Saturday, April 26, 2008

Something Educational!

I used to regularly post links to websites, experiment ideas, etc, and get positive feedback from people that they found it interesting.

I think between our autonomy and our busy lifestyle, I've got out of the habit of doing that.

So, to remedy it, here is something educational!

Robert Krampf's Experiment of the Week
Why Things Go Bang!
Video: Why Things Go Bang

Most sounds are caused by vibrations, but think about the sound of a firecracker going off. Now think about lightning, popcorn, and explosions. All of them make sudden, loud noises, and all those sounds are the result of air getting bigger. That's right. Just air getting bigger.

To explore that, you will need:

a balloon
something with a sharp point
one of the plastic canisters that film comes in (You can also use a plastic pill vial, with a snap on cap. Don't use one of the child-resistant caps, because it won't work.)
baking soda
tissue paper

First, blow up the balloon. What is in the balloon? Air, right? The air in the balloon is being squeezed, making it smaller than it usually is. If we let the air out of the balloon, it will get bigger, expanding to its original size. If we let the air out slowly, it expands slowly, and does not make much noise. On the other hand, if we took something sharp, like a pin, and made a hole in the balloon, it would rip, letting the air get bigger very quickly. As the air expands, it pushes the air around the balloon out of the way. That air pushes on the air beside it, which pushes on the air beside it, causing a wave of pushed air to move out in all directions. When this wave of pushed air reaches your eardrum, you hear a loud sound. The more the air expands, the bigger the push and the louder the sound. Ok, you can pop the balloon now and hear it for yourself.

Another way to see that the bang is caused by expanding air is to make a pop with a plastic film canister. Take a small piece of tissue paper and put about half a teaspoon of baking soda into the center. Fold the sides in and twist it to make a small package that will contain the baking soda and is small enough to fit easily into the film canister. Put about a teaspoon of vinegar into the canister. Have the lid ready. Drop the packet of baking soda into the vinegar and quickly put on the lid. Stand back and watch. After a second or two, the cap will fly off the canister, with a loud pop. Try it again, without the lid. Does it make a pop?

When you mix vinegar and baking soda, they give off a gas called carbon dioxide. That is what makes all the bubbles. With the cap on, this gas is trapped inside the canister. As the chemical reaction makes more and more gas, the pressure builds up. Soon, the pressure is enough to pop off the cap, letting the gas expand suddenly. That produces the push to make the wave that your ears hear.

The same idea applies to firecrackers, lightning bolts, popcorn popping and many other sounds. They involve gases expanding very suddenly, producing the wave and causing a bang. You can even hear a sound from the expanding gases when you open a can of soda, and from the tiny pops of the bubbles in the foam popping. That sounds like a nice experiment for a warm spring day!

Have a wonder-filled week!


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Copyright © 2008. Robert Krampf's Science Education

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