A simple pendulum of length 50 cm vibrates with an amplitude of 4.0 cm. In three cycles, the pendulum bob moves: 48 cm, 8.0 cm, 32 cm, 16 cm. For a transverse wave, one wavelength can be measured: from one crest to the next, from one trough to the next, from the beginning of one crest to the end of the adjacent trough, all of the above. As the frequency of a source decreases, the wavelength of a periodic transverse wave decreases, but the speed of the wave remains constant. When a crest travelling in one direction on a rope meets a crest travelling in the opposite direction, the result is destructive interference, constructive interference, a loop, a standing wave.
Amplitude (A): The maximum displacement of a pendulum on either side from its mean position in the horizontal direction is called amplitude.