chapter 3 form 4

1. 3.3 GAS PRESSURE
AND ATMOSPHERIC
PRESSURE

2. A. GAS PRESSURE
 Gas pressure – is the force exerted on the walls of
a container by the gas particles per unit area of the
walls.
Gas pressure depends
on
Mass of the gas
- The bigger the mass of
a gas, the higher the
number of gas particles
The velocity of gas
particles
- Velocity influenced by
the gas temperature
Temperature increased,
gas particles move
faster

3. B. ATMOSPHERIC PRESSURE
Characteristics of atmospheric pressure
 Acts equally in all directions
 Not dependent on the surface area of the object
 Influenced by the height of an object above the sea
level. (altitude)
* altitude increase, pressure decrease. It is
because higher it is from the Earth, lower
the density of air.
 Atmospheric at sea level (1 atm)
1 atm = 76 cm Hg = 760 mm Hg
= 10 m H2O
= 1 x 105 Pa
= 1 bar = 1000 milibar (meteorological
purpose)

4. INSTRUMENT MEASURING ATMOSPHERIC
PRESSURE
 Mercury barometer
- also known as simple barometer
- the height of mercury column in the long
tube varies with the magnitude of atmospheric
pressure
- disadvantage = difficult to be carried
around, mecury can spill and glass tube can
be broken

6.  Fortin barometer
- improved version of a simple barometer
- consists of
a) vernier scale – give more accurate
reading
b) mirror behind the scale – avoid
parallax error
- measured in the unit mm Hg
 Aneroid barometer
- alternative instrument to measure
atmospheric pressure

8. INSTRUMENT MEASURING GAS PRESSURE
 Manometer
- u-tube filled wth a liquid such as mercury
 Bourdon gauge
- instrument used to measure
the pressure of gas
- commonly used in schools
hospitals and factories.