Boats with same volume but different shape

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Boats with same volume but different shape

Postby nissan » Wed Feb 29, 2012 1:33 pm

hello ,

We made boats with same volume but different shapes. We made rectangular, square, cylinder and cone. The cylinder one took more wt. than any other shape.For the same shape & volume, we also made taller kind of shapes and shallower shapes.. I can see same kind of pattern for taller and shallower shapes,
in both kinds, the cylinder shape took more weight. How can explain the results on why that shape took more weight?
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Re: Boats with same volume but different shape

Postby edneu3 » Thu Mar 01, 2012 1:26 pm

Hmmm. This becomes difficult to explain, but physics still applies here.

The amount of weight any buoyant object can support is equal to the weight of the water it displaces. So if solid A displaces the same amount of water as solid B, they both support the same weight. So, if all your solids have the same volume, they should support the same weight. This is your dilemma.

I think the key is understanding what criteria you used to establish how much weight the boat held. Was it based on the boat sinking from taking on too much water, or some sort of failure?

I'll assume it was based on the boat sinking. Then I need to understand how were your boats constructed? For instance, did the cylinder have one of the circular ends missing so that it stood up in the water, or did you cut away one of the sides so it looked more like a canoe? Whichever way you constructed your boat will make a big difference in how much water it can displace, that is how much weight it can hold, before sinking.

Perhaps if you could tell me more I can help you come up with a better understanding of your observations.

Good luck.
Ed Neu
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Re: Boats with same volume but different shape

Postby nissan » Fri Mar 02, 2012 9:38 am

Thanks for replying..

I think unless we see how I built its hard to explain i think.. but no cylinder is not built like a canoe..

Well.. My confusion is depending on the shape like for cone.. if I calculate the density.. Mass it takes by volume(which is same as other volumes).. it sinks even if the density is less than 1. But the rule is if density is less than water, it should float. How canw e explain this? Or Am I doing something wrong in constructing.. I am not sure how to proceed with the experiment from here
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Re: Boats with same volume but different shape

Postby edneu3 » Fri Mar 02, 2012 10:12 am

As you have observed, the physics is very straight forward and basic here. If the density of any solid object is less than that of water it will float.

The only thing I can think of is that perhaps you are computing the volume of your solids incorrectly. What formula are you using for each solid?
Ed Neu
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Re: Boats with same volume but different shape

Postby nissan » Fri Mar 02, 2012 10:55 am

I am using formulas from this site to build.
http://www.grc.nasa.gov/WWW/BGH/volume.html
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Re: Boats with same volume but different shape

Postby edneu3 » Fri Mar 02, 2012 11:29 am

These are certainly the correct formulas.

If you like, I'm willing to serve as a checker for your work. If you send me the dimensions of each of your solids, and your computed volumes, I can check your results.
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