For each of the following interactions, identify the action and reaction forces: (a.) A hammer hits a nail. (b.) Earth's gravity pulls down on a book. (c.) A helicopter blade pushes air downward.

A hammer hits a nail, is an example of action force

The earth gravity pulls down on a book is a reaction force because before earth gravity can be active, there must be an action first, maybe the book tossed in the air.

Helicopter blade pushes air downward is a reaction as the helicopter is reacting to the force inert on it by air