Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: A force is a push or a pull on an object. When you place a book on a table, the book pushes downward on the table and the table pushes upward on the book. The two forces are equal and there is no resulting motion of the book. If, on the other hand, you hold the book in the air and let go, the force of gravity will pull the book to the ground. Answer: force
Output:
What is the term for a push or a pull on an object?