Question

a book is sitting on a desk. what best describes the normal force acting on the book? the upward force the desk pushes on the book the upward force the book pulls on the earth the downward force the book pushes on the desk the downward force the earth pulls on the book

Explanation:

To determine the normal force on the book, we recall Newton's laws. The book exerts a downward force (weight) on the desk, so by Newton's third law, the desk exerts an equal and opposite upward force on the book—this is the normal force. Let's analyze each option:

• Option 1: "the upward force the desk pushes on the book" matches the definition of normal force (desk exerts upward force on book to balance its weight).
• Option 2: The book pulling on Earth is gravity's reaction, not normal force.
• Option 3: The book pushing down on the desk is the action force (not normal force on the book).
• Option 4: The Earth pulling on the book is gravity (weight), not normal force.

Answer:

A. the upward force the desk pushes on the book