18 Pa.C.S.A. §301.  Requirement of voluntary act.

(a)  General rule.–A person is not guilty of an offense unless his liability is based on conduct which includes a voluntary act or the omission to perform an act of which he is physically capable.

(b)  Omission as basis of liability.–Liability for the commission of an offense may not be based on an omission unaccompanied by action unless:

(1)  the omission is expressly made sufficient by the law defining the offense; or

(2)  a duty to perform the omitted act is otherwise imposed by law.

(c)  Possession as an act.–Possession is an act, within the meaning of this section, if the possessor knowingly procured or received the thing possessed or was aware of his control thereof for a sufficient period to have been able to terminate his possession.