Pressure & Its Applications | Physics for JAMB PDF Download

Force, Pressure and Its Applications

Pressure is the force per unit area. The SI Unit of Pressure is the pascal (Pa). A pascal can be defined as a force of one newton applied over a surface area of one meter square. In other forms,
Pressure = Force  / Area
The pressure is dependent on the area over which the force is acting, without any change in the force, the pressure can be increased and decreased. The Force applied to be constant if the surface becomes smaller the pressure increases and vice versa.

Some Practical Examples

Let us take an example of pressure: take into consideration a sharp needle, it has a small surface area. However, consider a pencil which is very blunt in the back. It has more surface area than the needle. If we poke the needle in our palm, it will definitely hurt us as the needle gets pierced inside our skin whereas if we poke the blunt side of the pencil into our hand it wouldn’t pain at all.
It is due to the fact that the area of contact between the palm and the needle is very small, further the pressure is in a way large. However, the area of contact between the pencil and the palm is more, therefore the pressure is less.
Another example we can take as – A brick sitting on a surface exerts a force equal to its weight on the object it is resting on. Now we know that a rectangular brick has a wide surface and thin surfaces on the sides. By changing the orientation of the brick resting on a surface, we are effectively changing the pressure acting on the surface by the same brick. You can refer to the image below for other information –

By this we can conclude that the two factors that determine the magnitude of the pressure are:

• Force: The force which states that the greater the force, the greater is the pressure and vice-versa.
• Coverage Area: which states that the greater the area less is the pressure and vice-versa.

Daily Life Pressure and Its Application

The application of atmospheric pressure, or in simple words, air pressure is referred to as the numerous activities that we do or observe every day without a realization of any kind of push or pressure. We are able to survive this high-pressure condition as we have evolved and somewhere managed our body functions withstand this amount of high pressure.

Solved Example for You on Pressure and Its Application

Question. What is the excess pressure inside a bubble of soap solution of radius 5.00 mm, given that the surface tension of soap solution at the temperature (20 °C) is 2.50 × 10^–2 N m^–1? If an air bubble of the same dimension were formed at depth of 40.0 cm inside a container containing the soap solution (of relative density 1.20), what would be the pressure inside the bubble? (1 atmospheric pressure is 1.01 × 10⁵ Pa). 
Solution: Excess pressure inside the soap bubble is 20 Pa; 
Soap bubble is of radius, r = 5.00 mm = 5 × 10^–3 m
The surface tension of the soap solution, S = 2.50 × 10^–2 Nm^–1
A relative density of the soap solution = 1.20
Density of the soap solution, ρ = 1.2 × 10³ kg/m³
Air bubble formed at a depth, h = 40 cm = 0.4 m
Radius of the air bubble, r = 5 mm = 5 × 10^–3 m
1 atmospheric pressure = 1.01 × 10⁵ Pa
Acceleration due to gravity, g = 9.8 m/s² 

Hence, the excess pressure inside the soap bubble is:
P = 4S/r
= (4×2.5×10^-2)/5×10^-3 
= 20Pa

Therefore, the excess pressure inside the soap bubble is 20 Pa. The excess pressure inside the air bubble is :
P’=2S/r
=(2×2.5×10^-2)/5×10^-3
=10Pa 

Therefore, the excess pressure inside the air bubble is 10 Pa. At a depth of 0.4 m, the total pressure inside the air bubble,
Atmospheric pressure + hρg + P’
=1.01×10⁵+0.4×1.2×10³x9.8+10 
=1.057×10⁵Pa 
=1.06×10⁵Pa 
Therefore, the pressure inside the air bubble is 1.06×10⁵ Pa. 
This concludes our discussion on the topic of pressure and its application.