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Name: Gary
Status: Educator
Grade: 6-8
Location: WI
Country: United States
Date: July 2006


Question:
When building a large-scale public aquarium (perhaps to be installed in our school), is there a formula used to determine thickness of glass based on pounds of water pressure?



Replies:
Hi Gerry,

The short answer is "No; it just is not that simple". While determining the pressure that water exerts on a glass wall is pretty simple, determining the glass thickness needed to resist this pressure is not quite so simple. The glass will be subjected to bending stress as the pressure tries to force it outward. The actual amount of stress depends on the unsupported area of glass. The glass wall or "window" is fixed and sealed at its edges, but unsupported over its area. The larger the window is, the greater the bending stress that results. If you think about it, this is actually fairly clear (must stop with those puns!). Let us say that the water is deep enough to exert an average pressure a pressure of 50 pounds per square foot against the window. The larger the window, the greater number of square feet of glass is holding back the pressure. If we have one window that is (let us say) 10 square feet in area, then there will be a total force of 500 pounds forcing the glass outward. But suppose we want to use a window that is 100 square feet in area. In that case, there will be a total force on the glass of 5000 pounds. Obviously the larger window will need to be thicker to resist the greater force.

Regards,

Bob Wilson.



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