Physics teaches us about many things and makes life easier. Making the tools we use in everyday life refers to the laws of physics. For example, nail clippers apply simple plane theory.
Most of us will feel bored and dizzy when studying physics. This is due to the large number of formulas and the complexity of how to calculate the numbers. However, basically physics will be easy to learn by understanding the basic concepts.
One of the physics that is often taught is pressure. Various pressures, uses of pressure, various pressure calculations, and others. So, what exactly is pressure? What does it do? What types?
To find out the pressure, You can listen to the following explanation.
Definition, Formulas, and Pressure Units
Pressure is the magnitude of the strong pushing force. In the SMP and MTs Integrated Science book for Class VIII semester 2 written by Lutfi, et al, pressure is the magnitude of the force acting on each unit surface area. Pressure can occur because of a push on an object in a perpendicular direction.
Pressure is related not only to force, but also to area, temperature, and volume. The international unit of pressure is the newton per unit area (N/m 2 ). While the symbol P or p. In addition, another unit of measurement for pressure is Pascal (Pa) which is the last name of the physicist, Blaise Pascal.
Then it can be stated that 1 N/m 2 = 1 Pa
The magnitude of pressure is a derivative of the principal quantities, length, and time. In addition, pressure is a vector quantity, but is expressed in numbers or values. Basically the pressure formula as below.
P = F/A
Information:
P = pressure in Pascals
F = force in newtons
A = surface area in m 2 units
Types of Pressure
Pressure has several types as follows.
1. Pressure Solids
In solids that are given a thrust from above, pressure will arise. The greater the area of the press field, the smaller the pressure. Therefore, the factors that affect the amount of pressure are the pressure force and the area of the field.
The formula for the pressure of a solid is as follows.
P = F/A
Information:
P = pressure in Pascals
F = force in newtons
A = surface area in m 2 units
2. Liquid Pressure
Liquid pressure is also known as hydrostatic pressure. Hydro means static water in still water conditions. This pressure occurs because of the weight of the water which makes the liquid exert pressure. The pressure of a liquid depends on the depth of the liquid in a chamber and gravity also determines the pressure of the water.
The formula for liquid pressure is as follows.
P = p xgxh
P = hydrostatic pressure (Pascal or N/m 2 )
p = density of liquid (kg/m 2 )
g = acceleration due to gravity (10 m/s 2 )
h = depth of liquid (meters), calculated from the surface of the water to the depth of the object.
3. Gas Substance Pressure
Earth has a protective layer in the form of an atmosphere. This layer extends up to 1000 km above the earth and has a mass of 4.5 x 1018 kg. The mass of the atmosphere pressing on the surface is called atmospheric pressure. Atmospheric pressure at sea level is 76 cmHg.
Every place has a different air pressure. Gas in a closed space will apply Boyle’s law, namely the pressure and volume of gas are constant or fixed as long as the temperature of the gas is still the same.
The gas formula in a closed room is as follows.
px V = constant
p1 x v1 = p2 x v2
The mixed gas formula is as follows.
(p1 x v1) – (p2 x v2) / (v1 + v2)
Information:
p1 = initial atmospheric pressure (atm)
v1 = initial volume (m 3 )
p2 = final atmospheric pressure (atm)
v2 = final volume (m 3 )
Factors Affecting the Amount of Pressure
The factors that affect the amount of pressure are the compressive force and the area. The following is a more detailed explanation of these two factors.
1. Press Force
The compressive force is a vector quantity that has a direct value. The compressive force is applied perpendicular to the compression plane. The amount of pressure is influenced by the compressive force. The greater the compressive force given, the greater the pressure generated.
For example, when trying to drive a nail into the wall by hand it will never stick. This is caused by the compressive force generated by the hand is very small.
Unlike the hammer, when using a hammer, nails will be stuck in the wall easily. This is caused by the hand-driven hammer having a greater compressive force.
2. Area of Press
The influence of the compressive field area can be seen from the pressure formula. Of which, the compression area (A) is the denominator. Meanwhile, the compressive force (F) is the quantifier.
