The Invincible Soap Bubble

My 5th grade daughter had to do a science fair project this year and after much deliberation, decided on this project called The Invincible Soap Bubble, found at All Science Fair Projects dot com.

I just thought it was one of the most visually interesting projects I’ve seen, so I thought I’d share it here:

Materials
• 5 plastic cups
• 100 mL liquid detergent
• 500 mL water, plus extra to add to lid
• 10 mL corn syrup
• 10 mL glycerin
• 10 mL lemon juice
• 10 mg sugar
• stopwatch
• air pump
• straw
• marker pen
• measuring beaker
• medicine cup
• round plastic lid

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Procedure:

1.  Using the marker pen, label the 5 plastic cups as “corn syrup”, “glycerin”, “sugar” , “lemon” and detergent only.

2.    Each cup is filled with 100ml of tap water. Another 20ml of liquid detergent is added to each cup and mixed with the water. Then 10 ml of corn syrup, glycerin, sugar or lemon is added to each cup and mixed once more.

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The cup marked detergent only is the control and it contains only a mixture of water and detergent.

3.    The lid is wetted with the extra water.  Then the straw is attached to the air pump and dipped into the solution briefly.  The pump will be pushed in and out and the bubble is blown to fill the lid.

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The stopwatch is started as soon as the straw is removed and it is stopped when the bubble pops.  Record how long the bubble lasts before it bursts.   Repeat this process for a total of 10 times.

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4.    Step 4 is repeated using the solutions in the other 4 cups and the times are compared to find the solution with the longest times.

When the science project is done, calculate the average times for each additive and make a bar chart.  Determine which bubble additive made the bubbles last the longest and the shortest.

Quick answer:  We found the additive which made the bubbles last the longest was glycerin.

Once the science project is complete, have fun playing with your new bubble solution:

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Why do bubbles have color?

From the website bubbles.org, we see that:

A bubble reflects color from its surroundings.

When a light wave hits the surface of a bubble, part of the light is reflected back to a viewer’s eye from the outer surface and part of the light is reflected from the inner surface which is a few millionths of an inch further. As the two waves of light travel back, they interfere with one another causing what we know as color. When the waves reinforce each other, the color is more intense. When the wave get close to canceling each other out, there is almost no color. As a bubble wall gets thinner, either from a weak solution or because gravity has pulled its chemical content to the bottom, the distance between the inner surface and the outer surface of the bubble becomes less and less until the two reflected waves of light start to coincide and cancel each other out. The result is that the bubble loses its color and can become nearly invisible.

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At what angle do bubbles join?

At Exploratorium.com we find that

Regardless of their relative sizes, the bubbles will meet the common wall at an angle of 120 degrees. This is easy to see in the bubble picture to the right. All three bubbles meet at the center at an angle of 120 degrees. Although the mathematics to prove this are beyond the scope of this article, the 120 degree rule always holds, even with complex bubble collections like a foam.

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Would you like to get your geek on and know the mathematical proof that 120 degrees is the correct answer?

Here you go:

http://pubman.mpdl.mpg.de/pubman/item/escidoc:150124:1/component/escidoc:150123/JoGA17-75.pdf

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And if this isn’t enough geeky bubble fun for you, you can take a look at Project Gutenberg’s eBook of C.V. Boys  SOAP-BUBBLES AND THE FORCES WHICH MOULD THEM.   He delivered this bubble physics lecture over three days in the theater of the London Institution on December 30, 1889, January 1, 1890 and January 3, 1890 before a live juvenile audience.

I love his dedication:

This book is dedicated

BY THE AUTHOR

AS A TOKEN OF ESTEEM AND GRATITUDE,

AND IN THE HOPE THAT

IT MAY EXCITE IN A FEW YOUNG PEOPLE SOME SMALL

FRACTION OF THE INTEREST AND ENTHUSIASM WHICH

HIS ADVENT AND HIS LECTURES AWAKENED

IN THE AUTHOR, UPON WHOM THE LIGHT

OF SCIENCE THEN SHONE FOR

THE FIRST TIME.

So, when is the last time your kids went to a physics lecture for inspiration?

At the very least, I encourage you to take a look at that eBook and see the interesting and detailed hand illustrations.

I think the next project we might try is experimenting with different shaped wire frames for experimenting with soap films (some designs of which were illustrated in C.V. Boys book).

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