CAUTION: This experiment uses dry ice (-109˚F) and liquid nitrogen (-321˚F). Proper safety equipment should always be used when handling these substances.
Physics tells us that pressure, volume and temperature are all linked when talking about gases. So what does this have to do with solid carbon dioxide (dry ice) and liquid nitrogen? When dry ice is placed into a balloon at room temperature, which is then tied off, it will start to warm up.
Since the ambient air temperature is roughly 65˚F, the air that surrounds the balloon is more than 150 degrees warmer than the dry ice! This hug difference adds energy to the dry ice turning it into gaseous carbon dioxide through the process of sublimation. Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.
Now that there is a balloon full of carbon dioxide gas we can cool it down with something colder than dry ice. This is where liquid nitrogen comes in. The balloon gets dunked into a bowl full of the -321˚F liquid! Cooling the gas in the balloon down means that it loses energy making the molecules start to clump, making the balloon lose volume. It will turn the carbon dioxide gas back into a solid through the process of deposition. Deposition is basically the opposite of sublimation, turning the gas directly into a solid.
This process of cooling and warming to change the balloon’s volume can be repeated over and over again. Or, with the inflated balloon, dunk it in the bowl of liquid nitrogen, take it out, and before it can expand again, rip it open to see the solid carbon dioxide for yourself!
Try out this easy DIY science experiment at home. All you need is a balloon, a penny, and a hex nut. Place the penny or hex nut in the balloon, blow it up and then tie it off. It’s as simple at that! Now give your balloon a good spin and make some observations. Try using many of your senses for this one, but maybe avoid tasting it.
The penny races around and around with little sound, and it takes a really long time to stop spinning. This is due to something called the centripetal force and the conservation of momentum. Centripetal force is the force that makes something continue spinning if it is already in a circular path. It is a force that constantly pulls an object towards the center of its path. Newton’s first law states that an object in motion tends to stay in motion and an object at rest tends to stay at rest unless acted upon by an outside force. In the case of the penny that is constantly spinning in the inside of the balloon, it wants to continue moving. However, if the centripetal force did not exist then the penny would want to travel in a straight line and slam into the inside of the balloon, causing it to come to a crashing halt of motion.
The hex nut also has a centripetal force on it, however the biggest difference between it and the penny is that the hex nut makes a ton of noise. The noise actually comes from the fact the the hex nut has sides. Those sides attribute to more friction which causes vibrations on the balloon. Those vibrations are turned into sound waves, which is the noise that you here. What do you notice as you increase or decrease the rate of rotation of the hex nut? You should be able to notice a definite difference in volume level as well as pitch. If you spin it faster it should get much louder and at a higher pitch. This is also true for other things like vocal chords. The faster that you pass air along them, the higher the pitch will get. What other things can you think of to put inside of your screaming balloon? What differences can you observe?
How does this balloon stay intact? It’s got everything to do with our angle of attack.
Latex, the stretchy material most balloons are made of, is a polymer. Polymers are made of macromolecules, or long chains of repeated small parts. When a balloon inflates, the long molecule chains in its surface stretch out & make room for the air collecting inside.
The balloon isn’t stretched equally in all directions, though. It experiences less tension in two places: the knot at the bottom, and the point directly opposite the knot. You can usually see this point as a dark spot on the top of the balloon. These areas of least stress are ideal targets if we want to stretch the latex out even more…by stabbing it with a skewer, for instance!
Once the surface has been punctured, the polymer stretches tight around the skewer, keeping the air trapped inside the balloon. We coated our skewer with dish soap to make it more slippery and to help seal the gap between skewer and latex.
It’s important to be gentle during the stabbing process– stretching the polymer too much will cause those long molecule chains to tear, popping the balloon! It also helps to twist the skewer slowly as you break each surface (remember to aim for the dark spot at the top of the balloon on your second puncture). A careful touch, a little patience, and, you, too, can have a balloon kebab!
The balloon in the video isn’t anything special. It’s a completely normal balloon filled with completely normal water. However, water is quite extraordinary!
We describe matter by listing its different properties. Some of these properties include how dense something is, its flexibility, its ability to conduct electricity, and even its color! Another less commonly known (but just as important!) property is called “specific heat”. This property is one of the things that makes water really interesting!
Specific heat indicates how difficult it is to heat up or cool down an object. For example, if you were to put two pots on a stove and fill one with air (by leaving it empty) and fill one with water, the air one would heat up much quicker even though the stove is adding the same amount of energy to each one! The water doesn’t heat up nearly as much while being given the same energy, meaning it has a very high specific heat.
This is exactly what happens in the video. The match is hot enough to melt the rubber and form a hole, causing the balloon to pop immediately! It actually pops before the fire even reaches the surface.
With the water balloon through, the entire balloon can be engulfed in flame, and nothing happens! This is because the water absorbs the energy from the hot flame, but doesn’t heat up very much. The rubber never heats up enough to melt.
Specific heat works the other way too. Water also takes a long time to cool off. In this way, the specific heat of water actually shapes the climate on a global scale. Take a look at the image below. The snow cycles are much more visible in the Northern hemisphere because they only have to go over land. Ground has a lower specific heat than water, so during the winter it cools down more easily, allowing the cold to pass further south forming ice over most of the Northern continents. In the Southern Hemisphere, the water is much more difficult to cool down, and the icy chill barely even reaches the land!
“A Breathing Earth” by John Nelson, using images from NASA’s cloud free satellite imagery of Earth.
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