Creating A Pendulum
The working mechanism should look like this
Driving Question: Why was the pendulum used for such important things as time keeping and detecting earthquakes?
~Materials~
The Pendulum stand (three pieces)
First of all, I would like to say that my project's kit did not come with a procedure, so most of this is trial and error. Thank you.
~Procedure~
1. Thread the nylon strings through the metal balls.
Nine pieces of nylon string of approximately two feet in length
2. Run the ends of the thread through the holes in the "back" of the pendulum brace and then run one of the brass cinches over the ends sticking out of the holes. Tie a swift knot, leaving enough string for the ball at the end to float just above your hand on a flat surface.
Nine metal balls with wholes bored through the center.
1
And twenty two little brass cinches.
2
3
4
Do this with all of the balls and strings. Go carefully, as this can be tedious work. *If you're in a hurry and want to string all the balls up at once, use tape to hold the strings in the optimal position.*
The finished product should look something like this:
As I said, the strings were all the same length, so it makes sense that there would be extra left over. I assume you would be instructed to cut it of if you received a construction manual, but, as I said at the top of the page, I did not get one, and I personally decided to keep the extras just in case this project is reused in later PBL projects.
~Science Involved~
The period of a simple gravity pendulum is independent of the mass of the bob. If the amplitude is limited to small swings, the period ( T ) of a simple pendulum is:
where L is the length of the pendulum and g is the local acceleration of gravity.
When a pendulum is displaced, the force of gravity makes it move downward, but as it swings it is unable to stop at its equilibrium, and will move in the opposite direction until gravity pulls it back again. By measuring the oscillation of the pendulum, it's possible to measure the gravitational force or acceleration of the pendulum.
In a resonant system (A), the pendulums hang from a common rod and are simultaneously excited by a short twist to the rod. In a travelling wave (B), the excitation is applied to the shortest pendulum and the energy moves progressively to neighbouring longer ones through rubber bands which supply coupling. In both cases a wave-like motion of the pendulums is seen. (1)
Glossary:
Damping: a decrease in the amplitude of an oscillation as a result of energy being drained from the system to overcome frictional or other resistive forces.
Period: The period of a wave is the time for a particle on a medium to make one complete vibrational cycle.
Frequency: The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium.
Bob: A bob is the weight on the end of a pendulum most commonly, but not exclusively, found in pendulum clocks.
Resonance: the condition in which an object or system is subjected to an oscillating force having a frequency close to its own natural frequency.
Reference: