Vacuum doesn't exert a force. The gases released do.

You can look at this from a force diagram. Having a vacuum behind the shell just means there isn't gas pushing on the shell. Adding a gas does push on the shell.

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Given the water density and weight, what would happen if a person skydived into clouds?

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It depends mostly on the topology of the area around the river that floods. If the area that floods is very wide and flat the average flow velocity will stay nearly the smae as pre flood, where as if the river is in a narrow steep walled valley the flow velocity will increase.

Wouldn’t the slope of the region also play in a role in the velocity?

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It's an interesting question, but unfortunately one that's not going to have a definitive or single answer. The short version is that you expect a lot of variability in flow velocity during a flood where the velocity in any given area (or with depth) will depend on the discharge (i.e., the volume of water moving through the system) but also critically the "roughness" of the contacted area. For a bit of a treatment on this from a fluid dynamics perspective, you could consider things like Pang, 1998. Roughness always play a role in flow velocity in rivers, but compared to periods where the flow is constrained below "bankfull width", during floods roughness can vary a lot both from natural elements (i.e., as flow moves up the walls of the bank and potentially over natural/manmade levees) but also from flows encountering all sorts of "objects", i.e., trees, other vegetation, and a whole host of things in the built environment (roads, poles, houses, etc.). You can see some of the extreme variations in relationships between depth and velocity estimated from modeling flood flows in built environments in papers like Kreibich et al, 2009. Another aspect of this is that this actually something that's pretty challenging to measure because floods are not necessarily the easiest or safest time to go measure flow velocity (and it may often destroy or damage more autonomous instrumentation deployed to track flow velocity). This is discussed a bit in papers like Tauro et al., 2016, which is attempting to use image techniques to estimate flow velocities during floods. This highlights some of the challenges in empirical measures of flood velocities, but also demonstrates the significant spatial variability in velocities during floods (as estimated from their techniques).

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We are living on the cool surface of a hot planet. Is there any practical reasons why geothermal isn't the answer to most of our energy needs? What I'm asking is there a reason that geothermal has gotten so little funding over things like fusion.

All the energy we could want is only 10-20km away.

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What's the best evidence against flat earth?

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>IS pushing the shell

By a negliglible amount. There are actual range-boosted shells with rocket motors which gain significant thrust from the shells actually accelerated in flight.

Base-bleed is not that and for simplicities sake these shells aren't said to be propelled by it, they just have less drag.

I think their point was that the purpose wasn't propulsion, but a reduction in drag. If you look at the momentum imparted by the gas released it will be much smaller than the decrease in momentum caused by drag if the gas weren't there.

Ya or why a balloon falls slower than a bowling ball in atmosphere when both are smooth and round.

Sounds counterintuitive but makes perfect sense, thank you. It's why downhill skiers are faster when they weigh more.

No though you will have the same force acting on a heavier bullet, so the drag will affect the bullet less. That is why heavier bullets have higher ballistic coefficients.

“Filling the empty void with gases” IS pushing the shell. It might not have a net positive acceleration, but it’s like pushing a car that’s out of gas - you’re still pushing even though it’s not accelerating.