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Gas Pressure

Calculations involving the force per unit area on a surface

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Exploding Marshmallows

Exploding Marshmallows

Credit: abdallahh
Source: http://www.flickr.com/photos/22168167@N00/4680276643/
License: CC BY-NC 3.0

Modern jet aircraft often travel at altitudes of 35,000 feet or so. If no precautions were taken, passengers would soon become unconscious due to lack of oxygen. For comparison, Mount Everest is only 29,000+ feet high and oxygen is needed to climb to the summit.

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Credit: UNC - CFC - USFK
Source: http://www.flickr.com/photos/unc-cfc-usfk/3436442499
License: CC BY-NC 3.0

Oxygen masks are used by pilots traveling at very high elevations [Figure2]

  • Boyle’s Law deals with the relationship between volume and pressure at constant temperature. As the pressure on a gas increases, the volume decreases. If the pressure decreases, the volume will increase. When we squeeze a balloon, we have reduced the volume. The pressure will then increase and may pop the balloon if it increases enough.
  • Ears can “pop” at surprising times. We are all familiar with the ear problems associated with flying, but what about other higher altitude situations? Sometimes your ears can pop (or at least experience a change in pressure) just by driving from a higher altitude down to a lower altitude fairly quickly. There is often enough change in air pressure to create a temporary imbalance between pressures of the outside air and the inner ear.
  • When you get a flu shot (or any other kind) using a syringe and needle, the syringe plunger is pulled back to get the medicine in the syringe. As the plunger is pulled back, the volume of the syringe increases and the pressure drops. These changes allow the medicine to flow from the sterile container into the syringe.
  • Watch a video illustrating Boyle’s Law using marshmallows: https://www.youtube.com/watch?v=ULdmv-iPQvA

Show What You Know

Use the links below to learn more about the relationship between pressure and volume, then answer the following questions:

  1. We can find many online videos in which a marshmallow is exploded by placing it in a microwave oven and turning the oven on. Why is this not an illustration of Boyle’s Law?
  2. When flying at 36,000 feet, what altitude is the cabin pressure set at?
  3. What problems might a person with lung disease have with flying?
  4. Why are high-altitude weather balloons only partially filled when they are launched?

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Image Attributions

  1. [1]^ Credit: abdallahh; Source: http://www.flickr.com/photos/22168167@N00/4680276643/; License: CC BY-NC 3.0
  2. [2]^ Credit: UNC - CFC - USFK; Source: http://www.flickr.com/photos/unc-cfc-usfk/3436442499; License: CC BY-NC 3.0

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