Lecture 19 - Shock Waves

Question 1

What are the two ways of obtaining shock waves?

Answer 1

1. Steepening of finite-amplitude sound waves

2. Supersonic compressive pertubations

Question 2

Are shock waves in the ISM ubiquitous?

Answer 2

Yes, they are

Question 3

Is Coulomb scattering fast?

Answer 3

No, an electron must scatter about m_ion/m_e times before approaching T_ion

Question 4

What is the general criteria for a shock?

Answer 4

It is:
• a pressure driven compressive disturbance
• propagating faster than the “signal speed” for compressive waves
• producing irreversible change in fluid state (increase of entropy)