A book rests on a table. What is the Newton's third law pair of the normal reaction of the table on the book?
Answer and explanation
Correct answer: A. The force of the book pushing down on the table
- Step 1: Third-law pairs act on different bodies, are equal in size, opposite in direction and are the same type of force. Step 2. The table pushes up on the book (contact force), so the pair is the book pushing down on the table. Answer: The force of the book pushing down on the table. Why not the others: the weight is a gravitational force on the same body, so it only balances the reaction by Newton's first law; the resultant is not a single interaction force; the table-leg force involves a different pair of bodies.
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