This means that the compressive force is perpendicular to the pressure force. Thus, the area of the compressive field is inversely proportional to the amount of pressure. The wider a field of pressure, the smaller the pressure generated.
A given compressive force can produce different effects. It depends on the pressure field. The same compressive force will provide greater pressure on the compressed area with a smaller area.
For example in the use of fingers and syringes. Hand needles have a larger surface area than syringe needles. When both are given the same compressive force, the resulting pressure will be different.
When the finger of the hand is given a compressive force to suppress someone’s hand, the pressure exerted is small. This is due to the large surface area. Meanwhile, when the syringe is given a compressive force of the same magnitude to suppress someone’s hand. So, it can penetrate the person’s skin.
This can happen because the area of the syringe press is smaller than the area of the press of the fingers. All of the applied force is concentrated into a very small area on the sharp end of the needle.
The same compressive force on the area with a wider distribution on the fingers will produce a smaller pressure.
The Benefits of Pressure in Everyday Life
Pressure is very useful for everyday life. Here are some tools or objects that use pressure as their working principle.
- Hydraulic pump to help wash the car.
- The soles of the shoes are made flat to apply minimal pressure to the floor so they don’t poke into the floor.
- Small dots under the football boots to put a lot of pressure on the ground. So, ball players can tread firmly on the ground and not slip easily.
- The tips of the nails are made sharp to apply great pressure and easily stick into boards, wood or walls.
- The ax is made sharp to increase the pressure making it easier for carpenters to cut or split wood.
- The blade is made thin to apply great pressure to the object so that it is easy to cut.
- The base of the table is made flat to provide little pressure on the floor. So, don’t stab the floor.
- The tip of the needle is made sharp so that it exerts great pressure and makes it easier to puncture.
Example of a Pressure Problem
The following are examples of questions that can be used as learning references by You in learning pressure.
1. Determine the hydrostatic pressure of water at a depth of 5 meters (ρ = 1,000 kg / m 3 ) and the acceleration due to gravity is 10 m / s 2 .
Answer:
Is known:
h = 5 meters
ρ = 1000 kg / m 3
g = 10 m / s 2
Asked:
p h ……..?
Completion:
p h = ρ . g. h
= 1,000 . 10 . 5
= 50,000 N / m 2 or Pa, or
= 50 kPa (kPa = kilopascal)
2. The pressure of the liquid is 3,000 Pa, the height of the liquid is 30 cm, what is the density of the liquid?
Answer:
Is known:
p = 3,000 Pa
h = 30 cm = 0.3 m
Asked:
ρ….?
Completion:
p h = ρ . g. h
3.000 = ρ . 10 . 0.3
ρ = 3,000 / 3
ρ = 1,000 kg / m 3
So, the density of the liquid is 1000 kg / m 3 .
Answer:
Is known:
h = 2 m
ρ = 1000 kg / m 3
g = 10 m / s 2
Asked:
p h …….?
Completion:
p h = ρ . g. h
= 1,000 . 10 . 2
= 20,000 Pa, or
= 20 kPa
So, the hydrostatic pressure at that depth is 20 kPa
4. The height of a city is 300 meters above sea level (above sea level). What is the air pressure in that city?
Answer:
Is known:
Altitude = 300 m
Asked:
Air pressure…?
Completion:
Air Pressure = 76 cmHg – ( Altitude / 100 meters )
= 76 cmHg – ( 300 meters / 100 meters )
= 76 cmHg – 3
= 73 cmHg, or
= 730 mmHg
5. A cylinder with a volume of 2 m 3 has a pressure of 6 atm, then the volume is reduced to 0.5 m 3 . What’s the pressure now?
Answer:
Is known:
V 1 = 2 m 3
p 1 = 6 atm
V 2 = 0.5 m 3
Asked:
p2 …… ?
Completion:
p.1 . _ V 1 = p 2 . V 2
6 . 2 = p 2 . 0.5
p 2 = 12 / 0.5
p 2 = 24 atm
So, the pressure now is 24 atm.