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How can I displace the maximum amount of water in a bucket?

  1. Feb 26, 2015 #1
    The scenario involves dropping something into a bucket of water. I'm trying to do an experiment where I have to figure out a relationship between the amount of water that leaves the bucket and a certain variable of the object that is dropped.

    I'm wondering what could maximize the water that leaves the bucket. The waterlevel will be 4 cm below the height of the bucket. The object will be dropped 1 meter above the water level.

    To keep things simple, nothing that involves any moving parts/suction/nuclear/electrical interactions. I'd like to know what kind of variables are involved in calculating the amount of water that can be splashed out of the bucket and how to maximize them.
  2. jcsd
  3. Feb 26, 2015 #2
    Gosh, that's not an easy question. Splashing is a complex process. For this you need an expert in fluid dynamics- or a lot of trial & error:wink:.
  4. Feb 26, 2015 #3


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    The rules aren't very clear. Could you use the bucket as a mould to cast a lump of concrete then "drop" that in?
  5. Feb 27, 2015 #4
    Hey, sorry about the slow reply.

    So, basically the rules are that the object which displaces the water must weigh less than the amount of water displaced. Next, the object cannot have any additional energy (apart from the gravitational potential energy) stored that can interact and displace water. It cannot tip over the bucket or significantly damage it (eg. make a hole) in any way.
  6. Feb 27, 2015 #5
    I guess the most challenging part of the problem is to figure out parameters of the generated wave due to object impact.
  7. Feb 27, 2015 #6
    Drop in a stick of dynamite ( fuse lit of course ) . That should have a maximum effect for you.
  8. Feb 27, 2015 #7


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    One meter drop? Cylindrical bucket? Or frustum of a cone? Someone's already suggested casting concrete --- how about something less dense than water?
  9. Feb 27, 2015 #8


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    I think you need to find a resonance as the water is sloshing around. I think you can treat the system as a Helmholtz Resonator You need the gap round the side of the object (piston) to tune with the mass. There's a simpler electrical equivalent with an RLC circuit.

    But of course, a piston which fits the bucket perfectly is a sure fire solution. The above only applies of you have imposed limits.
  10. Feb 27, 2015 #9
    To maximize the splash you need to increase the force of the object being dropped by:-
    1) Increasing the mass
    2) Increasing the acceleration by throwing harder

    You also need to increase the surface area of the object as to cover the maximum surface of the water.

    I hope I helped you. Do ask me if you got some doubts :)
  11. Feb 27, 2015 #10


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    We are told that the drop is from 1 meter height. To make a fair test, an obvious assumption would be that the mass is also fixed, though this is not explicitly stated.

    The difficulty with simply increasing surface area is that this may to result in a horizontal splash. We are told that the bucket has sides that rise 4 cm above the water's surface. These would serve to prevent horizontal splashes from escaping. So, while it is true that one would want to avoid an overly compact object (do not use a neutronium sphere), using a thin horizontal plate may not serve well either.

    One possibility would be a shape consisting of a number of tapered and angled tubes, large at the bottom and narrow at the top.
  12. Feb 28, 2015 #11
    I don't know why, but I picture a stratified, hyperbolic shape. I.e., cork or styrofoam (easily shaped) for the first, hyperbolic portion of the penetrator, followed by iron or lead disks. Overall, the object could weigh less than the water displaced.
    The idea is to create a wave with the lightweight, hyperbolic portion. The heavy disks supply the energy. A hyperbola may not generate the best results. A parabolic shape might be tried, along with many others. The benefit of this approach is that different shapes are easy and cheap to produce. The heavy disk(s) behind them may also be varied without too much trouble or expense.
    Another possible reason behind this approach... "Dropped from one meter." Is that the bottom of the object? This approach places the heavy part higher and allowing more energy. A really clever use of this might be to allow the tip of the penetrator to be crushed upon impact at the bottom.

    Try inverting it as well. Let the heavy disk(s) enter first and follow with the lightweight, shaped portion. Not only may one possibly make the biggest splash, one may also show experimental results from the various shapes and weights that led to that big splash. Just a little brainstorming on my part...
  13. Mar 4, 2015 #12
    If you want the maximum difference between the weight of the object and the weight of the water displaced then you should try to keep the object as light as possible. You should also try to keep the surface as flat as possible. Perhaps try a flat lightweight styrofoam plate? That way, even though the object is light and won't displace as much water as a heavy object, the object itself weighs almost nothing so you get a greater difference.

    Source: third year engineering student
  14. Mar 4, 2015 #13
    I like the dynamite idea..... although I'm sure you probably want the bucket in one piece at the end of the experiment. That would also rule out piercing the bottom of the bucket with a spike and letting the water drain out.

    The cast of concrete probably wouldn't work. Assuming the alignment is perfect, even with a slightly inclined side of the bucket, there will be a point at which the concrete will end up blocking the escape of the water and merely compressing the water beneath it. I bring this up because you specifically said splashing the water out. Assuming the concrete doesn't get stuck against the sides of the bucket, beyond the point where the water yet to be displaced can near fully arrest the fall of the concrete the displacement will simply be overflow or oozing. So it may eventually displace the full bucket of water, but at the cost of time.
    I think your best best is a heavy cylinder of a diameter smaller than that of the bucket, but a height greater than the walls of the bucket. That should allow most of the water to be displaced at a greater rate, and the height will help prevent anything from falling back into the bucket. A conical shape may work better, but for that you'd have to talk to a fluid dynamics type.
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