87 upvotes, 2 direct replies (showing 2)
View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
I’m guessing this is a physics or fluid dynamics question - When shaking a closed container with a fluid inside (say water) to clean the inside of said container, is there an optimal amount of fluid to clean it?
I ask as I notice when shaking a closed container at 100% full with water it doesn’t feel like it’s moving/swashing inside, but when it’s 1% full it doesn’t seem to have enough mass/movement/kinetic energy inside to clean it.
Apologies for the really crude and maybe confusing question.
I can imagine there are a lot of variables to this, like the viscosity of the fluid, the particle material and size of what you’re cleaning off (E.g cohesive and non-cohesive particles). The container dimensions. The frequency and amplitude of the “shaking”. Or! I could be over thinking this.
Comment by SonOfOnett at 20/07/2022 at 20:55 UTC
30 upvotes, 1 direct replies
I love this question, but I agree that any answer to the question depends on precisely defining a ton of variables: there’s not going to be a general answer of, say, 25% for any shaped container, viscosity, shaking frequency etc
Potential Approaches:
Simulation:
You could program a physics model for a specific condition and try it out. Maybe google a bit to see if anyone has done anything like this before.
Experiment:
Run a real test and report results
Analysis:
Try learning a bit about random walks. Start with collision probability in 1 dimension then 2 then 3. Seems like a really nasty analysis but you might get some intuition from looking into this
Comment by BottleONoobSauce at 20/07/2022 at 22:48 UTC
4 upvotes, 1 direct replies
When you're shaking a closed container that's 100% full, the water molecules ***are*** moving around, it's just that you cannot ***see*** their motion. With a less full container, you feel and hear the swashing/movement when you shake it because the pockets of air serve as a medium in which sound can travel through.
Water serves to dissolve water-soluble compounds that you want to get rid of when you're cleaning, but there is a limit to how much *stuff* can be dissolved in a certain volume of water.
Consider a dirty wine glass left out overnight: would you rather clean the glass with 1 drop of water, or 1 cup of water? Of course one cup. Why not one drop? Because it will quickly become saturated with your leftover wine residue, and no matter how much you swash it around or shake it, your wine glass will not become clean, because one drop of water cannot solvate all of the residue that's within the cup. This is an extreme example as nobody would choose to clean anything with only one drop of water, but demonstrates that when you are trying to dissolve things (as you are doing when you are washing clothes or your dishes), more water is always better.
Another intuitive example is: if you drop a very small drop of food dye in a container that's full of water, close the lid, and start swishing it around, you will see that very quickly, the entire container becomes a different color, even though you won't hear much swashing around. This demonstrates that the water molecules are indeed moving around, and would not be the case if they were not moving.
Note that just because more water is always more effective, there is a point of diminishing returns. Please do not attempt to clean your dishes using a swimming pool's worth of water.