微元体所受的表面力 or(rp,)+agta(rp )]dededr l 06 (ro2)+=+on+-(ro0)le+ 06 ()+2n+2()E}mk 06 微元体所受的重力 FB=pgrord00z=(pg, e,+pgee+pge ror800z[ ( ) ( )] {[ ( ) ( )] [ ( ) ( )] [ ( ) ( )] } S r z r rr zr r r r z z rz zz z p F rp rp d dzdr r z r r e r z r r e r z r r e drd dz z z                              = + +       = + − + +       + + + +       + +    微元体所受的表面力 微元体所受的重力 ( ) F gr r z g e g e g e r r z B r r z z = = + +          