Tag Archives: Air

Bernoulli’s Principle Will Leave You Breathless!

What sorcery is this!? Science it turns out! This is a great example of Bernoulli’s Principle! In short, this states that moving air has a lower pressure. Imagine trying to dig a hole in a pool of water: as soon as some of the water gets moved out of the way, the surrounding water rushes in to take its place. Air does the same thing: whenever it moves, the lower pressure draws air in around it!

The cup and straw demonstration shows this nicely, and it’s also a great experiment to try at home! By taking each apparatus and blowing into it, we can see there is a pretty huge difference.

difference

Inside the cup, air is moving quickly. This causes a lower pressure inside the cup than outside, and air that tries to fill up the space suctions the balloon in place. Alternatively, the cup with holes in the sides allows the surrounding air to help out. Very similar to the Bernoulli Bag, nearby air joins in creating a larger column of air that can lift, and even suspend, the balloon.

bernoulli-loop

We know this looks like a trick, because it’s hard to tell from watching that he is exhaling vigorously in both cases. If you don’t believe us, definitely try it yourself!  Of course, it is possible to hold the balloon into the cup by inhaling, but it’s actually more difficult to suck up the balloon from a short distance away! The difference in pressure from blowing fast moving air into the cup is more effective at sucking up the balloon.

While Bernoulli’s Principle can be tricky to understand, it is very important! The fact that fast moving air has a lower pressure is one of the primary ways that airplanes are able to generate lift! The air going over the wing actually goes faster than the air below, which you can see in this very cool shot from a wind tunnel!

wing-wind-tunnel

Credit: Holger Babinsky, University of Cambridge

The Magic of Wind & Science!

What sorcery is this!? Science it turns out! This is a great example of Bernoulli’s Principle! In short, this states that moving air has a lower pressure. Imagine trying to dig a hole in a pool of water: as soon as some of the water gets moved out of the way, the surrounding water rushes in to take its place. Air does the same thing!

IMG_9574The cup and straw demonstration shows this nicely, and it’s also a great experiment to try at home! By taking each apparatus and blowing into it, we can see there is a pretty huge difference.

The cup without any holes in the sides actually holds onto the balloon, which is weird, but makes sense. Inside the cup, air is moving quickly. This causes a lower pressure inside the cup than outside, and air that tries to fill up the space suctions the balloon in place. Alternatively, the cup with holes in the sides allows the surrounding air to help out. Very similar to the Bernoulli Bag, nearby air joins in creating a larger column of air that can lift, and even suspend, the balloon.

WizardrySmall2We know this looks like a trick, because it’s hard to tell from watching that he is exhaling vigorously in both cases. If you don’t believe us, definitely try it yourself!

Blowing air through a straw makes a small amount of air move pretty fast. A leaf blower makes a lot of air go really fast! When we add the beach ball, this air rushes around it at high speeds, making a low pressure. Surrounding air is then drawn in from all sides, which holds the ball in place.

 

DiagramWhile it might look like this is just well balanced on a spout of air, this idea falls flat when the angle of the leaf blower is changed. In moving to this orientation, the science stays the same–rushing air still causes the surrounding molecules to rush in and offer support on all sides–despite it looking like magic to the untrained eye!SorcerySmall

Balloon Stabbing Science

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.

BalloonSkewer3

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!

BalloonSkewer4

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!

BalloonSkewer5

DIY Giant Air Bazooka!

This is one project that we had a ton of fun with, and it’s something you can do at home! Here is how we made our giant air cannon.

  • Lets start with the materials you will need.
  • Help from an adult. They will need something sharp.
  • A trash can or bucket, and permission to ruin it
  • Plastic sheet–such as a shower curtain, or plastic trash bags
  • Tape or bungee cords, or both!

shooting

This can be done with almost any size of bucket or trashcan. Larger containers will be more dramatic. Once you have made your selection, make sure the plastic sheets that you have are big enough to cover the mouth of the vessel. then…

Start by cutting a hole in the bottom right in the center. The perfect size for this depends on the size of the trashcan, with smaller ones needing a smaller hole. You are aiming for something between 2 and 5 inches across. Get an adult to help with this. Depending on the material of the trashcan, a knife, box cutter, or sawzall might be the best tool for the job.

IMG_2601Turn it over so the newly cut hole is on the floor. Stretch your plastic material over the large mouth of it, and attach it    with bungee cords. Ours still slipped a bit so we added some tape.

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Take aim! The bottom of the trashcan is now the muzzle of your giant air cannon! Fire it at your friends, or knock over stacks of cups by lightly smacking the plastic covering the opening! Have fun!

