( They ( ( ( ( collide ( ( ( with ( each other ) ) and ) ( also ( with ( ( ( both ( ( neutral and ) ionized ) ) atoms ) ( of gas ) ) ) ) ) ) , ) ( so ( that ( ( dust particles ) ( are ( ( ( subjected ( to ( hydrodynamic ( and ( magnetic forces ) ) ) ) ) ( in addition ) ) ( to gravity ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP collide) (PP (PP (IN with) (NP (DT each) (JJ other))) (CC and) (PP (ADVP (RB also)) (IN with) (NP (NP (ADJP (DT both) (JJ neutral) (CC and) (JJ ionized)) (NNS atoms)) (PP (IN of) (NP (NN gas)))))) (, ,) (SBAR (RB so) (IN that) (S (NP (NN dust) (NNS particles)) (VP (VBP are) (VP (VBN subjected) (PP (TO to) (NP (JJ hydrodynamic) (CC and) (JJ magnetic) (NNS forces))) (PP (IN in) (NP (NN addition))) (PP (TO to) (NP (NN gravity)))))))) (. .)))
They collide with each other and also with both neutral and ionized atoms of gas, so that dust particles are subjected to hydrodynamic and magnetic forces in addition to gravity.
(ROOT (S (NP (NNP Gravity) (CC and) (NNP magnetism)) (VP (VBP are) (NP (DT both) (JJ common) (NNS forces))) (. .)))
Gravity and magnetism are both common forces.