# How can we intuitively understand the idea that when the velocity of fluid increases, the pressure of fluid decreases?

In the above example image Example 1, I understand the reason why the pressure will decrease when the velocity increases. The reason is given as follows by Richard Feynman:

The speed $$v_2$$ must certainly exceed $$v_1$$ to get the same amount of water through the narrower tube. So the water accelerates in going from the wide to the narrow part. The force that gives this acceleration comes from the drop in pressure.

But, I fail to understand how on increasing the velocity the pressure decreases, in every case.

For example, Richard Feynmann also gives the following Example 2:

Example 2:

Have you ever held two pieces of paper close together and tried to blow them apart? Try it! They come together. The reason, of course, is that the air has a higher speed going through the constricted space between the sheets than it does when it gets outside. The pressure between the sheets is lower than atmospheric pressure, so they come together rather than separating.

How do we understand this phenomenon in Example 2 just with the help of Newton's Laws, forces, energy conservation, etc. as explained in Example 1?

Can we explain every case with such a detail of forces as explained in the first Example 1?

In summary, I fail to understand this phenomenon intuitively.

Could someone explain it to me by taking 5 different examples in different contexts, so that we understand it intuitively, why it so happens?

Currently, in most cases it seems kind of magical that when velocity in a fluid increases, the pressure decreases.

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– Chris
Dec 15, 2019 at 2:13
• Bernoullis equation is basically an energy balance. When the velocity increases the kinetic energy increases so if the potential $$\rho g h$$ stays the same then the pressure must drop Dec 16, 2019 at 5:04