© 2019 by Pernille Dahl & Cole Robbins. 

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Bubble Marker

Parts needed:
  • 1 Baseboard, 1x2, 8”

  • 1 Hobby motor

  • 1 Battery, C, or D

  • 1 Clothespin, spring type

  • 3 Wires, thin with insulation

  • Aluminum foil

  • 1 Piece of plastic from bottle or cup

  • 12" Wire, baling

  • Yarn or pipe cleaners

  • Bubble solution:

    • dish soap (Dawn and Joy seem to work well),

    • water (soft water is reputed to work better)

    • glycerin if you can find it helps but is not necessary

  • 1 Pie tin or bowl for bubble solution

Extra Tools: 
  • Wire strippers

  • Black tape

  • Drill

  • Nail bit

Project Description:

  1. Glue the motor onto the end of the 1x2 board so that the shaft sticks out over the end.  Strip two wires at both ends and connect them to the motor.  Shape the bubble loop out of baling wire.  Double it back where it will connect to the board so that it can’t twist easily.   

  2. Glue and/or tape the wire loop onto the board so that the loop stands around two inches from the tip of the motor shaft.  Strip one more wire at both ends. Wad aluminum foil around one end of this wire and one of the wires coming from the motor.  Tightly tape these aluminum foil pieces to the ends of the battery. 

  3. Make a 2 inch long strip of aluminum foil and pinch one of the remaining two wire ends to the end of the strip.  Wrap the strip around the tip of one handle of the clothespin and glue it in place.  Be careful not to get glue on the bottom side of the foil, where it will make contact with the wire.  Wrap the remaining wire around the other handle so that it will contact the foil when the clothespin is squeezed. 

  4. Glue the clothespin to the center of the board where it will be easy to press it.  Glue the battery to the end opposite the motor.  Wrap yarn or pipe cleaners around the bubble loop in order to soak up more bubble solution.

  5. Draw angling lines around a plastic bottle and cut out a section for the propeller.  The curvature of the bottle will create the bend necessary in the propeller, but you can always bend it a bit more or less.  Cut a glue stick piece about 1 inch long.  With a nail bit, drill a hole into one end of the glue stick piece.  Glue then tack the propeller onto the other end.  Your bubble maker should be working.  Check to see that the propeller is blowing toward the soap ring.  If it is blowing the wrong way, reverse the wires to the motor or the battery. 

  6. Make your bubble solution in a bowl or pan.  Dip the loop into the solution and get a bubble stretched across the loop.  Press the clothespin to blow a bubble up.

More to think about and try:

  1. How could you change your device to make larger bubbles?

  2. How could you change it to make many smaller bubbles?

  3. What would happen if you connected two batteries on the bubble maker?

  4. Are there any connections between bubbles and planets?

Concepts:

  1. Soap bubbles in air are made up of a thin layer of liquid surrounding some air.  The vivid colors you see in a bubble are the result of light rays interacting with the thin layer, some passing through, some reflecting and some interfering with each other. ­­

  2. Bubbles floating freely in air will always form a sphere.  This is the shape that results naturally from a thin surface layer pulling evenly in all directions. 

  3. The layer of liquid defining the bubble is evaporating quickly, and in the end it gets too thin to support itself.  You can see the bubble change thickness, because as the thickness changes, the colors change. 

 

 

A little Background:
 

It is truly astonishing how much science is present in a common soap bubble.  If you’ve gone to the trouble to make some soap solution and this little project, I hope you spend some more time fiddling around with bubbles. 

 

These bubbles are made of three substances:  Water, soap and air.  Water has a relatively large surface tension.  This means the molecules of water stick tightly to each other.  Thanks to this stickiness, you can get a paperclip to rest (not float!) on the surface of water.  Use a fork to place it in very gently.  The molecules of water cling to one another stronger than the force of the paperclip attempting to push them apart and fall through.  You can see this surface tension also if you place a drop of water on the table.  The drop will remain in a domed form, which means again that its molecules enjoy their own company more that that of the molecules of the table. 

 

Air is what the bubble is blown with, so to speak.  With a straw, you can blow bubbles in plain water, but they will usually rise directly to the surface and pop.  Without soap, the surface tension of the water is too strong to allow a bubble to remain at or above the surface of plain water.  (In the International Space Station bubbles of varying thickness were made of pure water.  Gravity it seems does not aid the formation of bubbles.)

 

To get a bubble out of water you need to sustain a tiny layer of liquid.  Scientists call this a thin film.  When you put soap into water, it organizes the water molecules in such a way that thin films can form and bubbles can exist.  Explaining this requires some fairly complicated chemistry, but here’s the basic story.  Soap is useful because dirt and grease are attracted to one end of the soap molecule and water to the other.  In this way soapy water can go into a fabric, grab the dirt and then get rinsed out.   In a soap film, the soap molecules are all lined up in parallel on the two surfaces of the film with the water-loving ends toward the inside of the film, and the dirt-loving ends toward the outside.  Between these surfaces is a bit of water. 

 

DRAWING

 

In this project you get a thin film stretched across the wire circle.  Essentially you have a captive segment of a bubble to examine without worrying that it will blow away.  Before you start blowing on it, check out the colors carefully.  You may recall that a rainbow’s colors result from white light being separated into colors by the process of refraction within a raindrop.  This is not that.  This is an entirely different phenomenon called thin film interference.  You can also see it sometimes in an oily puddle.

 

The thin film of a bubble wall acts as a two-way mirror, allowing some light to pass through while reflecting some light.  You can tell it reflects light, because if it didn’t, you couldn’t see it.  And you can tell some light passes through by shining a flashlight or laser pointer on it.  The interference arises from the portion of light that passes through the first wall and then gets reflected back by the second wall.  Some of this light makes it back out the front surfaces of the bubble. 

 

DRAWING

 

So, there are two sources of light coming back out the front of the bubble:  one bit of light that reflected directly off the front surface of the thin film, and one bit that went into the thin film, reflected off the inside back surface, and came back out through the front surface.  These two bits of light come to your eye together.  Sometimes they add up to reinforce each other and sometimes they cancel each other out.  Which happens depends on the thickness of the bubble wall and the wavelength of light.

 

The bubble wall is as about as thin as a few wavelengths of light (400 to 800 nanometers, or about a thousandth of a millimeter).  White light, which we get from the sun and most light bulbs, contains all the wavelengths of light.  As the light interacts with the bubble wall as just described, certain wavelengths that fit exactly within the thickness of the bubble wall get cancelled, while other wavelengths get reinforced.   The colors you see in the bubble then are composed of all the wavelengths of light that were not cancelled out. 

 

When you connect your battery to blow on the bubble segment stretched across the loop, its surface area and size increase.  Sometimes you can seal it off with a flick of the wrist and disconnect the device from the film to leave a floating bubble.  The shape of things like bubbles are described in the area of mathematics called topology.  Topologically speaking, a hollow sphere is an important shape.  It has two sides – inside and outside – but no edges.  The bulging bubble you were blowing before you sealed it off had two sides, but also had an edge defined by the wire.  You may have noticed that most planets and stars tend to be spheres just like bubbles.  It is a different effect – gravity pulling inwards on all things results in a spheroid – but a similar situation: in both cases a sphere is the shape that minimizes the energy of the total system. 

 

Some factors in making larger bubbles are a good bubble solution, patience and finesse, and moving the bubble ring so that the bubble itself doesn’t have to move much.  To make smaller bubbles you need a smaller loop and some mechanism to seal each bubble off before it grows too large.  Two batteries would make the motor go faster making the propeller blow harder and, with some ingenuity, perhaps making more bubbles faster.

Questions:

  1. How could you make the tornado spin faster?

  2. How can you make it spin slower?

  3. What would happen if you put the spinner and lid on a big bottle?

  4. What is the path of a little piece of water in the bottle as the tornado is spinning?