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In this video by TAMU Physics & Astronomy titled "Eggs can support A LOT of weight!": https://www.youtube.com/shorts/a7JvE-fGrgg?feature=share

The teacher first grabs an egg and places it on the side and then puts a 2kg weight on top. The egg immediately breaks. They then grab three eggs on their sides and puts a large baking tray on top. The teacher then adds weight after weight until a total of 8kg is on top of the 3 eggs. The eggs survive for a while and then eventually break (after presumably a few minutes).

We see the teacher demonstrate that a single egg will break with a 2kg weight on top, but 3 eggs can support 8kg (plus 0.1 or so from the tray), which is 2.7kg per egg.

What physics principle is this demonstrating? How does it work?

My only thoughts are that it's because the weight is sharper and cracks the egg more easily. Or maybe something to do with rotating since the first egg is not balanced, but it doesn't look that way and the experiment wouldn't make sense if that were the case.

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  • $\begingroup$ How are the three eggs configured? Exactly how is the weight placed? $\endgroup$
    – WillO
    Nov 25, 2023 at 15:12
  • $\begingroup$ Minor comment to the post (v2): Please consider to mention explicitly author, title, etc. of link, so it is possible to reconstruct link in case of link rot. $\endgroup$
    – Qmechanic
    Nov 25, 2023 at 15:56
  • $\begingroup$ Some eggs are stronger than others. Perhaps it was luck. $\endgroup$
    – mmesser314
    Nov 25, 2023 at 17:56
  • $\begingroup$ repetition of experiments is important if you want to infer something $\endgroup$
    – basics
    Nov 25, 2023 at 18:57

2 Answers 2

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With a fracture process the fracturing is usually caused by a local concentration of stress, that is there is some small region where a lot of force is concentrated in a small area and the resulting stress exceeds the strength of the material.

In the first experiment the metal weight is placed directly on the egg:

Single egg

Metal is much harder than eggshell so if there is any unevenness on the surface of the metal that will concentrate the weight at that point. Also, though we cannot see it in this photo, the weight has a hole in the centre and the sharp edges of the hole will be pressing on the egg.

By contrast in the second experiment a plastic tray is placed on the eggs and the weights are paced on the tray:

Three eggs

My guess is that the plastic of the tray is softer than the eggshell so it deforms and spreads the weight evenly over the eggs. That means the stress is lower and hence a higher weight per egg can be supported.

To make the experiment fairer the same plastic tray would need to be used in the single egg experiment.

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  • $\begingroup$ Thanks, I feel like the teacher is pretty misleading in this experiment then. $\endgroup$
    – Aequitas
    Nov 26, 2023 at 11:53
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    $\begingroup$ @Aequitas I agree. It's not a good video. $\endgroup$ Nov 26, 2023 at 11:54
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Because the pressure changes and the weight is distributed to each egg.What causes fracture or any other plastic deformation is pressure not force.

Pressure $P$ is related to force $F$ by this formula: $P = \frac{F}{A}$.There is a $P_{critical}$ under which the object is deformed.

If $P_{critical}$ remains the same(logical since each egg is made of the same material)by making $A$ bigger $F_{critical}$ also becomes bigger.

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