Chapter 17 by wpr1947


									Chapter 17

Properties of Gases
            Buoyancy and Gases

   Just like liquids, buoyancy is also a property of
               How do balloons float?

    Answer: They displace a very large volume of air.
    This volume of air weighs more than the total
    weight of the balloon. Hot-air balloons float
    because they weigh less than the volume of air
               Charles’ Law
    The relationship between temperature and

            Formula: V1/T1 = V2/T2

   The volume of gas increases as temperature
   The volume of a gas decreases with
    decreasing temperature.
             Gases and pressure
   Pressure is the force acting on a unit area of

   Pressure is usually measured in units of pound per
    square inch (psi).
      Example: Bicycle tires

   SI unit for pressure is called pascal (Pa)
      One pascal = one newton of force acting on one
       square meter of surface area.
             Atmospheric pressure

   The air we breathe is made up of many different
    gases including carbon dioxide, oxygen, and
      Atmospheric Pressure is the force of the air that

       is acting on each square inch of the Earth’s
          This pressure is created by the force of the Earth’s
           gravity pulling the air towards the surface.
                   Air Pressure
   Why do my ears pop?
    If you've ever been at a higher altitude, you may have
    noticed that your ears pop and you need to breathe
    more often. As the number of molecules of air
    around you decreases, the air pressure decreases.
    Your ears will “pop” to balance the pressure. If you
    were on top of Mt. Everest you would be breathing
    fewer molecules of oxygen. You would need to
    breathe faster to help your body get more oxygen.
                Boyle’s Law
    The relationship between pressure and
        volume of a gas under constant

          Formula: P(1)V(1) = P(2)V(2)
                   (Initial)   (Final)

    Boyle’s Law states that you increase the
    pressure as the volume decreases, and
    you decrease the pressure as you increase
    the volume.
         Boyle’s Law in action
   You have a beach ball and a basketball. Obviously the
    beach ball is bigger than the basketball.
   Pump enough air into the beach ball to inflate it fully.
   Pump the same volume of air into the smaller
      The basketball will have much more pressure in it
       due to the fact that there are many more air
       molecules colliding with the smaller surface of the
      Thus increasing the pressure as volume decreases!

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