AND

AIR PRESSURE

PREPARED BY

MR. MARVIN GONZAGA AND

MS. AUBREY BARREDO

WHAT IS PRESSURE?

Pressure is the force

acting per unit area

In formula:

AREA

FORCE

P = F

AFor a constant force, an

increase in the area of

contact will result in a

decrease in the pressure

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.

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

AIR PRESSUREor ATMOSPHERIC PRESSURE

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.

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.

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 pressureincreases. 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.

LOW AND HIGH PRESSURE AREAS

Sample Problems

1. If a block weighs 60 N and is lying on a side with area2 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 = ?

2. Why does piercing 2 holes in the can allow

milk to flow out faster?

Answer

Piercing another hole opposite to where the milkcomes 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.

SEATWORK

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

2.

THANK YOU!