3)方均根速率 f(0) N udw Nf(odu O 3kT 3RT 2 3kT rms VM kT RT 7≈1.60 =1.60 2 0<7<V0 2KT 2RT M3）方均根速率 2 v m 2 3kT v = M R T m 2 3kT 3 vrms = v = = v f (v) N o Nf N N N    = = 0 2 0 2 2 v d v (v)dv v 2 p v  v  v M R T m kT v 1.6 0 =1.6 0 M RT m 2kT 2 vp = =