Most of us will feel bored and dizzy when studying physics. This is because there are many 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 sciences that is taught quite often is pressure. Types of pressure, uses of pressure, various pressure calculations, etc. So, what exactly is pressure? What does it do? What types?
To find out pressure, you can listen to the following explanation.
Definition, Formulas and Pressure Units
Pressure is the magnitude of a strong pushing force. In the Integrated Science book for SMP and MTs for Class VIII semester 2 written by Lutfi, et al, pressure is the amount of force acting on each unit surface area. Pressure can occur due to a push on an object in a perpendicular direction.
Pressure is not only related to force, but also to area, temperature and volume. The international unit of pressure is newtons per unit area (N/m 2 ). Meanwhile, the symbol P or p. Apart from that, another unit of measurement for pressure is Pascal (Pa), which is the last name of the physicist, Blaise Pascal.
So it can be said that 1 N/m 2 = 1 Pa
The pressure quantity is a derivative of the basic quantities, length and time. In addition, pressure is a vector quantity, but is expressed in numbers or values. Basically the pressure formula is as below.
P = F/A
Information:
P = pressure in pascals units
F = force in newton units
A = surface area in m2 units
Types of Pressure
Pressure has several types as follows.
1. Pressure of Solids
When a solid substance is given a pushing force from above, pressure will arise. The larger the compressive area, the smaller the pressure. Therefore, the factors that influence the amount of pressure are the pressure force and the area of the field.
The formula for solid pressure is as follows.
P = F/A
Information:
P = pressure in pascals units
F = force in newton units
A = surface area in m2 units
2. Liquid Pressure
Liquid pressure is also called hydrostatic pressure. Hydro means static water or the condition of water that is still. This pressure occurs because the weight of the water 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 x g x h
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 water surface to the depth of the object.
3. Pressure of Gaseous Substances
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 different air pressure. For gas in a closed space, Boyle’s law will apply, namely the pressure and volume of the gas are constant or fixed as long as the gas temperature remains 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 that Influence the Amount of Pressure
Factors that influence the amount of pressure are compressive force and area. The following is a more detailed explanation of these two factors.
1. Compressive Force
Compressive force is a vector quantity that has a value of direction. The compressive force is applied perpendicular to the compressive plane. The amount of pressure is influenced by the compressive force. The greater the pressing force applied, the greater the pressure produced.
For example, when you try to drive a nail into a wall by hand it will never stick. This is caused by the very small compressive force produced by the hand.
Unlike a hammer, when using a hammer, the nails will stick into the wall easily. This is because the hand-driven hammer has a greater pressing force.
2. Compressive Field Area
The influence of the area of pressure can be seen from the pressure formula. Where, the compressive area (A) is the denominator. Meanwhile, the pressing force (F) is the numerator.
This means that the magnitude of the pressing force is perpendicular to the magnitude of the pressure force. So, the area of the compression area is inversely proportional to the amount of pressure. The wider a pressure area, the smaller the pressure generated.
A given compressive force can produce different effects. This depends on the pressure area. The same compressive force will exert greater pressure on a compressive area with a smaller area.
For example, using fingers and syringes. Hand needles have a larger surface area than syringe needles. When both are given the same pressing force, the resulting pressure will be different.
When a pressure force is applied to a person’s hand, the pressure exerted is small. This is due to the large surface area. Meanwhile, when a syringe is applied, a pressing force of the same magnitude is applied to someone’s hand. So, it can penetrate the person’s skin.
This can happen because the pressure area of the syringe needle is smaller than the area of pressure on the finger. All the applied pressing force will be concentrated into a very small area at the sharp tip of the needle.
The same pressing force on an area with a wider distribution on the fingers will produce smaller pressure.