The Foucault Pendulum.........
Pendulums.....Dissected!
Finally!LESSON REVIEW # 2B October 24, 2000
Cleophas Mike McAlpin......Tutor
Marci Williams.............Tutor
The Foucault Pendulum.........
Pendulums.....Dissected!
Finally!
Keyotta had an extra-credit report to do for her Physics class. I picked up Keyotta from Long Beach Polytechnic High School and Jarrell from Banning High School and brought them over to Dominguez Hills. I assisted Keyotta with the report and the other students with homework. I introduced the project to all of the students in attendance and included a lesson in Algebra. Other students in attendance were Asia, Sheena, Cleasena, Michael, James and Jeremiah.
Jarrell started on his Biology homework from Banning High School, while Keyotta and I researched the... "Foucault pendulum".
Keyotta's report appears below. The report calculates the acceleration due to gravity, "G", by using the simple pendulum.
|
By Keyotta Delemenea October 25, 2000
I visited the Griffith Park Observatory on March 26, 2000. I saw a most fascinating sight in the lobby. There was a giant steel ball of perhaps 30 pounds attached to thin wire of perhaps 50 feet. The thin wire was attached to the ceiling of the Observatory. The steel ball was swinging to and fro.
As the ball swung from one side to the other, an object
that was attached to its bottom contacted a row of rubber fingers (or what
appeared as so). The object knocked over a finger when the pendulum passed
across the row. Then it knocked over other finger on its next passes. I, along
with many other visitors, leaned against a railing and watched as the pendulum
continued swinging and the fingers continued falling.
I was so fascinated that I researched the device and
found it to be a Foucault pendulum. It was in
1851 that Leon Foucault devised an experiment with
a pendulum that demonstrated the rotation of the Earth. Many such pendulums hang
in Museums and Observatories around the world.
A simple pendulum is a device that has a weight attached
to one end of a string. While the other end of the string is attached to a fixed
point, the weight is allowed to swing to and fro. Such a device is undergoes
“simple harmonic motion” and it is my intention to describe that motion in
this document. There are certain terms that I will define and a certain formula
that I will use to duplicate Foucault’s experiment of the mid 1800’s.
The first thing that I did was to obtain a string of
exactly 3.28 feet. That is a metric length of 0.305 x 3.28= 1.000 meters. It was
amazing to me to find out that the weight attached to the string could be any
amount, as long as it is not so light as to be seriously affected by air
friction. I next attached the one end of the string to a metal ball of
approximately ½ of a pound and fixed the other end of the string to the
ceiling. I raised the ball so as to make an angle of 20°
- 30°
to the vertical (see diagram # 1, below) and dropped the ball. It swung to and
fro just as the Foucault pendulum had done at the Observatory.
I took out a stopwatch and timed the oscillations of the
pendulum. One oscillation occurred when the pendulum moved from the top of its
left swing, over to the other side and back to the top of its left swing. This
is what is known as the Period of the
oscillation and is given the letter “T” in
most scientific books. I took 10 measurements
with my stopwatch and got the average time it
took for one oscillation. That time was 2.0
seconds.
During my research, I found a formula that described the
workings of my experiment. It said that the Period, T,
is equal to 2 p
times the square root of the length of the string divided by the acceleration
due to gravity. The acceleration due to gravity, G,
is equal to 32.2 feet/second2 or
9.8
meters/second2
It occurred to me that if my experiment were correct, I
could find out the acceleration due to gravity as a check. After all, I had a
formula that contained three unknowns and I knew two of them. One was the length
of the string and the second was the Period or
time for one oscillation. It my experiment were correct, then the
acceleration, G, would figure to be
32.2
feet/sec2 or 9.8 meter/sec.2
See diagram # 2, below for my calculations.
In conclusion, I will say that a pendulum can be used to keep accurate time. It is for this reason that many clocks contain pendulums.
There is a sort of pendulum on my science teacher’s (
Ms. Struett) desk. A steel ball is
attached to wire and the ball would swing from one side to the other, except
that its energy is transferred to a series of other balls that are suspended by
strings and in the same plane. The other balls transfer the energy to an end
ball that continues the swing of the first, in a way. I watch that device with
the same interest that I had for the Foucault
pendulum at the Griffith Park Observatory.
Formula:
T= 2p
Ö
L/G
To find G:
T2 = (2pÖ
L/G) 2
T2 = (2p)2
L/G
G= (2p)2
L ¸
T2
G= (39.48)(3.28)
¸
4
G= 32.37 ft/sec2
