<center>https://cdn.pixabay.com/photo/2015/03/26/09/42/mountain-690122_960_720.jpg</center> <center>[Image source: Pixabay](https://pixabay.com/en/mountain-summit-peak-top-altitude-690122/)</center>

Let's consider our friend Sue, and her bicycle on a sunny day. She was about going out to see her friend and she just discovered the rear tyre was flat. So what should she do to revive her bicycle? well, for starts, it obviously needs lots of air to revive, and to do that, Sue's gonna need a bicycle air pump. By simply attaching the air pump to the stem on the bicycle wheel, she forms a passageway for fluids to flow from the pump to the tyre. In a few minutes, Sue's bicycle is ready to roll!

 We live in a world of pressure, and in getting things done, some sort of force must be applied, and energy transferred. We need pressure for cooking, for making cars more safe by installing brakes *(which operates on the principle of pressure)*, for propelling man into space through fuels and so on!. Getting to know how pressure in fluids work is to a great advantage to us as science enthusiast, and today, I am gonna write about fluid pressure, and more specifically; fluid pressure in our atmosphere. -the sky-.

<div class="pull-right"><center><img src="https://c.pxhere.com/photos/f2/24/bike_cycling-225213.jpg!d" /><br/><em><a href="https://pxhere.com/en/photo/225213">Image source: Pixhere</a></em></center></div

If you really had a bicycle, and maybe you've pumped air into a bicycle tyre before, then you'd reckon that air is observed to flow into the tyre as you operate the air pump. In a short time, it expanded and became firmer. and by squeezing the bicycle tyre, we could judge and tell if the pressure is just right.

The science behind the strength of the bicycle tyre isn't hard to grasp at all. It is as a result of pressure. You see, as we pump air into the tyre using the air pump, this air contain millions and millions of air particles that are constantly moving at very high speeds and colliding with each other, as well as the walls of the tyre. The force/pressure exerted by these particles of air forces and expands the tyre outwardly so that it stretches and becomes harder as air is continually being pumped in. Basically, by confining so much air into an enclosed small area, we create pressure and the constant quest for these molecules to cover more space make them keep the tyre pumped!

<center>https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Pressure_force_area.svg/600px-Pressure_force_area.svg.png</center> <center><sub>
***Pressure illustration. Klaus-Dieter*** [<a href="https://creativecommons.org/licenses/by-sa/3.0">CC BY-SA 3.0</a>], <a href="https://commons.wikimedia.org/wiki/File%3APressure_force_area.svg">Wikimedia Commons</a></sub></center>

#
The force these air molecules exert in a small given area of the tyre is known as pressure. And for my math-loving readers, here's a definition from wikipedia that perfectly suits your taste:

Pressure is defined as the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

Mathematically;

## <center> Pressure (P) = Force (F) /Area (A) </center>
#
And it's S.I unit is the pascal (Pa), named after Frenchman Blaise Pascal, who worked on atmospheric pressure in the late 1640s.

Other units for pressure include the N/m<sup>2</sup>, the bar, the torr, the pounds/square inch (psi), etc.

Now, let's consider the fluid pressure in our environment and surrounding, particularly in the atmosphere.



<div class="pull-left"><center><img src="https://images.pexels.com/photos/62623/wing-plane-flying-airplane-62623.jpeg?w=940&h=650&auto=compress&cs=tinysrgb" /><br/><em><a href="https://www.pexels.com/photo/gray-plane-wing-62623/">Image source: Pexels</a></em></center></div

If we remember anything about fluids, then it is their awesome ability to assume a free form and flow unlike solids that are fixed and static. Fluids easily take the shape of their container, filling all the spaces from the bottom up.

Ever boarded an aeroplane for transportation? or occasionally gone skinny dipping into the river? then you probably could asseverate that at some point you have felt your ears pop in the heights, or felt a sharp pain in your ears when descending the watery depths.  Or how about that time your empty plastic water can got squeezed on its own when you and the gang went mountain climbing atop mount Everest? Well, these experiences and more, occur as a result of the pressure difference and its effects on the surrounding fluids, which are air and water in this case.

Hence, we know that pressure changes with respect to the altitude or height.
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# Pressure and the Atmosphere --- Thick or thin!
#
Let's consider the atmosphere as a huge mass of fluid, made up of tiny air particles, around us, and spanning several kilometres above us. Hence we could say we live at the bottom of this fluid.

