P=nkT 3/2 f(v)= 1 dN 二4T m my2 N dv 2πkT v"exp 2kgT 1/2 m my2 n dv 2πkgT exp( ) 3/2 2 1 2 4 exp 2 2 B B dN m mv f v N d k T k T         = = −         P = nkT ( ) 1/2 2 1 exp 2 2 x x x x B B dn m mv f n d k T k T        = = −        