Tag Archives: Clouds

Make Your Own Cloud Chamber

Clouds usually form when water molecules clump together on small particles of dust in the air. These particles are called condensation nuclei. In clean air, they’re hard to come by, so clouds don’t form easily. If conditions are very humid, the air can become supersaturated, or rich with water molecules that would form a cloud if condensation nuclei were available. With nothing to grab on to, though, the molecules stay suspended and invisible… that is, until something disturbs the system.

StJohnFisherCollege contrail Image courtesy of St. John Fisher College.

You’ve probably seen this happen before! Jet planes leave contrails, or condensation trails, when they introduce exhaust into supersaturated areas of Earth’s upper atmosphere. RochesterDecayThis is a common example of foreign particles triggering condensation. Air molecules themselves can also act as condensation nuclei if they’re electrically charged. One way that air molecules become ionized (or charged) is by colliding with radiation from outer space.

Earth receives a constant shower of cosmic rays. Most primary radiation that reaches our atmosphere comes in the form of ultra-high-energy protons, followed in frequency by helium ions and a smattering of other particles. These decay in the upper atmosphere into elementary particles, which go on to ionize thin streaks of the lower atmosphere as they continue hurtling Earthwards. In a supersaturated environment, the newly charged air molecules act as condensation nuclei, leaving a cloudy trail in the wake of the decayed cosmic radiation. The image at left (courtesy of the PARTICLE program at Rochester University) shows primary rays decaying into pions, muons, neutrinos, and gamma rays.

Below, a streak of mist reveals cosmic radiation as it travels through our tabletop cloud chamber. To see cosmic rays for yourself, you’ll need a contained, supersaturated vapor and a bright light source to highlight cloud trails. Science Friday has an excellent step-by-step instruction set that helped us a lot in our DIY design process– check it out!

CloudChamberGif

Written By: Caela Barry

Into Thin Air: CO2 Science

Carbon dioxide, or CO2, is one of the handful of compounds that most people are familiar with. People and animals breathe it out, plants love it, and we make a lot of it, which probably has some consequences. We are going to look at this well known gas in its solid form and hopefully answer any questions that come up along the way!

bigbubbs croppedSolid carbon dioxide is more often referred to by the name dry ice. This is because it never leaves behind a wet spot when it disappears. Unlike water, which will melt to a liquid naturally under normal conditions at room temperature, dry ice will instead skip to a gas. To the left, you can see dry ice under water releasing bubble after bubble of transparent carbon dioxide gas. This physical transition from a solid to a gas is called sublimation, and isn’t anything to be afraid of. Its just the less familiar cousin of evaporation and condensation. For more on that, check out this blog.

Here, we put our dry ice in a bowl of warm water. Water is constantly evaporating, and this warm water is no exception. As a result, the air above the water is very humid as it contains a lot of this evaporated water. One important thing about dry ice that hasn’t been mentioned yet: it’s cold. Like -109℉ cold. Brrr!

Adding it to the water causes air temperature to drop, forcing the water vapor in the air to condense. If it looks like fog, that’s because it is! We have simply made a low-flying cloud in a bowl! Clouds in real life form the same way. Warm air carries water vapour up into the high, cold parts of the atmosphere where they condense in the same way, minus the dry ice, of course.

The cloud forming is independent from the bubble expanding. This is a bit tricky. As the water vapor cools down and condenses it is not pushing out on the bubble. However, the dry ice is sublimating. the resulting carbon dioxide gas takes up more space. Unfortunately, CO2 is colorless. This makes it look like the cloud is blowing up the bubble, but really the cloud is just filling up the space that the sublimated dry ice is clearing out for it, until…

burst my bubble

The bubble bursts and the dense cloud falls to the ground, which looks really cool. It also raises a rather interesting question: If clouds are more dense than air, then what in the world are they doing way up there in the sky? The answer is a bit complex. The short version is that the tiny water droplets that make up clouds fall very slowly, but they tend to form in warm, rising, low pressure air that overcomes their slow fall, allowing them to float high in the sky.

clouds1
For more information, I recommend reading this article.

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