Let's say I have a solid shape - a sphere, a cylinder, I don't know if it matters - and I place that solid in a container of water. The forces on the shape consist of gravity and buoyancy (due to hydrostatic pressure).

Then I turn on some aerators and form a steady stream of bubbles in the water. What sorts of forces develop on the solid once the bubbles contact the solid?

Empirically, I know people use bubblers to reduce the impact of Olympic divers hitting the water when they mess up their dives. I think this is because the bubbles result in a reduction in the fluid density, which slows the acceleration of the diver once they impact the (now gassy) water. So we know there will be a change in the buoyant force.

I also know there will be some surface tension component (no idea how to calculate or approximate it). And I think there will be some momentum interchange as the gas bubbles impact the solid. But is the net force upwards, downwards, or is it balanced?

To illustrate what I'm asking... imagine I have a very large bubble, maybe the size of the solid or larger. And it's moving upwards quite quickly. If it were a solid object, the collision would be understandable to me. But it's a gas that has to displace the liquid between itself and the solid prior to colliding with the solid object. So how does that change the nature of the collision? And if the bubbles are quite small (and I can treat the fluid as a continuum), is the collision model still valid?


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