PRESSURE AROUND US
Courage is grace under pressure.
-Ernest Hemingway
Here I am going to mention a pressure that is experienced by all living entities and even plays an important role in their life. It is " Air pressure".
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What is air?
Air is a mixture of many gases and tiny dust particles. Air can only exist inside a closed boundary like a bottle, cylinder, atmosphere, etc for life forms to exist. Surprisingly air is a perfect mixture of all the gases i.e air is homogeneous even though it is made out of different gases. So air can be considered a single entity.
How do we interact with air? Without air we can't breathe, plants can't survive, we can't have a stable temperature, we can't fly, and many other interactions that we see, experience, and study it.
What is pressure?
Pressure is the force that is produced when something is pressed by you or something is pressing you. Force is pushing or pulling, in this case, we can consider force as pushing. In science pressure is a physical quantity that is very useful in many concepts like hydrostatic pressure, thermal pressure, fluid pressure, differential pressure, gauge pressure, vacuum pressure, atmospheric pressure, water pressure, etc.
Fluids
Water and gases are called fluids because they exhibit similar behavior that is they can take the shape of a container, are loosely packed, have thermodynamic properties, and can flow. With physical observation, we can say that fluid is a medium in a space that occupies the space and life exist in the fluid or with the help of fluids.
Water and life
As humans, we can't see our faces with our senses but can see others' faces and learn from them in a similar way we don't realize our surroundings. Now let's learn from the life form in water. Take a fish in a pond, a pond has a closed boundary and the fish can move inside it. Now the fish needs oxygen and it gets the oxygen from the resolved oxygen in the water. As we see the fish moves freely in the water without any resistance because the fish lives in that environment. we can see fish living near the surface of the water and fish that go deep as 10000 feet quite interesting right!
Now the water at a depth provides some pressure because some amount of substance is above it. (when a pile of pillows is on your chest we feel pressure in a similar way there is a pile of water above that point). Now lets us do a little calculation to understand what is happing.
Consider a cuboid pond of the following dimensions
10×10×200 (Length×Width×Depth )
Its volume is then given as a 20000-meter cube
Now consider a fish at 10 meters depth. So it has 10 meters high water above it.
So, The volume of water above it is a 10000-meter cube which is 10000000 kg of water or 980 KPa of pressure, Now with a sound mind, we can see the fish should be crushed with that weight but it does not, (We don't usually think this in this way but it is really interesting). A pressure of around 100 KPa is enough to crush a soda can. Here the fish does not get crushed because it doesn't have air inside it and it is mostly fluid so it will balance its body pressure with the water pressure and move around.
Humans, fish, and air
As land-living creatures, we move around the land in a medium filled with air which we don't notice because it is a part of us.
We don’t even realize we are experiencing air pressure until we actually look for it. The things we don’t see at first, and take for granted, like gravity and air pressure, turn out to be among the most fascinating of all phenomena. It’s like the joke about two fish swimming along happily in a river. One fish turns to the other, a skeptical look on its face, and says, “What’s all this new talk about ‘water’?” from the lectures of Walter Lewin.
We live at the bottom of the ocean
From the above discussion, we should come to the idea that we live at the bottom of the ocean which is made up of air, which exerts a huge amount of pressure on us every second of every day. Suppose you hold your hand out in front of you, palm up. Now imagine a very long piece of square tubing that is 1 centimeter wide balanced on my hand and rising all the way to the top of the atmosphere. That’s more than 7000km (More precisely 10000km). The weight of the air alone in the tube (forget about the tubing just think of air or the jube is made up of air). That’s one way to measure air pressure: 1.03 kilograms per square centimeter of pressure which are called the standard atmosphere or 100Kpa. Which is huge. (From Walter Lewin Lectures and demonstrations)
Another way to calculate air pressure is with a fairly simple equation. Pressure is force divided by area: P = F⁄A. So, air pressure at sea level is about 1 kilogram per square centimeter. We know the relation between force, pressure, and area. The larger the area, the lower the pressure, and, conversely, the smaller the area, the larger the pressure.
Now stretch out your hand (palm up) and think about the force exerted on your hand. The area of your hand is about 10 square centimeters, so there must be a 70-kilogram force, about 70 Kg, pushing down on it. Then why you are able to hold it up so easily? Because the pressure exerted by air surrounds us on all sides, and there is also a force of 70 Kg upward on the back of your hand. Thus the net force on your hand is zero. Then why doesn’t your hand get crushed if so much force is pressing in on it? Clearly, the bones in your hand are more than strong enough not to get crushed. (From Walter Lewin Lectures and demonstrations)
How about my chest? It has an area of about 1,000 square centimeters. Thus the net force exerted on it due to air pressure is about 1,000 kilograms: 1 metric ton. The net force on my back would also be about 1 ton. Why don’t my lungs collapse? The reason is that inside my lungs the air pressure is also 1 atmosphere; thus, there is no pressure difference between the air inside my lungs and the outside air pushing down on my chest. That’s why I can breathe easily. Take a cardboard or wooden or metal box of similar dimensions as your chest. Close the box. The air inside the box is the air you breathe—1 atmosphere. The box does not get crushed for the same reason that your lungs will not collapse. Houses do not collapse under atmospheric pressure because the air pressure inside is the same as outside; we call this pressure equilibrium. (From Walter Lewin Lectures and demonstrations)
So it is really fascinating to think about the things around us.
Hope this article was useful and I hope you learned something from it.
If you have any theories or questions regarding this you are free to express them in comments or you can chat with me on my Instagram page https://www.instagram.com/phy.sci/?hl=en.
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