Ask A Scientist© Physics Archive

name       steve
status     other
age        30s

Question - water will not boil in Colorado or maybe Wyoming because of
high altitudes & potato chip bags burst in shipment due to high pressure
in those areas????im a trk/driver & have been told this for years & i
wonder if there is such a place or issue where this is true?????myth / or fact

Steve -

You are on the right track, but the info lost something in the retelling.

Because of the lower (not higher) atmospheric pressure, water boils at a lower
temperature at higher altitudes. It is therefore more difficult to cook 
food in
boiling water in Denver than in New Orleans. The boiling water will only 
reach...
perhaps 96 degrees C instead of 100. Cooking times are longer. As far as your
potato chip bags... yes, if they are sealed tightly at a lower elevation, the
pressure differential at 6000 feet might cause them to explode. It is the same
reason that when weather balloons are launched they do not appear to be 
full. As
they climb, the gas inside the balloon expands.

Larry Krengel
=========================================================
Steve,

    Water boils when the vapor pressure of water exceeds atmospheric 
 pressure. At
high elevations (such as Colorado or Wyoming) it boils at lower temperatures
because the atmospheric pressure is LOWER at high elevations.  Because the 
boiling
temperature is lower at high elevations foods that are cooked by boiling 
take a
little longer to cook at high elevation.

    Certainly potato chip bags will swell as they are taken to higher 
 elevations
(because the amount of gas in the bag is fixed but the pressure outside is 
reduced,
the gas inside will swell the bag against the reduced atmospheric pressure).
Whether they will burst will depend on how strong the bags are. Usually 
the weakest
point will be the seams of the bags. It is quite likely that at least some 
of the
bags will burst at the seams if they are trucked from low altitude over the
continental divide.
Bradburn
=========================================================
Atmospheric pressure decreases significantly the higher the elevation -- a
lot of other things being equal. So high up in the Rocky Mountains water
boils at a temperature less than 100 C [212 F], but it still boils when the
pressure of the water vapor equals the atmospheric pressure.

I never heard of potato chip bags actually bursting, but if they are
packaged under a positive pressure of some inert gas like nitrogen to
exclude oxygen that could turn the oil rancid, I suppose they could burst
because the pressure of the atmosphere exerted on the bag becomes
sufficiently lower than the inert gas pressure inside the bag so that the
internal pressure exceeds the bursting strength of the bag.

Vince Calder
=========================================================
I used to live at a reasonably high altitude (7200 ft) in New Mexico, and I
can tell you that there IS a grain of truth to what you have heard.

First of all, water WILL boil at high altitudes, but it isn't as hot as
boiling water at sea level. This is because the air pressure is LOWER at
high elevations. Boiling occurs when the water is hot enough to have the
same pressure as the surrounding air, so that it can form bubbles. As water
is heated, its steam pressure rises, until it reaches the pressure of the
surrounding air. At high altitudes, this air pressure is lower than at sea
level, so the water doesn't have to get so hot to get to boiling. Because
the temperature of the boiling water is lower at high elevations than at sea
level, it takes longer to cook things, such as eggs, potatoes, or spaghetti,
at high altitudes than at sea level.

At high altitudes, things like potato chip bags can burst. This is because
they were sealed at low altitude where the air pressure was high, and their
internal pressure is thus the pressure of the air where they were sealed.
At high altitudes, the pressure inside the bag is still the same as sea
level air pressure, but the air pressure outside the bag is lower. This
means that overall the air inside the bag pushes outward harder than the air
outside the bag pushes inward. Sometimes this difference is enough to cause
the bag to fail.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
=========================================================