Science on a budget

Published 12:00 am Thursday, February 17, 2005

We've all heard old adages such as "what goes up must come down"; "if a trees falls in the forest and no one is there to hear it, does it make a sound?" and "the sky's the limit".

The scientific world of gravitational constants, sound travel and rockets firing into space seems more or less like science fiction to many of us.

But it is scientific fact for Jim Jernigan's students at Fort Dale Academy. In his physics class at FDA, Jernigan - Fort Deposit native, former civilian engineer for the Air Force, NASA engineer and Patriot Missile engineer - has been putting his years of hands-on technical knowledge and expertise to use this school year with his own "Fort Dale Physicists" - Larry Newton, Mason Bass, Chuck Barrett, Conyers Poole,

Edward Poole, Anna Kate Davis, Tammy Jo Bozeman, Taylor Hamilton, Dock Chastain, John Allen Bates, Carson Moseley, Elizabeth Cauthen, David Paulk, Gregg Faulkner, Courtney Giddens and Christopher Slagley.

&uot;Like most high schools, the students are somewhat limited by our school budget, so they must use their wits and their knowledge of fundamental physical principles to effect a measurement. You would be amazed at how accurate their measurements can be using simple, commonly available materials,&uot; says Jernigan.

Jernigan’s physics students have recently done experiments to determine the gravitational constant at the school; successfully measured the speed of sound in the Camellia City and created pyrotechnic rockets they are all eager to test fire (when the weather is just right).

A weighty issue

In case it's been a while since your own high school physics class, here's a brief refresher for you: the concept of gravitational constant comes to us from Sir Isaac Newton's Law of Gravitation.

The famed English mathematician (the one who supposedly had an "a-ha" moment concerning gravity after an apple fell upon his head while he was sitting beneath a tree) is the fellow who first quantified the behavior of the force of gravity (the force that exists among all material objects in the universe).

The earth’s gravitational constant, g, is a major factor in the weight that you read when you step on the bathroom scales. Here on earth, the gravitational constant is taken as about 9.81 meters per second, which is actually an average value, as measured in Greenwich, England.

The local value varies from place to place and is governed by several factors, including height above sea level.

Your weight is in direct proportion to the earth’s gravitational pull.

&uot;For example, if you weigh 180 pounds here on earth, on the moon – with a gravitational pull 1/6th that of earth’s – you would weigh a mere 30 pounds!&uot; explains Jernigan.

&uot;The value of g also affects our measurement of time. the common pendulum clock’s rate is inversely proportional to the square root of g…so clocks on the moon would run slower than here on earth!&uot;

Tick tock, tick tock

To measure the gravitational constant at FDA, Jernigan's students used the well-known pendulum principle, "the same one that keeps your grandfather clock running on time," explains the instructor.

"You see, the period of the pendulum - the time it takes to make one complete cycle - is proportional to the length of the pendulum and the earth's gravitational constant at the place it is being measuredŠin this case the Fort Dale campus."

If you are imagining such an experiment would require a great deal of elaborate equipment, such was not the case.

The students devised an experiment using a laboratory stand, a weight of known mass, and a one-meter length of knitting wool -" red knitting wool borrowed from fellow science teacher Ms. Davis's room just across the hall," laughs Jernigan.

Meticulous measuring

Make no mistake – the experiment was no walk in the park for the budding scientists. "A lot of effort was expended getting the length of the pendulum just right," stresses Jernigan.

However, the students made several sets of measurements, meticulously timing each one, each with 20 periods - "enough to get an average reading that was as unbiased and as accurate as possible."

The measured values were then "plugged into" the equation, and a solution for the gravitational constant at FDA was calculated.

The results, Jernigan says, were "astonishing."

"In spite of the fact of the simplicity of the setup, they came amazingly close to the currently accepted value of 9.81 meters per square second. The measured error was 0.029 percent - that's the equivalent of measuring the distance from Greenville to Fort Deposit to an accuracy of .0035 miles, just a few feet!" exclaims the physics instructor.

Faster than the speed…

The Fort Dale Physicists have also just completed an experiment determining the speed of sound at their school. The students successfully measured the speed of sound in Greenville, clocking it at 322.68 meters/sec., based on raw data.

&uot;The measurement was made using the property of resonance. We’ve all experienced the phenomena of resonance when we blow across the top of a Coke bottle, for instance. The tone varies depending on how deep the bottle is.

Add water, and the note increases,&uot; explains Jernigan. Jernigan’s

budding physicists used a calibrated tuning fork, and prepared a resonance apparatus with a very long test tube borrowed from the chemistry lab. By rigging up a setup so the level of water could be varied in the test tube, they could vary the level until resonance was observed.

The measurement of the length of the air column could then be used to measure the amount of time it took sound to travel the length of the tube.

While data reduction is still under way, and corrections have to be made for the diameter of the resonance tube, Jernigan says it can already be stated the measured accuracy is on the order of less than six percent – &uot;not too shabby, considering the simplicity of the setup and the lack of sophisticated instrumentation.&uot;

Rocket men… and women

A project much anticipated by Jernigan's students is the Annual Rocket Firing. "We feature pyrotechnic rockets each student designed, built and decorated. The rockets are all ready and the kids are excitedŠwe are just waiting for the right window of opportunity for the launch - a clear day with no wind," explains Jernigan.

The physics teacher is excited to be able to use simple objects to teach scientific principles to his budding physicists.

&uot;I think it really helps the kids understand the fundamentals so much better. Constants like the speed of sound and the earth’s gravitational constant are used every day in the physicist’s world, and they have a bearing on our everyday lives.&uot;

As for the students, many of whom are planning to enter science-related career fields, they feel having their own &uot;rocket scientist&uot; as a teacher is a real advantage.

&uot;Yeah, I definitely would say having Mr. Jernigan as a teacher is a plus for us,&uot; remarks Chris Slagley.