|MadSci Network: Physics|
The metronome, as you know, is a device that is used to keep time for musicians. Thus it would stand to reason that the metronome would have to keep regular time, much like a watch. The difference is , however, that a metronome can be set to the desired beat, or count. This is accomplished by decreasing the length between the pivot or attachment point and the weight. This action makes the metronome swing from side to side faster, and increasing the length between the pivot and the weight will make the arm swing slower. The time it takes for the pendulum, ( think of a metronome as a pendulum upside down) to swing from one side to the other and back again is called the period. The movement of the pendulum, any pendulum, is called simple harmonic motion. As the metronome (pendulum) swings one way, a magnet (or a wound up spring) pulls on the metallic bar and causes it to accelerate toward the zero point or center. At this point the acceleration is zero, and the velocity is at the maximum. As the bar continues to move in that same direction the magnet causes a deceleration at the moment the bar passes the center. This force continues until the bar reaches a velocity of zero. This would be the point at which the metronome has reached the maximum distance away from the center on the opposite side from where we began. This action continues as long as the machine operates. Because the action is precise and regular, pendulums are used to keep time in clocks, as well. Quartz crystals vibrate at a particular frequency which can be considered simple harmonic motion, and are very useful in watches. Mathematical formulas can be obtained from any physics text. Simple experiment. Tie a weight on the end of a string that is exactly 20cm long. (20cm from the center of the weight to the point of attachment.) Pull the pedulum 10 cm away from the center and time the period. (Remember, the period is the time from one side to the other and back again.) Do this again except with a 10cm length of string. See what happens. ( Keep time even as the pendulum slows down!) Thanks for the question, Robert L. Judge Holy Cross School, New Orleans
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