Giant Bubble Experiment

How Does It Work

Bubbles form because of surface tension of water that comes from atoms attracting each other. Hydrogen atoms (a negative charge) in one water molecule are attracted to oxygen atoms (a positive charge) in another water molecule. They like each other so much that they cling together and don’t want to separate. This causes “surface tension” which allows some insects to “walk” on water and paper clips to float on it. It’s just the water molecules clinging to each other electrically and providing a “surface” on the water.

The bubble solution is mostly water, of course, but the dish soap is a vital ingredient. Strangely, soap molecules chemically ruin surface tension but in so doing, they stabilize water molecules so that they can easily move and “stretch” into a spherical shape. Without soap, bubbles would be destroyed as the water molecules quickly link back together (try blowing long-lasting bubbles in plain water). Soap molecules also reduce evaporation on the surface film of the bubble. It’s evaporation that pops a bubble faster than almost anything else.

So, why do bubbles usually come out as round? Physicists will tell you that bubbles “enclose a maximum volume of air with a minimum amount of surface area” and a round surface does that with the least stress. Nature isn’t lazy, just smart. A water drop, a bubble, and the Sun are all nearly perfect spheres (the Earth is slightly fatter around its equator than it is from pole to pole so it’s “spheroid” or “like” a sphere). A sphere has the smallest surface area for the volume inside it which means the soap film can be the same thickness over its entire surface. It’s a very stable shape.

When you stuck your dry hand into the soap film of the bubble wall, it instantly popped. Oils, dirt particles, and other goobers on your skin broke the bonds of the film and it disappeared. When you coated your hand with bubble solution first, the oils on your skin were covered and the film of the bubble wall clung to solution and not your skin. The film didn’t break up as easily.

Take It Further

About the Ingredients

Water – The single most important part of the bubble solution is the water. Good quality water that does not contain high levels of iron, minerals, or purification chemicals is best. If you’re uncertain as to the quality of your tap water, invest in distilled water from the grocery store and use a smaller wading pool or container.

Soap – When it comes to dish soap, Dawn^®  just seems to work the best for homemade bubble solutions. Of course, a scientist will test a variety of other kinds of soaps to make sure. You’ll want to avoid using dish soaps that contain antibacterial ingredients.

Glycerin – Glycerin is the secret additive that gives a bubble extra strength because it slows down evaporation. Good quality glycerin can be pricey. Remember, you only need a small amount. (Note: Some bubble recipes suggest substituting clear Karo Syrup^® for glycerin.)

A bubble’s worst enemies are oil and dirt and gravity. A bubble will usually bounce off of a surface  free of oil or dirt particles that would normally cause a break in the thin soap film of the bubble. The problem with gravity and evaporation is that, due to gravity, the water film gets very thin (down to a millionth of an inch) on the top surface as time passes. It finally gets too thin to hold onto itself and the wall collapses completely.

Similar to the way we perceive the colors in a rainbow or on an oil slick in water, we see colors on a bubble through the reflection and the refraction of light waves from the outer and inner surfaces of the water layer in the film. The rainbow colors and dark lines you see on the bubble are the result of how the wavelengths of light are mixing after they leave the bubble. You can’t “color” a bubble since its wall is only a few millionths of an inch thick and the water layer between the soap layers is only a few molecules of that. A bubble will also reflect light and colors from its surroundings.