Continuity of velocity at the interface

[SDRK]

Dear experts,

While solving the wave transmission at an interface for an acoustic wave problem, a boundary condition states that the "velocity of a fluid particle at the surface must be continuous". Could you please let me know why is it required, and a physical insight of what would happen if the velocity was discontinuous at the interface.

Thanks,
Rahul

 

[Dr.D]

A velocity discontinuity at the interface would imply that a particle moving toward the interface would have a sudden change in momentum at the interface. Where is the necessary impulse going to come from? The required impulse is absent, therefore there can be no change in momentum at the interface

 

[SDRK]

Thanks Dr.D for your reply. Could you also give me an example (in practical) of a case where there would be a velocity discontinuity at the interface?

Thanks a lot!

 

[Dr.D]

After I just explain you why it cannot happen, you now ask for a practical example where it does happen. I give up.

 

[SDRK]

After I just explain you why it cannot happen, you now ask for a practical example where it does happen. I give up.

Oh, I clearly understood the concept you mentioned...However,I was just curious to know if there would be a case of an impulse at the interface to create discontinuity of velocity.