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.