Archives of Ask A Scientist!

About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 8 December, 2008 Next Week's Question
Are oil molecules afraid of water?
Why does oil float above water?

This question identifies an observable fact that we witness often in our daily lives. We know that oil floats on water from our personal experience - you can see pools of oil on top of a puddle after a rainstorm or in the kitchen sink while washing dishes.

Oil floats on water because of two factors: First, teaspoon for teaspoon oil weighs less than water. This makes oil buoyant in water, just like a cork or an air-filled rubber duckie stays on the water's surface in a bathtub or bucket.

Many, but not all, oils are less dense than water. You can demonstrate this by comparing the weight of a beaker of water with a beaker of oil. But that is not the end of the story, for example, most alcohols are also lighter than water, and they do not float.

What is the difference? Oil molecules are hydrophobic (from the Greek meaning fear of water). Most familiar oils do not dissolve in water, instead the molecules cluster toward each other and then float up to the surface. If a large amount of oil is poured into water, the oil will spread out and form a "skin" over the water. Oil laying on the surface of water changes the surface characteristics, such as, how the surface looks to the eye or how it reacts to disturbances like wind. And that's the source of the old saying about calming the sea by "pouring oil on troubled waters."