# Chapter 17 by wpr1947

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```									Chapter 17

Properties of Gases
Buoyancy and Gases

   Just like liquids, buoyancy is also a property of
gases.
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
displaced.
Charles’ Law
The relationship between temperature and
volume.

Formula: V1/T1 = V2/T2

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

   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
nitrogen.
 Atmospheric Pressure is the force of the air that

is acting on each square inch of the Earth’s
surface.
   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
Boyle’s Law
The relationship between pressure and
volume of a gas under constant
temperature.

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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