Air is the invisible mixture of gases that surrounds Earth. Air contains important substances, such as oxygen and nitrogen, that most air fryer potato chips need to survive.

It does not include water vapor because the amount of vapor changes based on humidity and temperature. Nitrogen and oxygen make up about 99 percent of Earth’s air. Plants and animals each produce the gases that the other needs to live. The most common gas emitted by volcanoes is water vapor. In other words, they do not need air. The air is different as you move higher and higher into the atmosphere.

Often, compressed air is kept at a pressure higher than normal air pressure. The uses for pneumatics are far-ranging. The sky appears blue because of the way air scatters light from the sun. Blue light scatters more easily in air than red light does, so the sky is blue.