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4.1. The air

The air

Air is not a gas, but a homogeneous mixture made up of several gases that make up the Earth's atmosphere, which surrounds the Earth attracted by the force of gravity. Air is essential for life on our planet.

The atmosphere is the gaseous layer that surrounds the Earth.

Although we will already talk about the composition of the atmosphere, we anticipate that it is made up of 78% nitrogen, 21% oxygen, and the rest are other gases.

The atmosphere is necessary for living beings, since they take from it oxygen for their respiration and carbon dioxide for photosynthesis. In addition, the atmosphere acts as a filter to retain ultraviolet radiation harmful to life and allows a suitable temperature for the development of life to exist.

Aerial view of Chiprana (Zaragoza)

Some characteristics of the air

  • Air weighs. It may seem strange, but it was already demonstrated by Galileo in 1613 that air has mass. We also carry on our shoulders the burden of almost a ton of weight from the air above us. As the air pressure is exerted in all directions, and is also balanced by the internal pressure of the body, it means that we do not end up crushed.

Torricelli, in 1643, proved he calculated atmospheric pressure with the invention of a mercury barometer. His famous experiment consisted of filling a glass tube with mercury, which he turned upside down and left in a container that also contained mercury. Thus, the mercury came out but a large part remained inside the tube. In fact, he verified that, checking it at sea level, there was always 760 mm of mercury left inside the tube.

  • Air is a poor conductor of heat, which makes it a good thermal insulator. This property is used in some windows and buildings, creating an air chamber to prevent heat or cold from entering.
  • Air allows the propagation of sound. Air needs a physical medium (liquid, solid or gaseous) to propagate its waves. Without air, in a vacuum, sound could not be transmitted.
  • Although air is very slightly soluble in water, it is enough for aquatic beings to take it from water.

Interactive activity: The air.

Gaseous state

Matter is made up of particles that occupy space. (We will come back to this when we discuss the states of water in the hydrosphere topic).

Unlike the solid and liquid states, the particles that are part of matter in the gaseous state, air in this case, move in all directions and occupy all available space. Therefore, gaseous matter has a fixed mass, but the volume and shape is variable, since it occupies the entire volume of the container that contains it.