The amazing normal forces

TL;DR

This paper aims to improve students' understanding of normal and friction forces in physics by using informal explanations and everyday experiences, emphasizing the deformation of objects and the action-reaction principle.

Contribution

It introduces an intuitive teaching approach that links real-world experience with fundamental physics principles to clarify the normal and friction forces relationship.

Findings

Normal forces are related to object deformation.

Friction forces follow from the action-reaction principle.

Traditional formulas are explained through physical observations.

Abstract

This manuscript is written for students in introductory physics classes to address some of the common difficulties and misconceptions of the normal force, especially the relationship between normal and friction forces. Accordingly, it is intentionally informal and conversational in tone to teach students how to build an intuition to complement mathematical formalism. This is accomplished by beginning with common and everyday experience and then guiding students toward two realizations: (i) That real objects are deformable even when deformations are not easily visible, and (ii) that the relation between friction and normal forces follows from the action-reaction principle. The traditional formulae under static and kinetic conditions are then analyzed to show that peculiarity of the normal-friction relationship follows readily from observations and knowledge of physics principles.