Tag Archives: Chemistry

The Power of 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!

DIY Science Experiment: Egg in a Bottle

You might be asking yourself why you would want to put an egg in a bottle. The answer is, of course, for science! This is a great experiment for explaining the basics of the ideal gas law. Mainly, that gases expand and contract when they change temperature. Here we will explore how to actually do the experiment, and what the science is behind it.

Materials:

  • Peeled hard boiled eggs. Note that if they crack during peeling, they will likely not survive the ordeal!

  • Bottle with a neck smaller than the egg. Erlenmeyer flasks work great!

  • Matches, or a small piece of flammable material

  • Workspace clear of burning hazards

That’s it!

Doing the experiment:

  • Read the steps first. They have to happen quickly!

  • Light a match or something small and flammable. A small piece of paper works great!. In the video, we use four strike-anywhere matches.

  • Drop your flaming object of choice into the flask. With matches, do it quickly! If you wait too long, there wont be enough fire to heat the air!

  • Put the egg on top of the flask so it completely covers the opening. This must be done quickly

  • Watch!

You should see the fire go out and the egg get sucked into the bottle shortly thereafter.

What happened?

The fire rapidly heats the air in the flash. Then, the fire should quickly become starved of oxygen and go out. Once the fire stops and the air begins to cool. The molecules in the gas slow down as it cools, decreasing the pressure inside the flask. The air pressure outside is then greater, and pushes the egg down the seemingly-too-small neck of the bottle. Because the air pushes equally from all sides, the egg stays intact, unlike if you had done it with your hand!

How do I get it out?!

There are three good ways to do this.

  1. Get something pokey, like a butter knife, and chop the egg into bits and dump it out. Messy. Not my favorite.

  2. Blow in behind the egg (like in the video–note, we shook the matches out first for safety). The hot air on your breath should be enough to push it out.

  3. Flip the flask over so the egg covers the opening from within. Run hot tap water over the base of the flask. As the air inside heats up, it pushes the egg out, simply doing the experiment in reverse!

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