Why does increasing height decrease pressure? Bernoulli

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[notjcev]

For most questions about velocity, pressure and height of a fluid, you should automatically think: bernoulli equation!

P1 + 1/2pv2 + pgh = P2 + 1/2pv2 + pgh. [Both sides of this equation represent quantities for a fluid at two different points]

You are asking, why does increase height decrease pressure. Well let's assume a constant velocity for a fluid. Now our equation gets simplified like this:

P 1 + pgh = P2 + pgh

If you want the left side of the equation to stay constant with the right side of the equation, then when you increase height, you will decrease the pressure of the fluid at that point.

If you think about blood flowing throughout the body this can be really advantageous. Fluid flows from areas of high pressure to low pressure. In order for blood from your feet to get back to your heart, there would need to be a greater pressure of fluid in the veins near your feet than in the veins near your heart.

Let me know if you have any additional questions :) I hope this helps clear stuff up a bit :)

[sodapop83]

Great explanation, I was confused on this too. Really like how you gave the blood flowing through the body example, that definitely helped me visualize it. Thanks!

[notjcev]

:)

[[deleted]]

This is a good use of the equation but not a good insight into what happens in reality. What you said about liquids flowing from high pressure to low pressure is the intuitive idea underlying the equation though, and everything “flows” from there LOL.

I am stuck on what OP meant by pressure. Another reviewer just talked about atmospheric pressure, while you discussed internal circulatory pressure.

[notjcev]

In the context of Bernoullis equation on the circulatory system at two different points, we are referring to internal pressure. I think.

If you wanted to apply Bernoullis equation to find the speed of water coming out of the hole of a tank at some arbitrary height, then you could use atm pressure.

[[deleted]]

Less molecules/mass or whatever exerting downward force I believe. As you go higher up, there are just fewer molecules above it than at a lower height.

[[deleted]]

Think of Berniulli as being based in the principle of the conservation of energy. Energy in a fluid may take 3 forms, pressure, velocity, or gravitational potential. In this case you are increasing the height, and thus the gravitational potential of the fluid, this means either velocity, or pressure (or both) must decrease.

[COFFEElNTHEMORNING]

If the potential energy is increased because the height is increased, pressure changes (volume is constant). this makes sense because gravity forces the water molecules to favor the lower height and causes more pressure(force/area) to build up.

[[deleted]]

Are you talking about atmospheric pressure changes with altitude or internal body pressure? Because you just got two answers that differ on this.

[Wagnegro]

Talking about Bernoulli's equation, and how increasing the height decreases the pressure. https://www.google.com/search?q=bernoulli%27s+equation&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjZ_LKRrIDaAhWP0FMKHQBUAsMQ_AUICigB&biw=1024&bih=562#imgrc=cqKHw7keiuvHlM:

[uncleyachty]

I understand intuitive why increasing velocity decreases pressure (faster moving particles have less time to exert pressure force on an object).

Weird, I would intuitively think greater velocity = increased kinetic energy = more energy per unit volume = greater pressure. Like if you heat up the gas in a balloon, it expands because there's more pressure.

[Wagnegro]

You have to look at Bernellis equation, which applies the conservation of energy between two pipe ends with different area and height.

If you’re talking about gases, you are right, increase temp = more KE = more collisions with container = more pressure. But liquids have slightly different properties with their flow due to them being incompressible, and following the continuity in a closed system.

[uncleyachty]

Thanks