1. Liquid and Atmospheric
- Pressure -
Liquid and Atmospheric
Pressure
Pressure Measurement
Definition of Pressure
by Rifki Irawan & Fiqri Hakim

2. Pressure F (N) force P (Pa) = Pressure = A (m2) area
Definition of Pressure
Pressure
is the force acting normally
or perpendiculary per unit area
F (N)
force
P (Pa) =
Pressure =
A (m2)
area
SI unit for Pressure is Pascal (Pa) = 1 N m-2

3. “ same force, different area, different pressure “
Weight = 100 N
Area = 0.01 m2
Pressure = 10,000 Pa
Weight = 100 N
Area = 0.1 m2
Pressure = 1000 Pa
“ same force, different area, different pressure “

4. Force = pressure x area = 100 Pa x 6 m2 = 600 N
Example 1.
The wind pressure on the wall is 100 Pa. If the wall has an area of 6 m2, what is the force exert on it?
To solve this problem, you need to rearrange the pressure equation:
Force = pressure x area
= 100 Pa x 6 m2
= 600 N

5. Area = 0.5 m x 1.0 m F = mass x gravitasi Pressure = force/area
Example 2.
A concrete block has a mass of 2,600 kg. If the block measures 0.5 m length by 1.0 m width and 2.0 m height, what is the maximum pressure of the concrete block that can exert when resting on the ground?
(g = 10 m · s-2)
Area = 0.5 m x 1.0 m
= 0.5 m2
F = mass x gravitasi
= 2,600 kg x 10 m · s-2
= 26,000 N
Pressure = force/area
= 26,000 N / 0.5 m2
= 52,000 Pa

6. Liquid and Atmospheric Pressure
“A liquid exerts pressure because of its weight”
Pressure acts in all direction
Pressure increases with depth
Pressure depends on the density of the liquid
Pressure does not depend on the shape of the container

7. Volume liquid = base area x depth = A x h
Weight= mass x gravity
mass liquid = density x volume =  x A x h
“pressure of the liquid depends on the density of the liquid itself”
Weight liquid = mass liquid x gravity =  x A x h x g
mass
Density =
Weight liquid = Force of the liquid =  A h g
volume
Force liquid
 A h g
Pressure liquid =
Area container A
Pressure liquid =  h g

8. Pressure = ρhg = 1,000 kg/m3 x 2 m x 10 N/kg = 20,000 Pa Example 1.
If the density of water is kg/m3, what is the pressure due to the water at the bottom of a swimming pool 2 m deep?
First, define the data which given
Density= kg/m3
Height= 2 m
Gravity= 10 N/kg
Pressure = ρhg
= 1,000 kg/m3 x 2 m x 10 N/kg
= 20,000 Pa

9. Atmospheric pressure
The athmosphere is a deep ocean of air which surround the earth. In some ways, it is like liquid:
Its pressure acts in all directions.
Its pressure becomes less as you rise up through it
Unlike a liquid, air can be compressed.

10. Atmospheric pressure
The pressure that will support a column of mercury mm hight is known as standard atmospheric pressure or 1 atmosphere (1 atm)
1 atm = Pa
In weather forecasting we often used milibar (mb)
1 mb = 100 Pa

11. The instruments The mercury barometer
Atmospheric press the mercury up the tube because the space at the top of the tube has no air in it.
mm Hg = 1 atm