If the woodpecker drums upon a tree 4 times in one second, then the frequency is 4 Hz each drum must endure for one-fourth a second, so the period is 0.25 s. Each drum must endure for one-half a second, so the period is 0.5 s. If the woodpecker drums upon a tree 2 times in one second, then the frequency is 2 Hz. As an example of the distinction and the relatedness of frequency and period, consider a woodpecker that drums upon a tree at a periodic rate. Period refers to the time it takes something to happen. Frequency refers to how often something happens. The period for the minute hand on a clock is 3600 seconds (60 minutes) it takes the minute hand 3600 seconds to complete one cycle around the clock.įrequency and period are distinctly different, yet related, quantities. The period of a typical class at a high school might be 55 minutes every 55 minutes a class cycle begins (50 minutes for class and 5 minutes for passing time means that a class begins every 55 minutes). The period of orbit for the Earth around the Sun is approximately 365 days it takes 365 days for the Earth to complete a cycle. Period, being a time, is measured in units of time such as seconds, hours, days or years. The period of a wave is the time for a particle on a medium to make one complete vibrational cycle. When an event occurs repeatedly, then we say that the event is periodic and refer to the time for the event to repeat itself as the period. Period refers to the time that it takes to do something. The quantity frequency is often confused with the quantity period. And if a coil makes 8 vibrational cycles in 4 seconds, then the frequency is 2 Hz (8 cycles/4 s = 2 cycles/s). If a coil of slinky makes 3 vibrational cycles in one second, then the frequency is 3 Hz. If a coil of slinky makes 2 vibrational cycles in one second, then the frequency is 2 Hz. Another unit for frequency is the Hertz (abbreviated Hz) where 1 Hz is equivalent to 1 cycle/second. Given this definition, it is reasonable that the quantity frequency would have units of cycles/second, waves/second, vibrations/second, or something/second. For example, it is not uncommon to hear a question like "How frequently do you mow the lawn during the summer months?" Of course the question is an inquiry about how often the lawn is mowed and the answer is usually given in the form of "1 time per week." In mathematical terms, the frequency is the number of complete vibrational cycles of a medium per a given amount of time. Frequency is a part of our common, everyday language. The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. This rate of 2 cycles/second is referred to as the frequency of the wave. In fact, every coil of the slinky would vibrate at this rate of 2 cycles/second. The third coil, being attached to the second coil, would vibrate at a rate of 2 cycles/second. The second coil, being attached to the first coil, would vibrate at a rate of 2 cycles/second. The first coil, being attached to the hand, in turn would vibrate at a rate of 2 cycles/second. The rate of the hand's motion would be 2 cycles/second. Suppose that a hand holding the first coil of a slinky is moved back-and-forth two complete cycles in one second. But the act of continually vibrating the first coil with a back-and-forth motion in periodic fashion introduces a wave into the slinky. A single back-and-forth vibration of the first coil of a slinky introduces a pulse into the slinky. This vibration creates a disturbance that moves through the slinky and transports energy from the first coil to the last coil. In that lesson, it was mentioned that a wave is created in a slinky by the periodic and repeating vibration of the first coil of the slinky. The nature of a wave was discussed in Lesson 1 of this unit.
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