Properties of Air: Air Pressure

Take one plastic bag, a jar, and a rubber band. Pull the plastic bag onto the jar and close it with the rubber band so that the bag hangs loosely on the jar. Try to push the bag into the jar. Did you succeed?

Now remove the rubber band, push the bag into the jar and fold the edges of the bag onto the jar neck. Place the rubber band on the edges again. Try to pull the bag out of the jar. It's not that easy, is it?

When you try it, you can feel how some force prevents you from pushing the plastic bag into the jar, and in the second experiment, from pulling it out. This force is caused by air pressure, more precisely by its change in the jar. In the first attempt, you compress the air in the jar and create more pressure there than is outside the jar. To push the plastic bag deeper into the jar, you need to apply extra force. When the bag is pulled out, the air in the jar expands, and the pressure becomes lower than in the outside air, so you have to use force again.

The experiment is similar to the one from the previous lesson, except that we then heated and cooled the air in the bottle. In the heated bottle, the air particles began to move faster and hit the wall of the balloon more often. As a result, the pressure in the balloon also increased.

We are at the bottom of the air layer that surrounds Earth. The air column above our head, with a surface area of 1 cm², contains about one kilogram of particles. The air in the palm of an adult with an area of 100 cm² is thus pressed with force equal to the weight of a hundred kilos! Fortunately, the air pressure affects both sides of the hand in the same way, and that is why we don't feel the weight of the air. But how does our body endure such pressure? This is where the pressure inside our bodies comes to the rescue. It presses just as hard from the inside against the external air pressure.

The near-earth air layer is the most compressed under the weight of the air layers above it. The air is the densest here, and the pressure is the highest. As we move away from the ground, the thickness of the air layer above us decreases. Thus, the air pressure drops when we move higher, and the air becomes thinner.

Humans and animals are used to the air pressure near the ground and do not usually pay attention to it. However, we immediately notice a sudden decrease or increase in air pressure. Anyone who has flown a plane has definitely felt uncomfortable in their ears during both take-off and landing. The point is that the pressure of the air in our ears does not change as quickly, and as the plane takes off, the eardrum films are pulled outwards, and when the plane descends, they are pushed inwards. A sudden change in weather is also linked to a rapid change in air pressure. For example, many people can predict the weather based on how they feel, especially if they are older.

Hikers get tired faster in the higher mountains. They feel short of breath precisely due to the decrease in air pressure, and the resulting thinning of the air. There is no air, or air pressure, in outer space, and the astronauts can only get out of the spacecraft in a special spacesuit made of durable materials. Air is pumped into the spacesuit to create the air pressure to which the person is used to.