eggshells

[fpegr]

I would like to know which eggshell suports more weight the pointed dome or the rounded dome.

[phi-unit]

Hi,

Your idea sounds very interesting but I am somewhat unsure of what you are trying to do for your experiment. It seems as if you are going to test different shapes of eggs in order to see which shape will support the most weight.

To get you started you should first read the sciencebuddies Fallen Arches project description. It will provide a description and discussion of how to test an eggshells strength. Here is the link: https://www.sciencebuddies.org/science- ... p021.shtml

In your experiment you can probably use the same set-up but vary the egg shape to investigate how different shapes(of eggshells) affect their load-bearing capacity.

Please feel free to post a reply with any further questions you may have

phi-unit

[fpegr]

Thanks a lot for the information, we checked the web site you mention, in fact that's where we got the idea for the Science Fair Project.

We tried to check the Variation mentioned on the web site:
Variations
•In this experiment, you broke the pointy end of the egg, and measured the strength of the arch made from the larger diameter curve. What do you think the results would be if you instead broke the larger end of the egg, and tested the strength of the "pointy" arch?

We thought the pointed end would support more weight than the rouded end but we got nothing conclusive. So we wonder if our initial assessment was wrong. Do you have any idea?

[Craig_Bridge]

We thought the pointed end would support more weight than the rouded end but we got nothing conclusive. So we wonder if our initial assessment was wrong. Do you have any idea?

When it comes to science, it really doesn't matter what anybody thinks or proposes as a hypothesis. It doesn't even matter if your hypothesis is wrong. What matters is if people think you used a valid technique to prove or disprove your hypothesis. Your results (observations) are what they are. What do you mean by inconclusive?

How many samples of each did you try? Did you inspect the samples with a light and magnifying glass to determine if there were any visible cracks before you ran the crush test? If you plot the result of each sample on a scatter graph using different colors or symbols for the pointy end and rounded end, do the results tend to overlap completely or only partially between the two types?

If your results overlap and you can't tell if the overlap is complete or partial, then it is usually best to run additional samples. Scientists often use some mathmatical statistical analysis formulas to determine statistical significance of their data and to determine if they have tested enough samples; however, this would definitely be beyond your grade level.

As an engineer, I can tell you that the vertical force it takes to break the cut edge of the egg will change with the angle the edge makes with the bottom plate of your fixture. All other things being equal, the shallower (flatter) the angle, the less force it will take to crush it. To be a fair test, you need to pick sample sizes from both ends that make approximately the same angle with the bottem plate.

[fpegr]

I really appreciate your answer. We did consider that the bottom part attached to the plate would tend to tear open so we placed masking tape around it, so the eggshell would not break open. We tested each shape three times (probably not enough) and we got these results:

Supported weight (Kg)

Flatted: 5.25, 6.50,7.75 average: 6.5
Rounded: 12.95, 17.15, 14.90 average: 15.0
Pointed: 8.55, 14.15, 16.80 average: 13.17

Eggs always crashed on top.

We will repeat each shell more times.
Thank you.

[Craig_Bridge]

We did consider that the bottom part attached to the plate would tend to tear open so we placed masking tape around it, so the eggshell would not break open.

I hope that you realize that by adding an application of masking tape to the eggshell samples you are no longer testing just the eggshell structure. You are testing an adhesive bond to eggshell, the eggshell, the masking tape, and any geometric differences in the application of the masking tape to the eggshell samples.

This application of masking tape may cause differences in the failure mechanisms of your samples.

Just looking at your raw data, the 8.55 pointed sample is an outlying data point.

I was curious what some statistical analysis considering the {pointed}, {rounded}, and {{pointed}+{rounded}} populations would tell me so I put the numbers in an Excell spread sheet. The only additional insight it provided was this 8.55 pointed sample was a far outlying point in both the {pointed} and {{pointed}+{rounded}} populations. This makes it suspicious as having a different failure mechanism than the other samples.

We tested each shape three times (probably not enough)

Given you have a far outlying point that comprises 1/3 your pointed test sample population, you definitely don't have a big enough population to draw conculsions. You need to run at least 3 more samples of pointed and rounded to have enough data to predict how many samples you might need to determine statistical significance or insignificance. Something that is well above your grade level. Post back any additional test results and I'll be glad to put them in a spread sheet and analyze it for you.

The question that has to be answered was that 8.55 test sample a rare abnormality or does the population have a broader variation than is being represented by the other samples.

[ChrisG]

Hi fpegr,
Congrats on successfully collecting those data. I'm glad to see that you've been getting some very helpful advice in this thread. From your answers, I was not sure if you are a parent or student, and I was not clear about the grade level of the student(s) involved. Because math and science skills vary widely over the grades K-5 included in this forum, could you please tell us what is the grade level of students doing this project and maybe a little bit about what sort of math & science skills they are currently studying?

