Question on drag

1. Aug 10, 2006

finchie_88

If the force of drag is proportional to the velocity, then:
$$F_d = -kv$$
However, the units of k are very strange. Does this mean that the model is completely wrong?

2. Aug 10, 2006

ZapperZ

Staff Emeritus
What do you mean by "strange"? What did you expect the units of "k" supposed to be?

Note that just because something is a constant, doesn't mean it doesn't have any units, or that it must have only certain types of units.

Zz.

3. Aug 10, 2006

finchie_88

By strange, I mean kg/s. Which seems strange in the idea of projectiles or falling objects (in rocket motion it would make much more sense).

4. Aug 10, 2006

ZapperZ

Staff Emeritus
I still don't see why it is strange. Why does having the unit of kg/s for the constant seem strange? It is, after all, connecting a "force" (which has a mass dependence), to a velocity (which has a time rate of change dependence).

Sounds perfectly un-strange to me.

Zz.

5. Aug 10, 2006

Hootenanny

Staff Emeritus
Would you consider it strange if we quoted the value of a force as 5 kg.m.s-2?