# Wave pulses on a string

1. Oct 31, 2013

### Jimmy87

Hi, please could someone explain why a wave pulse travelling down a rope inverts when it strikes a fixed boundary. Is it something to do with conservation of momentum?

2. Oct 31, 2013

3. Nov 1, 2013

### GregoryS

There are no any problems with conservation of momentum: if we consider a longitudinal wave, then a wave pulse will push a fixed boundary which pushes the Earth which changes slightly its orbit.

4. Nov 1, 2013

### Philip Wood

At least two ways of understanding it...

(1) Assume (though we don't have to) that the wave is transverse and in the vertical plane, and that the pulse is an upward 'kink' in the rope. When the start of the kink reaches the wall it exerts an upward force on the wall. So what is the direction of the force that the wall exerts on the string (initiating the reflected wave)?

(2) What is the RESULTANT displacement of the string at the wall due to the incident and reflected waves? What therefore must be the direction of the reflected wave at the wall?