Since we're living at the bottom of an ocean of air, we experience pressure caused by the weight of the air being pulled to the centre of the Earth by gravity, and this pressure at surface level stands at a staggering average magnitude of about 100,000 Pa!
<center>https://upload.wikimedia.org/wikipedia/commons/8/88/Atmospheric_Pressure_vs._Altitude.png</center> <center>[***Image source: Wikimedia***](https://commons.wikimedia.org/wiki/File:Atmospheric_Pressure_vs._Altitude.png)</center>

However, at various layers and altitudes in the atmosphere, air pressure varies from each other, gradually reduces and air thins out as you ascend into the vacuum space *(where there is no air particle and weightlessness occurs).* This is particularly why mountain climbers take with them oxygen tanks to aid breathing at such a high altitude. The chart above illustrates the correlation between atmospheric pressure and altitude.

We might have been exposed to the formula for calculating pressure in fluids at a given height from the ground as;

# <center>P = p x g x h</center>

Where:
**P= Pressure;**
**p= Density of fluid;**
**g= Acceleration due to gravity;**
**h= Height from main sea level**

And we realize that the density of air at the surface is heavier due to gravity, and begins to lighten up as we ascend with about 1 millibar drop in pressure for every 8 meter climb!

So, let's consider various air pressures at respective altitudes from the earth's surface. 

#### Edge of space!
The edge of space is at the topmost layer of the atmosphere at a height of about 150 km -The Exosphere-. This altitude contains very little air particles *(As there exists about one hydrogen molecule in a cubic centimeter of )* and the pressure is very close to zero. Beyond this region is considered "Space". 

#### At the stratosphere.
At the stratosphere where the ozone layer exists *(which lies between 20 - 50 km from the earth's surface)*, the air pressure is at a magnitude of about 100 Pa.

Just below that height to where jet streams aid aircraft flight, the pressure present is about 25,000 Pa. The air quality is very thin from what humans are used to. Hence, airplane are fitted with pressurized cabins to enable passengers breathe comfortably.

#### On mountains.

On the top of very high mountains, say about 6 to 10 km from sea level, air pressure is about 50,000 Pa, which is just about half of what we have at sea level where most living things reside!


#### Sea level.
At sea level where we live, a column of air that is as high as 150 km presses down on the earth's surface. Hence, pressure here is at a staggering magnitude of 101,300 Pa. To give an idea how large those numbers are, consider something as heavy as a school bus sitting on everyone... you get the idea!

#### Hold on a second! If it's the pressure on us is that huge, why aren't we getting crushed?
#
> ***I'd say we have Equilibrium and human evolution to thank for that!***
#
https://c.pxhere.com/photos/7f/eb/astronaut_spacesuit_under_water_weightlessness_training_water_pool_helmet-836641.jpg!


<div class="pull-right"><center><img src="https://c.pxhere.com/photos/7f/eb/astronaut_spacesuit_under_water_weightlessness_training_water_pool_helmet-836641.jpg!d" /><br/><em><a href="https://pxhere.com/en/photo/836641/">Image source: Pxhere.com</a></em></center></div

Humans have been here long enough to adapt to such atmospheric conditions. Also, atmospheric pressure *(like every other force known to the physical world)*, balances out in a sorta way. How that happens is that the air molecules inside our lungs and ears exerts an equal magnitude of pressure on our insides that counters the effect of the atmospheric pressure constantly trying to crush us from all sides.  Also, liquids in our bodies, which are incompressible, pushes beck with the same pressure too. Hence, the net force or pressure on our body is zero. thus,we remain in one piece and do not feel a thing.

<center>![](https://static.wixstatic.com/media/203872_bb29e956be4b47bab6212ab9379b8cfe~mv2.gif)</center>

So, I'll like to wrap this up with some cool questions as regards the effects of pressure on humans at various altitudes. lets tag the questions as a and b.

I'd mentioned that your ears would pop and hurt when you're high up the atmosphere and deep down underwater respectively.

a. What becomes of a space enthusiast who manages to get to space without a space suit?

b. Also, what becomes of a diver who decides to brave the trenches without the proper equipment?

## N/B: Give it a thought for a minute would ya... And then proceed to see the answers below!
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**Here are the answers!**

**a.** Our space enthusiast friend would stretch out like a balloon *(supposing he even makes it there alive)*, due to the elasticity of the human skin. Then given the fact that our internal pressure is as high as 14.7 pounds/square inch, in space where pressure is non-existent, He literally would burst open and then all the liquid on the inside of him would instantly freeze. YUCK!

**b.** As for our unprofessional diver dude, you guessed right. He would implode and compress because the external pressure deep in the ocean is over six times greater than the pressure within the human skin. How about that for a morning thought! eh?


Thank you for reading
Stay outta trouble.
@pangoli
***
### References:
***[1](http://www.physics.org/facts/air-really.asp), [2](https://www.ck12.org/earth-science/pressure-and-density/lesson/Pressure-and-Density-of-the-Atmosphere-MS-ES/), [3](http://scienceline.ucsb.edu/getkey.php?key=1711)***

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