Demo Science

Monthly Archives: August 2015

Light Bulb Air Currents

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Air is all around us, all the time (except underwater), and it’s always moving. Often, it’s too gentle for us to notice; other times, it can just about knock you off your feet. Horizontal air movement is, of course, wind, while vertical air movement creates an air current. We can “see” wind by the way it moves tree leaves, flying flags, and random debris. Visualizing air currents can be tougher, though these movements are just as important as wind to our weather.

With this handy dandy Demo Science science demo, you can explain what causes air currents and create a neat visual to go along with it. Who’s ready to science?

Powdered Donuts Lightbulbs Make Me Go Nuts

All you’ll need is a freestanding lamp with the lampshade removed, and a little bit of talcum powder. Six pounds or so should be just about right. This experiment will work better with an old-timey incandescent bulb instead of a modern compact fluorescent or LED bulb, so see if you can dig out one of those old dinosaurs from somewhere.

Start with the lamp turned off—it’s best to make sure it’s been off for a while, so it’s cooled completely. Leave the lamp off, sprinkle a light dusting of talcum powder over it from about a foot above, and see what happens. SPOILER

If this happens, you definitely did something wrong.

If this happens, you definitely did something wrong.

Clear the powder off the bulb and the surrounding fixture, then turn the lamp on. Give it a few minutes to warm up, then sprinkle it with talcum powder as before. What happens now? SPOILER ALERT: something will actually happen this time.

Magic? No—Science!

If all goes as planned, some of the powder will float in the air above the lamp, buoyed by the heat the light bulb produces. That heat, um, heats the air around the bulb, making it less dense and allow it to rise above colder, denser air that is not warmed by the lamp. Heated air becomes less dense because, when heated, its molecules (like those of nearly any substance) “expand” and move farther away from each other.

The process of warm air rising above colder air is called convection. Hot air goes up, cold air sinks into the formerly occupied space. The cold air, now closer to the heat source, will be heated and the whole process will repeat ad infinitum.

The greater the temperature difference between the cold and hot air, the greater the speed of the ensuing air current will be. Same goes for wind, but sideways. The direction in which wind blows depends on the relative location of hot and cold air masses.

Photo credit: uLightMe / Foter / CC BY-NC-SA

The Moon is Bleu Cheese, Earth is Cheddar

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The ongoing shenanigans in our planet’s crust are responsible for earthquakes, volcanic eruptions, the creation of mountains, and various other literally Earth-changing events. But even the most in-depth television or online coverage of such events can’t really illustrate the fractures in the earth’s crust that make these things happen.

You could build a giant, drill-nosed tunneling vehicle, a la the bad guys in the late ‘80s Ninja Turtles cartoon and take an underground journey to view a faultline in person. Or, you could use cheese. Both are good, but we’re not mechanical engineers over here, so we’re only going to show you the cheese demonstration.

Cut the Cheese…for Science

For this quick and easy Demo Science science demo, all you’ll need is some pre-sliced cheese and a cheese cutting device of some time. For the former, we suggest something simple like cheddar, since smelly little kids like the ones you’re likely performing this experiment with wouldn’t know good cheese if you stuck it up their noses, and there’s no point in wasting more exotic stuff. (That’s not a knock on cheddar, though—cheddar is the longtime MVP of the cheese game.) For the latter, we recommend a little-known gizmo called a “knife”, but do what you like.

Piles of delicious science.

Piles of delicious science.

Gather your students (or whoever) around and bust out your first slice o’ cheese. If you’re using the kind of cheese that comes in individually-wrapped slices, remove the plastic film before continuing. Then, with your cheese slicing device, make a small cut in the middle of the slice, parallel to two sides and perpendicular to the others. (Cut straight, not diagonally, basically.)

Grasp the edges of the cheese parallel to the cut, and pull them gently in a direction perpendicular to the cut. Tell your students to observe the shape of the fracture (cut) as it grows, and keep pulling slowly until the cheese in torn in twain. If anyone (probably Kevin) wants to eat the jankety, ripped up, manhandled deskcheese, let ‘em. #wastenotwantnot

Make two cuts in a fresh slice o’ cheese, approximately one inch apart, in the same direction, parallel/perpendicular to the squared edges of the slice, and diagonally offset from each other. (But don’t cut diagonally—again, straight cheese cuts.)

Then, repeat the previous cheese ripping process. Observations will be different this time, as the tips of the two separate fractures grow past each other. Barring some sort of weird cheese anomaly, the fractures will begin to curve toward each other and eventually consolidate into a single, jagged fracture.

Continue the process as many times as you want and/or as many times as your students will tolerate before going all little-kid-ADD on you. Handing out pieces of cheese as you go will help keep them interested as long as possible.

The Cheese. Stands. Alone.

Your cheese ripping adventures are more or less analogous to tension fractures in Earth’s crust. Pulling on the edges of the cheese slice simulates the tensional tectonic forces that tear at our planet’s mantle far below the surface.

Wherever there is an imperfection or weak spot in the Earth’s crust (or a cut in a slice of cheese), this tension cannot pass through it and instead becomes concentrated around the tips of the break, increasing as the fracture grows. Increased tension makes it easier for the fracture to expand. When the twin cuts in the second round of the demo curve toward each other and combine, it is because tension cannot be transferred in a straight line across the space betwixt the two.

Real-life, deep-in-the-earth tension fractures lead to earthquakes, and similar action can be seen in larger cracks in glaciers and, on a smaller scale, in damaged asphalt roads.

Photo credit: ♥braker / Foter / CC BY-NC-ND

Ad & Co: The Hesion Brothers

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Everybody knows adhesion. Adhesion is everywhere. You’ve probably got a roll of adhesive (word derivation FTW!) tape somewhere in/on your desk right now, I’d wager. Cohesion is another story—almost everyone’s seen it in action, but most folks probably don’t realize it. This handy dandy Demo Science science demo will help your smelly students better understand how both ad- and cohesion work. To the Sciencatorium!

