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Container Shape and Pressure
Name: Billy
Status: Student
Grade: 6-8
Location: DC
Country: United States
Date: September 2008
Question:
How does the shape of a disposable water
bottle (Dasani, Eco-Shape Poland Spring, or Vitamin
Water) affect the amount of pressure it can
withstand?
Replies:
Hi Billy,
Interesting question! The shape of the water bottle has little effect
on the pressure it can hold. The most important thing is that the
bottle must be round. Whether it is straight-sided (like a cylinder),
or it gets "skinny" in the middle (like a Coke bottle), for example,
makes no significant difference to its ability to hold pressure.
If the bottle is not round, things get more complicated. Take a square
bottle for example. If you try to pressurize it, the flat sides will
bulge outward, and if there is enough pressure it will actually start
to look round! Water and pop bottles derive almost all their strength
(and ability to resist pressure) by being perfectly round. They can
increase or decrease in diameter at different points along their
length without affecting their strength, provided all sections are
still round.
Regards,
Bob Wilson
The pressure inside a container is the SAME IN ALL DIRECTIONS regardless of
the shape of the container. These bottles are not meant to withstand high
pressure so they should not be pressurized. Failure of the container occurs
at the weakest point of the container. Typically this is a seam (if there is
one), a "thin" spot, or where there is a large curvature such as the base.
Vince Calder
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Update: June 2012
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