4 root-mean- square speed(方均根速率) 1-2U m02==kT v=3kT/m 3kT 3kT4 root-mean-square speed （方均根速率） 3kT / m 2 m k T v = 2 3 2 1 2 v =  k T m 2 3k T 3 vrms = v = =