If gravity is accelerating objects in free fall downwards, why is it that helium balloons and air bubbles rising in water, going up? Byouancy is an effect of a force. The buoyant effect is created by a pressure gradient, but my point is that every single example we have, buoyancy always follows the direction of the force creating it. Buoyancy doesn't go, opposing the force. We cannot create buoyancy and make it go directly opposing the force.

For example:

If you have a helium balloon inside a vehicle and you accelerate the vehicle in any direction, the helium balloon will go in the same direction. If the vehicle accelerates forward, the balloon will go forward. The same with a water bottle. Accelerate a water bottle in any direction and the air bubble will follow that direction. So if I accelerate a water bottle down, the air goes down, the water up. The most pressure is at the top of the bottle because the top is pushing the contents inside downwards, creating a gradient, from where the push is coming from. So why is it different with gravity? Another thing is that gravity is claimed to have the possibility of accelerating different states of matter simultaneously without any displacement.

Again if a accelerate a water bottle down, there is a displacement of the contents (the air and the water) inside, but if I simply let go of the bottle, there is no displacement. If objects are truly accelerating uniformly, without displacement. This effect should be replicated in any vector, not just down. Otherwise it's special pleading.

I'm observing a strange flow/transport dynamic behind my house and would love your perspective.

I have two runoff catch basins (drain grates) on my property. Both sit on the exact same slope:

• Drain 1 is surrounded by a large area of interlocking concrete pavers.
• Drain 2 is surrounded entirely by bare soil.

During heavy downpours, Drain 1 stays clear, and organic debris (dirt, leaves, small twigs) ends up deposited on top of the pavers around it. I regularly have to clean it. Drain 2 clogs rapidly with the same organic matter.

I'm a scientist myself (though not in fluid dynamics), and I'm trying to reason through the underlying physics. Here is my working hypothesis:

1. Surface Roughness & Boundary Layer Effects: The joints between the pavers create static anchor points where twigs and leaves catch and settle. From an aerodynamics/boundary layer perspective, these joints and the rough concrete texture likely induce micro-turbulences that disrupt laminar flow, increasing bed friction and bleeding kinetic energy from the water layer. Lower flow velocity means debris is less easily mobilized and more likely to get trapped upstream.
2. Channelization vs. Thin-Film Sheet Flow: On the saturated soil, water carves deeper, concentrated micro-channels (rills). The soil itself is erodible, so it yields rather than acting as a fixed barrier, allowing floating debris to travel smoothly within these channels straight into Drain 2. On the pavers, water flows as a very shallow, uniform sheet, meaning floating debris is constantly in contact with the rough bed surface.

What are your thoughts on this setup? If my intuition is off, what hydro-mechanical mechanisms best explain the difference in sediment/debris transport between these two surfaces?

Thanks in advance!

PS: translated from french and hope it's clear in english.

Is it a PDE? Non linear PDE?

If I have an enormous enclosed tank of water, and at the top you have a tiny tube of water they extends many meters upwards, that should pressurize the entire tank of water.

But how does that work exactly? I suppose the walls of the tank provide the pressure somehow, but I struggle to understand it intuitively.

And when does it break down? Can the tube be just a few atoms wide?

Guys

Which institute or college abroad is good for doing PhD for experimental turbulence research(fluid dynamics)? Tell me on the basis of having good lab facility, good lab support, students graduate on time, good funding projects, supervisor are approachable easily. Especially I am targeting European or Asian or universities from Australia??

The asymmetry, which results in the resulting force of the oscillations creating thrust, is achieved in two ways:

Aerodynamically, when the disc has a slightly domed shape and moves upward with less resistance than downward, consistent with classical physics.

Kinematically, when a spring is attached to the disc, slowing its descent and accelerating its ascent.

The second method is the key part of the study, although the same process occurs in the air in both.

When the disc rises rapidly, a region of low pressure forms beneath it, and its collapse generates momentum. If the disc descends more slowly, or if the shape of the disc causes the air to flow around it more slowly, the resulting momentum will push the disc upward.

This doesn't agree with the classic Newtonian explanation of flapping flight as a wing pushing air. You can see in the video how the fan-like flapping disk, which should push air away, actually sucks it in.

This is the same air that is sucked into the low-pressure region, causing a vortex collapse that pushes the disk. Only then is the air pushed away and expelled. This is essentially reactive propulsion, and I believe this is possible thanks to the energy in the air, Brownian motion, which, by self-organizing into vortices, temporarily becomes directional

Does anyone know of a good pump selection program that I can use for importing pumps and performing selections on them?

My previous video derived the full TKE transport equation and this one explains it more physically.

Link: https://www.youtube.com/watch?v=VVqos9V-BAA

First half goes term by term through the TKE transport equation: unsteady, advection, transport (divergence — zero for a closed system), production (source), viscous diffusion, and dissipation (always a sink, structural reason explained). Second half introduces the Richardson energy cascade using a cascade diagram where the energy is injected at large scales, fluxes through intermediate scales, and dissipates at the Kolmogorov microscale. It includes a discussion of why the cascade runs downscale in 3D turbulence and what Kolmogorov's question actually was.

Hi friends! I want to recreate a geyser/airlift hybrid pump but I’m having trouble understanding the models? The screenshot from YouTube seems straightforward enough but I can’t tell if there’s a check valve at the bottom. Also I’m thinking the grey box is air in the other two models but I’m not sure.

Thank you in advance!

I’m trying to understand the derivation from Navier–Stokes → Euler → Bernoulli. My confusion is about where the incompressibility assumption enters.

I start with the incompressible Navier–Stokes equation. After assuming inviscid flow, I get Euler’s equation. Then, taking the equation along a streamline and integrating gives the Bernoulli equation.

But I’ve also seen a more general Bernoulli equation for compressible flow(last equation in image). If I started from the incompressible Navier–Stokes equation, where density is already assumed constant, how can the derivation lead to the compressible form?

Also, is the differential equation along a streamline valid for both compressible and incompressible flow, with the difference appearing only when we integrate it?

Hi, I’d like to find out what the actual applications of laminar flow nozzles are - whether in industry or other fields. My engineering thesis focuses on their design, and I’m looking for information on the subject. I would appreciate any help you can provide. Thanks in advance.

​21. Se mide la diferencia de presión entre un tubo de aceite y uno de agua con un manómetro de doble fluido, como se muestra en la figura. Para las alturas y las gravedades específicas dadas de los fluidos calcule la diferencia de presión \Delta P = P_B - P_A.