The third mode in a bathtub has a wavelength of 1.2 m. The difference between the string and the waver is that the string is tied down at the end while the water is left free to vibrate. This turns out to be an important difference. It's also possible to have situations where one end of the medium is restricted while the other is free to move. A string, 1.8 m long, is held at one end and free to vibrate at the other.
Sound waves differ from waves in a string in a fundamental way.
While the string wave travels horizontally along the string, the individual particles of the string move vertically at right angles to the direction of wave travel. This is not the case with sound. While a sound wave travels horizontally, the motion of the air molecules is also horizontal. Here are two names you should know. The wave in which particle motion is perpendicular to wave direction is known as a transverse wave.