HappyZack

One interesting thing: Sometimes when you fire at something and miss by a little bit, it will get pulled backwards! This is because the air that you shot out is interacting with the air molecules around the room. Below is a cool animation of how the air gets stirred up when it goes through the room

Animation of how the air molecules interact when a pocket of air is shot through stationary air. Credit: William J. Beaty

Animation of how the air molecules interact when a pocket of air is shot through stationary air. Credit: William J. Beaty

If you can get some fog into the can, it will blow smoke rings! Looking at the animation above, you can see why the smoke rings form. The smoke is in the swirling red bits above. In two dimensions, this just looks like a couple of circles, but that is the cross section of a ring. As the smoke passes through the air, it spreads out a bit, leading to the rings you see below!

biggif

What does Liquid Nitrogen do to Balloons

Liquid Nitrogen is a cryogenic liquid. It seems exotic because its extremely low temperatures cause it to affect things differently than we see in everyday life. To understand it a bit better, lets look at where it comes from.LN source

Nitrogen is a very common element. It makes up about 78% of the atmosphere, so you are quite literally surrounded by it constantly. This can be surprising to some people, as we know that people need to breath oxygen. However, of every breath you take, only about one fifth of it is actually oxygen!

Air_Composition_Chart

Image from M7 Science.

Liquid nitrogen is simply this same gas, but cooled down until it became a liquid. There are three primary states of matter: Solid, liquid, and gas. Most elements can be found at any of these three states of matter. Which state of matter you find depends on two things: pressure and temperature. In chemistry, we have something called a phase diagram to help us visualize this idea. Lets look at one that is a bit more familiar. Here is the phase diagram for water.

Phase Diagram Water

Image from Pearson Education.

This diagram contains a huge amount of information. First of all, at sea level, we experience 1 atm of pressure. At that pressure, water freezes at 0℃ or 32℉ and boils at 100℃ or 212℉ as expected. However, large changes in pressure can change that a bunch! One unique characteristic of water is that at higher pressure, the freezing temperature actually gets lower. This is very important, as it means that our oceans and lakes will freeze on the tops and not at the bottoms! Another interesting feature of the diagram is the triple point. At this exact temperature and pressure, all three phases of matter can exist equally.

The phrase diagram for nitrogen is similar, except the temperatures are very different! At the same pressure of 1 atm, nitrogen freezes at -210℃ or -346℉ and boils at -196℃ or -320℉!

nitrogen-phase-diagram

Image from CHEMIX Chemistry Software.

As the balloons are dipped into the bowl of liquid nitrogen, they shrink rapidly. We have seen this before in several of our other blogs, where we talk about how temperature and volume are related. To summarize, when gases get colder, they take up less space. However, this is more dramatic than we have seen before!

Shrinkage

This is because we are taking a balloon filled with atmospheric air and subjecting them to liquid nitrogen. The nitrogen in the air gets cold enough that it starts to turn into a liquid! Liquids take up far less space than gases because the molecules are closer together. For nitrogen at room temperature, the same amount of gas takes up 694 times as much space as a liquid! Want another example? Here we pour hot water into liquid nitrogen. As the nitrogen instantly evaporates, it pushes around the water vapour to fill almost the entire room!

Cloud Boom

The Power of the Air!

 

How did the can get crushed? You could see in the video it wasn’t pushed in by the tongs, so what did it!? This very simple experiment works because of something called Charles’s Law. Charles’s Law says that a gas will get bigger if it gets hotter, or smaller if it gets colder, as long as the pressure doesn’t change.

One thing that you can’t see in the video is that the water in the can is boiling. This means that the can is full of water vapor that is around 200℉! Next, the can is placed open-side down into a container of cool water, probably about 50℉. Note that we aren’t changing the pressure, so Charles’s Law tells us what happens next. The cold water cools down the water vapor, causing it to contract (and even condense!), but this is not what really crushes the can. The real culprit….is air.

Can.jpg

Air doesn’t seem to weigh anything. We can’t see it, or pick it up and hold it in our hands very well. However, that doesn’t mean it is light! The atmosphere weighs a whopping 6,000,000,000,000,000 tons! The earth is pretty big, but that means that at sea level, there is about 15 pounds of air pushing down on every single square inch!

However, not everything gets crushed by the atmosphere. Your body effortlessly pushes back on the air to not get squished, just like the hot air in the can pushed out to keep the can from imploding. However, when the cold water cooled and contracted the air, there was nothing to push out against the atmosphere, and no way for the atmosphere to get in. So yes, the air just crushed it!

This is a great DIY experiment to do at home or try in class! It requires few materials, and can teach a lot of science! Charles’s Law is a very powerful idea, and is half of the Ideal Gas Law, which is seen in both chemistry and physics classes!

Note that this is the same principle that we used to get our egg into the bottle experiment!

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