When two undulatory movements of equal nature cross the same region in space, their waves are superposed, in other words there is interference. At times you have been totally conscious of this phenomenon when you have had difficulty hearing your favourite radio station because of interference from another station.

This is because of a phenomenon which is particular to waves. When particles collide they cause mutual diversion, only waves can cross each other and continue on their way as if nothing had happened.

The easiest case of interference we can study is that which is produced in a taut rope which is shaken at two different points. We will study this in the next visual.