The Ol’ Tube-In-A-Tube Trick

For this experiment, you’ll need one medium to large test tube, one small to medium test tube that fits inside the larger one, water, and something in which to catch said water, as you’ll be deliberately spilling it all.

Make sure your test tubes are clean (as an aside, I know some industrial brush manufacturers who can hook you up if you’re in the market for test tube cleaning brushes), and that the fit is a fairly close one. You don’t want them sliding directly against each other, but you don’t want the smaller one bouncing around freely inside the larger one, either. You may want to do some pre-testing to see which size combo works best.

You, performing this experiment. Take it down a notch, bro.

You, performing this experiment. Take it down a notch, bro.

Once you’ve got your test tube size ratio squared away, gather your students (or whoever you’re demonstrating this jazz for) ‘round and fill both tubes with water. Hold them over whatever water catching device you’ve got, and slowly lower the smaller test tube into the larger one. Let go of the smaller tube—it will kind of sink and kind of float, but that’s not the important part here.

Then—just follow me here—invert the larger tube. Turn the whole thing tuckus over teakettle. The water will pour out, obviously, but if everything works out like it should, the smaller tube won’t fall out of the bigger one.* So, did you just become a wizard? No, silly—it’s adhesion and cohesion!

Please Explain to My Brain

As the water dumps out of both test tubes, the smaller tube will kinda sorta “rise” up in the larger one and, ultimately, stick to the inside, glass to glass. This is due to a combo platter of adhesion and cohesion.

Water molecules are polar, and their polarity attracts them to each other, forming beads (or drops) and creating surface tension. This intermolecular force is cohesion, and it occurs when like molecules or materials are attracted to each other.

Adhesion is a similar force that works between different types of molecules. Here, those would be the molecules of water and test tube glass. The combined power of cohesion and adhesion is stronger than that of gravity (in this case, anyway—it certainly wouldn’t work with a Buick in one of those giant shipping containers) and thus prevents the smaller test tube from falling to its doom.

* CYA statement: This is totally on you—Demo Science assumes no responsibility for broken test tubes. That’s the cost of science, baby!

Photo credit: practicalowl / Foter / CC BY-NC

Craters Gonna Crate

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So, craters, right? The Moon is covered with ‘em, as are several of the planets in our solar system and their moons. Heck, the entire Gulf of Mexico is essentially one big crater from the asteroid that killed off the dinosaurs. But not all craters are created equal: those on the Moon are jagged edged, with scattered debris betwixt them; those on Mercury are comparatively neat and tidy, with smooth edges and smooth ground between impact points. ¿Por que?

A (relatively) new crater on the Moon.

A (relatively) new crater on the Moon.

Go Big (Craters) or Go Home

The original version of this science demo called for a cereal bowl, spoon, soil, and water. It worked perfectly swell that way, but we at Demo Science wanted to make it more interesting, so we scaled up. With our version, you’ll want to do the experiment outside.

Instead of a bowl, use an old cast iron bath tub (or find a company that can fabricate a deep drawn stamping and have them make you a new one). Instead of a spoon, get yourself a shovel. You still need dirt and water, just more of each. Also, you’ll need a ladder and a small bucket (a gallon or less). And, if possible, a roof you can readily climb up on (like the one of the school where you teach, perhaps).

So: fill your tub roughly halfway with soil, then add some water and stir up the whole mess. Add more water (or dirt), as needed, until you’ve got a good mud going—it needs to be thin enough to drip and flow easily, but thick enough to have some weight behind it. “Sloppy” is the perfect consistency to shoot for.

Fill your bucket with mud, then smooth out the surface of your tub o’ mud as much as possible. Then, ascend that ladder, good sir or ma’am, with your bucket o’ mud and shovel. If possible, climb up on the roof. (Obviously, your mudtub should be set up by the side of the building in this case.)

From atop your ladder (or rooftop), scoop out a good bit of mud with your shovel, then hold it flat over the tub. Tilt the shovel slightly so the mud slides off and splatters into the tub below. Repeat your mud splattering process until the bucket is empty, moving your shovel over the tub to create mud “craters” in different places on the tub’s surface.

Clamber back down, then inspect the craters with your students. What sees ye?

Mercury's Debussy Crater

Mercury’s Debussy Crater

It’s Crateriffic!

A whole bunch of different craters of different sizes, that’s what! As the dripping mud hits the muddy surface in the tub, both the dripped mud and the surface mud will splatter. Gravity pulls these splatters down again quickly, where they create smaller craters of their own.

The falling mud has roughly the same effect as meteorites or asteroids striking the surface of a celestial body (albeit with much less force). When large meteorites hit a planet or moon, the impact instantly generates incredibly high temperatures, which melt the materials on the planet’s/moon’s surface. These liquefied materials splatter upward and outward, just like the mud in your tub.

All your “craters” will have roughly the same splatter pattern, and the surface of the tubmud will be not exactly uniform, but more or less the same across the board. As mentioned above, however, the craters of the Moon and Mercury (as just two examples) are wildly different. This is due to the varying gravity of different celestial bodies—Mercury has a strong gravitational pull, so material from asteroid impact splatters is pulled back to the surface quickly, resulting in minimal “splashed out” secondary craters; the Moon, however, has far lighter gravity, so splattered materials fly higher and spread out more, creating not only secondary craters but also high, jagged rims around the craters themselves.

Moon Photo credit: NASA Goddard Photo and Video / Foter / CC BY
Mercury Photo credit: Lights In The Dark / Foter / CC BY-NC-SA