---
title: "A block of mass \\(m\\) is at rest on a horizontal table. The Earth exerts a downward gravitational force of magnitude \\(mg\\) on the block, and the table exerts an upward normal force of magnitude \\(F_N\\) on the block. Which of the following correctly identifies an action-reaction pair of forces for this system according to Newton’s third law?"
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url: "https://nerd-notes.com/ubq/109255/"
date_modified: "2026-03-22T06:04:21+00:00"
---

# A block of mass \(m\) is at rest on a horizontal table. The Earth exerts a downward gravitational force of magnitude \(mg\) on the block, and the table exerts an upward normal force of magnitude \(F_N\) on the block. Which of the following correctly identifies an action-reaction pair of forces for this system according to Newton’s third law?

A block of mass \(m\) is at rest on a horizontal table. The Earth exerts a downward gravitational force of magnitude \(mg\) on the block, and the table exerts an upward normal force of magnitude \(F_N\) on the block. Which of the following correctly identifies an action-reaction pair of forces for this system according to Newton's third law?

![A rectangular block sits centered on a flat horizontal table surface. A small dot represents the center of mass of the block. An arrow labeled mg points downward from the center of mass. An arrow labeled F_N points upward from the surface of the table into the block.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1774119120-G808xK.jpg)

- **A.** The downward gravitational force from Earth on the block and the upward normal force from the table on the block are an action-reaction pair because they are equal in magnitude and opposite in direction.
- **B.** The upward normal force from the table on the block and the downward normal force from the block on the table are an action-reaction pair because they represent the mutual contact interaction between the two surfaces.
- **C.** The downward gravitational force from Earth on the block and the upward gravitational force from the table on the block are an action-reaction pair because the table is supporting the block's weight.
- **D.** There are no action-reaction pairs in this scenario because the block is in equilibrium and the net force on the block is zero.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/109255/*