As each wave--first a compression, then a rarefaction--encounters an object, it exerts a force--a push, then a pull--on the object.
(first a compression; encounters; an object) (it; exerts; a force; T:As each wave--first a compression, then a rarefaction--encounters an object)
first a compression it
encounters exerts
an object
a force T:As each wave--first a compression, then a rarefaction--encounters an object