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Imagine pushing against a solid concrete wall until your muscles ache and sweat drips down your face. In everyday life, you just worked hard β€” but in physics, you did strictly zero work.
How can an exhausting physical effort count as zero in the laws of nature?

What Is Work in Physics?

In physics, work is the transfer of energy that occurs when an applied force causes an object to move through a displacement.
In 1826, French engineer Gaspard-Gustave de Coriolis coined the term "work" to describe the practical task of lifting buckets of water and ore out of mine shafts using early steam engines.
Only the portion of the force pointing directly along the direction of motion actually transfers energy to the object.
Mathematically, work is defined as W=Fdcos⁑θW = F d \cos\theta, where FF is force magnitude, dd is displacement magnitude, and θ\theta is the angle between them.
Because force is measured in newtons (N\text{N}) and displacement in meters (m\text{m}), the standard unit of work is the joule (J\text{J}), where 1Β J=1Β Nβ‹…m1\text{ J} = 1\text{ N}\cdot\text{m}.
So under what exact circumstances does work actually equal zero?

The Three Conditions for Work

For work to be done on an object, three distinct physical conditions must be met at the same time.