|MadSci Network: Engineering|
Hi Ethan, You've asked a very good question, and it shows that you have a pretty solid understanding of how vacuum and atmospheric pressure behave. The short answer to your question is that the glass jar didn't break because it was strong enough to withstand the kind of pressure that Boyle put on it. Why the glass was strong enough is a bit more complicated, but still pretty cool. Glass typically has a tensile strength of about 2000 to 25000 pounds per square inch (psi). The compr essive strength is normally much higher than that. Atmospheric pressure (On average, at sea level, at room temperature) is 14.7 psi (101.3 kPa or 760 mmHg). So at full vacuum, the jar would have 15 psi compressing in on it from all directions, which is considerably less than the pressure needed to crush it. Additionally, the air pump used, (built by Hooke, who also did a lot of cool science stuff) probably wasn't able to suck out all of the air from the jar. Even modern vacuum pumps like Turbopumps and Cryopumps can't suck ALL of the air out of a container... In order to crush (also known as "implode" because it catastrophically fails inward) a glass jar using vacuum, (I highly recommend AGAINST doing this...) you'd have to do one or more of the following: 1) Make the walls of the jar very very thin. 2) Add scratches, chips, and dents to weaken the glass. 3) Apply extra atmospheric pressure. 4) Apply a very high vacuum in the jar. 5) Make the jar non-cylindrical. (Cylin drical structures are very strong because of their shape. To see this better, get a two liter soda ("Pop" for most people in your region...) bottle, and try to collapse it by sucking the air out of it. You'll notice three things: 1) it collapses by having the sides cave in (also known as "buckling"), 2) it's easier to do if you dent or bend the sides with your hands before pulling the air out of it, and 3) it's hard on your lungs...) I hope this helps! Let us know if you have any more questions. Jeff Yap Mad Scientist Cool sites: Encyclopaedia Britannica Online Glass Encyclopedia - American Glass
Try the links in the MadSci Library for more information on Engineering.