Introductory Lesson about pressure and air or atmospheric pressure in physics Note: some text and questions are lacking.

1. AND
AIR PRESSURE
PREPARED BY
MR. MARVIN GONZAGA AND
MS. AUBREY BARREDO

2. WHAT IS PRESSURE?
Pressure is the force
acting per unit area
In formula:
AREA
FORCE
P = F
A
For a constant force, an
increase in the area of
contact will result in a
decrease in the pressure

3. The standard unit of Force is the Newton (N)
Area is length (in meters, m) times width (also in
meters) and therefore its unit is in m2
Pressure is Force/Area, therefore its unit is N/m2
N/m2 is also known as the Pascal (Pa), which is the
standard unit for pressure
UNITS OF PRESSURE
Other units of pressure include pounds per square
inch (psi), used in US and British standards.

4. INSTRUMENTS FOR MEASURING PRESSURE
Mechanical
Pressure Gauge Manometer
Used for recording pressures
exerted by substances other
than air—water, oil, various
gases
For pressure too small to be
accurately measured by
pressure gauges

5. AIR PRESSURE
or ATMOSPHERIC PRESSURE

6. Atmospheric pressure or air pressure is defined as the force
per unit area exerted against a surface by the weight of the
air above that surface. In the diagram below, the pressure at
point "X" increases as the weight of the air above it increases.
The same can be said about decreasing pressure, where the
pressure at point "X" decreases if the weight of the air above it
also decreases.

7. UNITS OF AIR PRESSURE
In aviation and television
weather reports, pressure is
given in inches of mercury
("Hg), while meteorologists use
millibars (mb), the unit of
pressure found on weather
maps.

8. MEASURING AIR PRESSURE
Thinking in terms of air molecules, if the number of
air molecules above a surface increases, there
are more molecules to exert a force on that
surface and consequently, the pressure
increases. The opposite is also true, where a
reduction in the number of air molecules above a
surface will result in a decrease in pressure.
Atmospheric pressure is measured with an
instrument called a barometer, which is why
atmospheric pressure is also referred to as
barometric pressure.

9. LOW AND HIGH PRESSURE AREAS

10. Sample Problems
1. If a block weighs 60 N and is lying on a side with area
2 m by 3 m, what is the pressure exerted on the
surface?
Solution
Given:
F = 60 N
A = 2 m x 3 m
A = 6 m2
P = F / A
= 60 N / 6 m2
P = 10 N/m2 or 10 Pa
60 N
3 m
P = ?

11. 2. Why does piercing 2 holes in the can allow
milk to flow out faster?
Answer
Piercing another hole opposite to where the milk
comes out allows air to rush in, pushing the milk
out of the can.
If there’s only one hole, the milk trying to get out
will be resisted by the pressure of the air trying to
get in.

12. SEATWORK
1. If 60 Pa of pressure is acting on a box lying on its end
which is 2m x 0.5m, what is its weight in Newtons?
2.

13. THANK YOU!