Thursday, May 11, 2017

Non-Obvious Causes

When we think scientifically, we are acutely aware of the cause and effect phenomenon. Causes are easy to observe in some cases. For other situations causes are difficult to observe without devising appropriate observational strategies. Before the Scientific Revolution empirical observations were not systematically utilized. At the onset of the Revolution implicit powers of men’s minds yielded to a greater dependence on evidence, both experimental and observational, and rational analysis. Formal science methodology achieved prominence during the Revolution along with a heightened awareness of cause and effect. 

Science experiments in our classrooms depend on traditionally accepted methodology. Some experiments are designed with the “wow factor” in mind in order to capture the attention of our young scholars. In this day of graphic displays of contemporary technological wizardry, we sometimes “sell” our science based upon how spectacular our science demonstrations are. They may be spectacular indeed.

Example 1: (I plead guilty of appropriating the “wow factor” on some occasions in my science classroom.) The “Egg in the Bottle” experiment is a classic science classroom spectacular. Air at sea level (most locations are somewhat above sea level) exerts a pressure of 14.7 lb./sq. in. If this substantial pressure is enlisted to push a hard boiled egg into an old-fashioned milk bottle without touching the bottle, we reap the “wow factor.” Observation of this classic experiment may help us determine a non-obvious cause after we observe a startling obvious effect.

The diameter of a peeled, hard boiled egg is larger than the the diameter of the mouth of the milk bottle. We could have challenged a student to push the egg into the bottle manually. He may have succeeded using considerable force, ruining the egg in the process. Our teaching challenge was to instruct students concerning the presence and strength of invisible air pressure. We must permit normal atmospheric air pressure to accomplish the task without our help..

The teacher folds a strip of newspaper and lights one end. He drops the burning paper into the bottle; the paper burns and is quickly consumed. Smoke pours out of the bottle along with heated air which expands out of the bottle. We quickly place one end of the egg on the mouth of the bottle. The egg almost immediately pops into the bottle followed by student “oohs” and “aahs.” After discussion students conclude there is less air in the bottle after the smoke and hot air air are expelled. Consequently, there is less air pressure inside the bottle than outside. Students conclude that the pressure of normal outside air pressure forces the egg into the bottle toward the now lower pressure. Discussion generates reminders that air always flows from a higher pressure to a lower pressure region. The egg obeys this “rule” of nature. The pressure differential does not have to be great for the experiment to succeed. Many students propose that the egg enters the bottle by “suction.” I respond, “Suction never did any work.” The egg is forced into the bottle from the outside, not from the inside. 

Example 2: The vacuum pump demonstration was another spectacular attention-getter and a wonderful teaching tool. A bell-shaped glass cover (the bell jar) on a platform is sealed shut and the pump motor started. Most of the air inside the bell jar is removed after a few minutes. When invisible air is removed we notice no obvious change. But when we place various objects into the bell jar and turn the pump on, we notice remarkable effects from the non-obvious cause: removal of air and subsequent lowering of air pressure.

A partially inflated grapefruit-sized balloon maintains its shape inside the bell jar before the pump was started. Air pressure inside the balloon is equal to air pressure outside the balloon. The air pressure forces of both air regions are balanced, but when air was removed from the outside of the balloon, the forces of air pressure inside and outside the balloon became unbalanced; the balloon began to expand. Outside air pressure was diminished—air inside the balloon remained the same. The ballon soon expanded from the force of air pressure inside the balloon, stretching the balloon to its breaking point.

Students are challenged to stretch the rubber of an uninflated balloon by hand to resemble its size and shape before the pump motor was turned on. They discovered that assignment is impossible. A little bit of air inside the balloon however, accomplishes the trick with the greatest of ease. Students determine that “a little bit of air” inside the balloon exerts an exceedingly powerful force in order to expand and pop the balloon. We need only to reduce the external pressure to visually observe the effect of internal air pressure.

Several other vacuum pump demonstrations became classroom favorites. One was expanding a marshmallow to many times its normal size. When we allow air back inside the pump, the marshmallow gives away its secret: it is filled with multiple little air compartments acting initially like little balloons. The marshmallow ends up tiny and shriveled. A somewhat more difficult demonstration to understand is “boiling cold water.” We boil tap water without raising its temperature. Lowering the air pressure permits water molecules to escape more easily. (Water molecules are always “trying” to escape.) The water molecules burst through the surface of the water more easily unimpeded by normal air pressure. The boiling point of liquids relates to both temperature and air pressure.

Many non-obvious causes in our world result in startling effects. The Creator of all things authored all physical laws of our universe. This authorship results in an incredibly ordered world. God, therefore, is not only the Creator, but also the Lawgiver. We rejoice in the love and omnipotence of our Lawgiver.