December 2016:
After taking last month off of writing ChemShorts for Kids, I thought I’d add another little trick from the Illinois State Fair that Frank Salter shared with many attendees.
Materials:
- Coke bottle (or any bottle that narrows to the top but has a pronounced neck)
- A pen cap
Rest the pen cap inside the bottle at the opening as you hold the bottle horizontally. Although you can put the cap in either direction, most put it in such that the cap opening is pointed to the outside. Now try to blow the cap into the bottle. What happened and how do you explain it?
Although there is not much chemistry in the demonstration, it can be explained with a little physics called the Bernoulli Principle. This states that a slow moving fluid (air in this case) exerts more pressure than a fast moving fluid. As you blow into the very narrow opening, the air moves quickly around the cap and into the large opening. Since this is a confined space and the air must come back out again, the greater pressure is that coming from the slow moving air back out of the bottle.
Make a funnel out of a piece of paper and see what happens when you put the pen cap in the wider end and blow into the pen cap. Try putting the pen cap in the narrow end. Can you explain what happened here?
- Paul Brandt
To view all past “ChemShorts for Kids”, go to: http://chicagoacs.org/articles.php?article_category=1
