explain stationary waves?

Stationary or standing waves are formed in a medium when two waves having equal amplitude and frequency moving in opposite directions along the same line, interfere in a confined space. Generally, such waves are formed by the superposition of a forward wave and the reflected wave. Both longitudinal and transverse types of waves can form a stationary wave. When reflection occurs at a free end, there is no reversal of phase. i.e., a crest returns as a crest and a trough as a trough. Example, 1) A rope held vertically in the hand with the lower end hanging free, made to vibrate briskly at the upper end 2) An open end of an organ pipe into which air is blown When reflection occurs at a fixed end, there is a reversal of phase but there is no change in amplitude, frequency and velocity. i.e., a crest returns as a trough and a trough as a crest. Example, 1) A guitar string plucked in the middle. 2) A closed end of an organ pipe, into which air is blown. read less

"A standing wave – also known as a stationary wave – is a wave that remains in a constant position. Two opposing waves combine to form a standing wave. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions. In the second case, for waves of equal amplitude traveling in opposing directions, there is on average no net propagation of energy." (source:wiki) read less

When the wave, the vibrations to be specific, is in y- direction only, and not moving in x- direction. The nodes don't move, by definition, and only wave( the sine curve) moves up and down with no horizontal movement of the whole wave. See lecture 26 by Prof. Walter lewin, electricity and magnetism, MIT open course ware. Good luck. read less

This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions. In the second case, for waves of equal amplitude traveling in opposing directions, there is on average no net propagation of energy. read less