When we think of the sky and the miles and miles of air above us, words like freedom and weightlessness often come to mind. And while soaring through all that space is undoubtedly freeing, science says otherwise about its perceived lack of weight. The air around us, specifically our planet’s atmosphere, is composed of numerous microscopic molecules that, although pretty light individually, become quite weighty in great numbers. This begs the question: If these molecules are weighing down on us at every moment of our day, why does it not feel like it?
How Equilibrium Plays a Role
The air particles exert a certain amount of pressure on the entire human body, but what is fascinating is that the air molecules within the body also exert the same amount of pressure in return, resulting in a state of equilibrium.
This effect stems from humanity’s evolutionary journey over the years in the presence of air, enabling it to adapt to the constant pressure it receives at all times. If the human body did not contain the assortment of bones, organs, muscles, and other such things that keep it alive, it would immediately pop like a tin can upon exposure to atmospheric pressure.
One can, therefore, conclude that there is a phenomenon of pressure equalisation involved, hence the lack of any pressure difference and why we don’t feel the crushing weight of the air. However, let us imagine for a moment that this was not the case.
To do so, draw a one-inch by one-inch square on your palm. The 100km of air directly above that square has a total mass of approximately 7 kg and, under the influence of gravity, would push down on the square inch of your skin with a force of around 15 lbs, the same weight as an average bowling ball.
Apart from the lack of any difference in pressure between our innards and the outside air, there is another reason why we don’t feel anything as far as atmospheric pressure is concerned.
Air Is a Fluid
You may recall your physics tutor in Singapore touching on how air behaves like a fluid. It can take any form and flow in all directions and transmit the crushing force of its weight while doing so (even upwards). Going back to the previous example with our palm, it would feel the air pushing down on it with the force of a bowling ball. Simultaneously, the air pushes it back up with the same force, cancelling the two pressures.
In other words, both the top and bottom surfaces of your hand feel the air pressure, but as a whole, your entire hand feels no net force from the atmosphere. This fluid nature of air, which causes the weight of the atmosphere to push everywhere in on us but never down, is why we do not feel the crushing weight of the hundreds of kilometres of air above.
That said, this cancelling of forces only takes place if atmospheric air can reach both the palm and back of your hand. Should the air exerting force on either side of your hand be removed, this cancellation phenomenon ceases to exist. In fact, this can be partially achieved with the help of a powerful vacuum machine.
Simply place the hose’s opening directly against the back of your hand, and the air acting upwards on it is temporarily removed, allowing you to feel the air pressure and its downward force on your palm. While it may seem like this force is caused by the hose sucking on your hand downwards, it is, in fact, coming from the weight of the air above.
Conclusion
Learning about mysterious ways nature balances all variables in its ambit such that all the natural conditions sustain and progress life on Earth is always an eye opener. At Tuition Physics, we provide engaging classes and booster programs that not only help you achieve your academic goals and beyond but also explore the everyday aspects of physics within our known universe. If you are interested in pursuing either of these two, don’t hesitate to contact us today to learn more about our syllabi and class schedules for our IP and O-level physics tuition in Singapore!
