1
general::
Phrase(s): tap someone or something on something
to make one or more light blows on some part of someone or something. • Someone tapped me on the shoulder, and I turned around to see who it was. • I tapped the drum on the top to find its pitch., Phrase(s): tap on something
to make one or more light blows on something. • Who is that tapping on my windowpane? • I wish you would stop tapping on the tabletop.
McGrawhill's American Idioms And Phrasal Verbs