Like every Friday, the "A Taste of Physics" corner is back — number 7.
This week: atmospheric pressure, boiling point, and their connection to geyser eruptions.
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Although air seems weightless, it is actually remarkably heavy — 10 tons per square meter, to be precise, or 1 kilogram per square centimeter.
We don't feel this weight because air surrounds us from every direction.
The weight of air is known as atmospheric pressure, and it bears down on everything at Earth's surface, including the water we boil in a pot.
During boiling, the heat added to water molecules causes them to move faster and collide with one another, which separates the molecules and converts them from a liquid into steam — a gas.
Atmospheric pressure presses down on the water's surface and prevents the energetic molecules from escaping into the air as vapor, until the water reaches its boiling point — around 100 degrees at sea level, at which point the molecules are moving fast enough to overcome atmospheric pressure and escape into the surrounding air.
In a pressure cooker, artificial pressure is created by a lid that prevents the water from evaporating, allowing its temperature to exceed 100 degrees so that food cooks faster.
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So what happens in a geyser?
A geyser forms when water accumulates in narrow underground channels above a hot magma source at the bottom.
The water at the bottom of the geyser boils, but cannot turn to steam because the water above it is pressing down on it.
The temperature of the water at the bottom keeps rising, and at a certain point steam bubbles find their way out through the channels in the ground.
The release of these bubbles creates a void at the bottom of the geyser, which allows the superheated water to flash instantly into steam, burst outward at high speed — and the cycle repeats.
The eruption ends when fresh, cold water flows into the geyser and the process begins again.
In the video: a particularly violent eruption of a geyser in Yellowstone National Park.
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