Pressure

We can feel the pressure every time either from solid, liquid and gaseous object. Example from the solid object is when you were hit by your friend :D how does it feel? is the pressure getting bigger as your friend is getting bigger? It means pressure relates to force. The bigger the force, the bigger the pressure is. Take a piece of paper, try to make a hole by using your finger, can you do it? Try the same way but this time use a nail. Which one faster? It's the nail. So pressure relates to area, the bigger the area, the less the pressure is. Mathematically we can state :
P = F / A
P is the pressure
F is the force
A is the area

The Pascal's law can be applied for the solid pressure. As the hydraulic is put, we can move the bigger force with a small area due to the same pressure on both side.


The liquid pressure is felt when we swim. The deeper we swim, the more pressure we feel, if we do not follow the proper instruction when we dive, we can break our blood vessel. Swimming in the swimming pool is not the same as swimming in the ocean, the differences of the liquid also affect the pressure. The bigger the density of the liquid, the bigger the pressure is. Mathematically it can be stated as :
P = density x gravity x height(depth)
Inside the U tube, the pressure on both tube has the
same value, that is why different density of liquid will have different height.

The gaseous pressure is felt as we surrounded by the air. Instruments to read the air pressure is barometer and manometer. The picture below is a picture of mercury barometer. The reading is shown by the height of the mercury inside the tube.


In a U tube manometer, we can read the scale as the addition or subtraction of the pressure of the gas and the pressure of the liquid, depends on the height of the liquid is above or below the gas pressure. The picture below shows the addition of the gas pressure and liquid pressure.

As we go to the higher land, the less pressure is felt. It can be stated as :
P(in cm Hg) = 76 cm Hg - (height / 100 m)
In the low land, we can said that the air pressure is 76 cm Hg or 1 atm
In the closed room, air pressure will apply the Boyle's Law that is
P1 V1 = P2 V2
P1 is the pressure of room 1
V1 is the volume of room 1
P2 is the pressure of room 2
V2 is the volume of room 2