I saw a video describing how the ‘mystery of Rupert’s drops is revealed,’ and I did not understand any of it. They said something about the drop part and it’s distribution of stress: compression on the surface, tension in the interior. Ok? I have no idea what that means lmao, anyway if anyone could enlighten me on this I’d be quite thankful!
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Imagine the glass molecules as a bunch of people holding arms in a formation. In a normal bead of glass, they are just loosely connected to all the people around them. Rupert’s drops are a bead of glass where most are instead pushing against all of the people around them, while the outer edges are pulling on their neighbors. Because they are pushing against each other instead of just hanging on, they keep their formation with a ton more strength. The biggest drawback is that if one person in the formation trips, then everybody around them falls into that hole because they are still pushing towards them.
We often separate material strength into strength during tension and compression. If you imagine a rope you can tension it quite a lot without in breaking but if you try to compress it then it will just bend away so you can not push something with a rope, only pull something. On the other end of the scale a pile of rocks is very poor in tension as it will just fall apart when tensioned, however you can compress it a lot before it will actually yield so it can support quite a lot of weight.
Glass is very good in tension, but very poor in compression. It is very hard to exploit its good properties in tension though because if it starts to bend then one side will be in tension and the other in compression. And since it does not handle the compression it will just shatter. However in a Prince Rupert’s drop the outside of the glass cools first and when the inside cools it contracts putting the already cool outside glass in tension. This is usually referred to pre-tensioning and is done deliberately for large structures like bridges to change their properties. As the glass is already in tension if you try to bend it then you will not compress it but just releave the tension. You have to apply a lot of force to it in order to releave all the tension and get it to compress.
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