is created in front of it, while lower pressure behind it. 

The movement of the body is actually braked from two sides. At the front side there is a higher pressure which pushes the body back and thus slows it down. At the back side there is a lower pressure which pulls the body back and thus slows it down, too (figure below). The faster the body is moving, the higher is the pressure in front of it, which pushes the body back stronger. At the same time the lower is pressure behind it, which pulls the body back stronger.

In few words: the greater the velocity of the body is, the greater is the force of opposition to its movement.

The principle of an arrow can be found also in another thing.

Let’s consider the following: we hold a straight thick copper tube vertically and let fall through it a strong and long cylindrical neodymium magnet with its plus-pole ahead. The diameter of the magnet is only slightly smaller than that of the tube. We notice that the magnet in the tube is falling much slower than it is falling outside the tube. We conclude that in the metal of the tube is evoked an electric current which delays the fall of the magnet. This delay happens from two sides. While the magnet is falling through the tube, its lower end at every moment is entering the remaining part of the tube, whereas the upper end is leaving the already traversed part. Both effects must slow down the fall; for, if the one effect slows it down and the other accelerates it, then these two effects would cancel each other out and the magnet would fall with the normal speed. Hence, when the magnet is falling down with its plus-pole ahead, it evokes in the part of the tube - which is lower down - the EM-forces whose M-segments are oriented with their plus-poles upwards, thus repelling the magnet; however, in the part of the tube which is higher up than the magnet (where its minus-pole is), the EM-forces are evoked in the metal with their plus-poles of the M-segments oriented downwards, therefore attracting the magnet (in relation to this please see my articles cited at the end). The arrows in the gray rings (figure below) refer to the inner side of the tube, thus I should have drawn them dashed.

We have here a very similar picture as above with the body moving through the air. The differences are the following: 1) in the first case the opposition is caused by the air, which is a material thing; in the second case the opposition is caused by the M-forces, which are immaterial; 2) in the first case the air is already there; in the second case the magnet creates the opposition by itself, that is, its movement evokes in the tube the EM-forces, which in turn offer the opposition to the magnet’s movement.

See also:

What is an electrical current?

What is electromagnetic induction?

Here is a video with the falling magnet.