The units of b are newton seconds per meter . Great Truths . Not all dampers obey it. This is a Great Truth. And it's always true, not just approximately but exactly.
Velocity is the time-derivative of displacement.
This is always true, but it's not very deep. It's a Truth, but it doesn't aspire to Greatness. Some dampers behave in a way that can be described pretty well by this equation, and some don't. For a damper, this graph will have axes f and v . I like to think of a graph as having an input variable and an output variable.