# B Question about phase change

1. Sep 25, 2016

### Clara Chung

Why wont water wave undergo a phase change of pi when it propagates to a fixed wall just like a pulse of string does.

2. Sep 25, 2016

### drvrm

the change of phase of a wave takes place in a variety of circumstances upon hitting a reflecting wall.
it depends on how the wall reacts to the incident 'momentum transfer'.

a string tied at a fixed point -the waves on the string when hits the tied end it gets pushed by the incoming force and the reaction at the end is equal and opposite direction so a crest returns as a trough and there is a 180 degree change of phase .

sound waves which are waves of compression hitting a wall gets reflected without any change of phase.

water waves which are transverse waves in the medium transfers energy but the particle motion is perpendicular to the direction of propagation and when it gets reflected the reaction of the wall sends back a crest as a crest and a trough as a trough -
that is without any change of phase;
at the interface of wall and liquid layer the displacement as such is pushed back without changing its state of motion ,
whereas in the waves on the string if the last element is going up- it pulls on the fixed end and the reaction force acts in opposite direction -that it gets pulled down and leads to change of state of motion.