On static equilibrium and balance puzzler

TL;DR

This paper clarifies the principles of static equilibrium, highlighting misconceptions about stability and equilibrium states, and explains that structures can be in equilibrium without being firm or steady.

Contribution

It provides a detailed analysis of static equilibrium principles, clarifies common confusions, and emphasizes that equilibrium does not necessarily imply stability or firmness.

Findings

Equal weights can be in equilibrium even if the beam is not horizontal

Neutral equilibrium is often mistaken for stable equilibrium

Structures in static equilibrium may not be firm or steady

Abstract

The principles of static equilibrium are of special interest to civil engineers. For a rigid body to be in static equilibrium the condition is that net force and net torque acting on the body should be zero. That clearly signifies that if equal weights are placed on either sides of a balance, the balance should be in equilibrium, even if its beam is not horizontal (we have considered the beam to be straight and have no thickness, an ideal case). Thus, although the weights are equal, they will appear different which is puzzling. This also shows that the concept of equilibrium is confusing, especially neutral equilibrium is confused to be stable equilibrium. The study not only throws more light on the concept of static equilibrium, but also clarifies that a structure need not be firm and steady even if it is in static equilibrium.