If the students working on this project have not been exposed to the math needed to begin to understand statistics, a graphical representation of the data is an useful method for qualitative interpretation. From a graph of the data, one could see that the rounded and pointed shells give similar results and that both fall outside the range of results from the trials using the flattened side of the egg shell. For more advanced students, if there is time to run additional trials and sufficient knowledge/experience to perform statistical analyses, those efforts would certainly be worthwhile.

When interpreting your results, you might also be interested to read about the factors that affect egg shell thickness and strength:
http://ag.ansc.purdue.edu/poultry/multi ... ebeck1.htm (second paragraph)
http://www.rirdc.gov.au/pub/shortreps/sr75/sr75.html (see fig. 3, fig. 5)
A search for "egg shell quality" will provide many other useful web pages.

Best regards,
Chris

[MelissaB]

A side note I can't help but add is that different birds produce eggs that are shaped differently--ostrich eggs are almost completely spherical, for example, whereas birds that nest on cliffs have very pointed eggs so (we think) the eggs don't roll off. It might be something you could bring up in your discussion!

[Eric]

My daughter and I found that eggshells cut in half the long way hold less weight than eggshells cut in half the short way. I would appreciate any suggestions as to why this might be the case or where we can look to try to understand the answer. Thank you.

[Craig_Bridge]

My daughter and I found that eggshells cut in half the long way hold less weight than eggshells cut in half the short way. I would appreciate any suggestions as to why this might be the case or where we can look to try to understand the answer. Thank you.

There are probably several factors involved. The perimeter of the egg cut in half the short way is a circle and is shorter than the perimeter of the egg cut in half the long way which is an "egg" shaped oval.
1) The longer this perimeter, the more stress fractures it likely has from the cutting operation.
2) The more uniform smaller radius curve of the circle spreads the forces more uniformly than the variable radius curves of the "egg" shaped oval. The longer radius portions are weaker.
3) The structure is only as strong as its weakest part.

You can demonstrate the second factor by holding a piece of paper upright on one edge and pushing down on the top edge. The paper will bend more easily the farther away from where you are holding it. If you roll the same piece of paper and tape the top to the bottom to make a cylinder, then stand it up, you can probably support a paper plate with some weight on top of it before it crumples. Lay the paper cylinder on its side and it will flatten out quickly with very little weight. You can also cut another piece of paper in half and make another cylinder of the same length but smaller diameter (tighter radius) and compare how much force is required to crush the two cylinders. You should find that the smaller diameter cylinder will support more weight as long as the proportions of the length to diameter don't get large enough that it tips over instead of crumpling.

You can demonstrate the third factor by making some tears along the ends of another paper cylinder and observing that instead of crushing it can tear and split and fail with less weight.

Creating a finite element structural analysis model of an egg shell is a sufficiently complex task that most structural engineers would have trouble getting anywhere close without many iterations. I'm sure my over simplified paper models won't come close to answering all of the factors.

[Eric]

Dear Craig:

Thank you for your explanation. With regard to your point 2, why is it that the longer parts of the eggshell are weaker? Is there a way of explaining it so that my 7-year-old and I could understand? Thank you again.

Eric

[Craig_Bridge]

With regard to your point 2, why is it that the longer parts of the eggshell are weaker? Is there a way of explaining it so that my 7-year-old and I could understand?

I don't think anybody can really answer "why" any observed physical behavior "is". The most advanced degrees in science and engineering are called "Doctor of Philosophy" because people spend a lot of time thinking about these things and typically come up with mathmatical models that attempt to predict and match observed behaviors. If I were to attempt to try and explain one of these mathmatical models and how it predicts the observed behavior, then I'm not really telling you anything about the "why" an observed behavior "is". If one has enough analytical math skills to understand the mathmatical model, thinking about it might provide some insite to predict other behaviors, but it isn't really going to answer the "why".

I tried to give you some simple experiments that you could do with a piece of paper and forming it into a cylinder in order to make some additional physical observations using something with a simpler form than half an egg shell so you both might observe how form can affect crush strength.

Another thing you might try is to experiment with basket weaving to learn about how structural strength in a woven form behaves. To model the egg, you will want to choose to weave with a wide frond and not sticks which would act as beams instead of flat material. You could also use strips of construction paper to weave with. I think you will find that pushing against the sides along the long axis will cause the long sides to deform first and pushing against the longer sides on the short axis will also first deform the longer sides. If you experiment with a loose weave that is free to slip, you might be able to observe the slippages and observe how external forces translate into forces around the formed surfaces.

It is funny how children of anchient peoples developed a better intrisic feel for structure and form from doing some day to day tasks than modern childern.