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Why No Explosion?

  1. May 23, 2005 #1
    It is scientific fact that that if all else is held constant, the pressure of a gas varies directly with its temperature. In other words, if you have a gas in a sealed, insulated, rigid container and you double its temperature, its pressure will also double. If you triple the temperature, the pressure will triple, etc. This is not EXACTLY true, but it is close enough for the purpose of this teaser.

    Why is it, then, that If I were to fill my tires with 32 psi of air on a day that is 2 degrees Celsius, the tires won't explode if the temperature later increases to 20 degrees Celsius (which would seemingly increase the pressure 10-fold to 320 psi, well beyond the capacity of most tires)?

    Assume that the temperature of the air in the tire always matches the temperature outdoors: it starts at 2 degrees and ends at 20 degrees.
    Also ignore the fact that the tires will expand.
  2. jcsd
  3. May 23, 2005 #2
    Something to do with the temperature scale, you need to find Kelvin for the answer.
  4. May 24, 2005 #3
    Someone slashed your tire!
  5. May 24, 2005 #4
    The pressure will only increase by about 1.07-fold instead of 10-fold.
  6. May 24, 2005 #5
    The theoretical max. air temperature after compression is that calculated by adiabatic process and is much above 2deg.C. Considering heat loss to ambient and polytropic process, actual temperature reduces but still above 2deg.C. Further, filled air temperature need not be equal to that of ambient air due to the resistance of tube and tyre material.
  7. May 24, 2005 #6
    can some one explain that ?
  8. May 24, 2005 #7
    Although I'm sure this makes sense to people who know more about this than me, I think the basic reason is explained by AntonVrba and wave.

    Gas equation takes into account temperature in Kelvin's scale pV = nRT, so tenfold increase wouldn't be 2°C -> 20°C but 275 K (= 2°C) to 2750 K = (2477 °C). But I think you'd have to worry about your tires melting then, not bursting :)
  9. May 24, 2005 #8


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    Anton and wave have both hinted at the answer.

    The OP was wrong to use the Celsius scale. He should have used Kelvin. Doubling 2 degrees Celsius gives 277 Celsius, not 4 degrees Celsius.

    In any case, he's either left or been banned, so there's no helping some people...
  10. May 24, 2005 #9


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    I got a PM from the OP inviting me to join another forum. Thought it was kind of strange. Suspect the OP spam'd all of us good folks here on PF.
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