And once again Friday is here, along with the weekly column "A Taste of Physics" — issue #33.
This time: what makes liquid nitrogen so fascinating, and what happens when you pour it on ping-pong balls.
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In the video you can see what happens when ping-pong balls come into contact with liquid nitrogen.
The balls fly out of the containers as if blasted by an explosion.
Why does this happen?
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Nitrogen is the most abundant gas on Earth — making up about 78% of the atmosphere.
It is also one of the most useful gases.
In industry it is used for rapid deep-freezing of food, in agricultural fertilizers, for filling light bulbs, in the manufacturing of electronic components, for preventing the oxidation of wine, and many other applications.
It can also be found in bitter beverages such as coffee, because when it contacts the palate it creates a sensation of false sweetness.
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Nitrogen becomes a liquid only at a very low temperature: minus 196 degrees.
In a gas, the molecules collide with one another at high speed.
As the gas cools, this motion gradually slows until it is slow enough to allow bonds to form between the molecules, producing a liquid.
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Liquid nitrogen is produced from air.
First, the air is compressed into a membrane chamber (a container whose walls act as a filter), where all the other gases mixed into the air are pushed out, leaving behind pure nitrogen.
In the next stage, the nitrogen is cooled using a helium piston, similar to an air-conditioning system.
The helium is compressed, and as it expands again it draws heat away from the nitrogen, cooling it down.
The process is very slow: after 4 hours of cooling 5 liters of nitrogen, only 50 milliliters of liquid nitrogen are obtained.
When the nitrogen is poured onto the ping-pong balls, it heats up rapidly and turns back into a gas.
This expansion increases its volume by a factor of 700, creating a blast wave that sends the balls flying in every direction.
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Liquid nitrogen also has many industrial uses as an especially efficient and fast cooling agent.
Although it is not expensive, purchasing it requires a declaration of intended use, because it is extremely dangerous to handle and can cause severe burns.
Shabbat Shalom 😊
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