Stationary (or standing) waves are the result of a collision between two waves of equal amplitude and frequency. They occur when a wave is confined and reflects between two boundaries.
Imagine you tied a rope to a wall and sent a pulse down the rope (Fig. 16.21). It would travel down, reflect off the wall and travel back. That would continue until the vibration dropped off. But if you continued to send pulses down the rope, each pulse would meet its reflected pulse coming back and interfere to form a stationary wave.
Stationary waves are also called standing waves because they appear to be standing in one place. In reality, all parts of the wave are vibrating at equal frequency but the amplitude may be anywhere from minimum to maximum, depending on which part of the wave you are looking at (Fig. 16.22).
Stationary waves are waves of the same frequency and amplitude that constructively and destructively interfere to produce a wave pattern in a confined space.
FIG. 16.21 Stationary waves are caused by the collision between two waves of equal amplitude and frequency
FIG. 16.22 Transverse standing waves can be seen in guitar strings
Standing waves can be set up with longitudinal or transverse waves. Fig. 16.23 shows the equipment needed to create a stationary longitudinal wave in a slinky spring. For stationary transverse waves, use the equipment shown in Fig. 16.24.
slinky spring signal generator signal generator string
vibration generator
FIG. 16.23 Creating a stationary longitudinal wave
