velocity = frequency x wavelength
For transverse waves, the individual disturbance is perpendicular to the direction of the wave motion as a whole. A wave on a rope is a transverse wave.
For longitudinal waves, the individual disturbance is along the same direction as the wave motion as a whole. Sound is a longitudinal wave.
Waves can pass through each other and continue on; this is known as superposition.
If we wiggle the end of a string at the right frequency, the waves along the string reinforce the waves being reflected and a large-amplitude standing wave is produced. This is another example of resonance.
(C) 2003, Doug Davis; all rights reserved