✓ Sources checked · 10 September 2026 · View verification
Work is a transfer of energy through a force acting over displacement. For a constant force, W = Fd cos θ; motion alone or force alone does not guarantee nonzero work by that force.
By Matan · Updated
Energy, work and power
Energy and work are measured in joules. Power measures energy-transfer rate in watts, with 1 W = 1 J/s. Kinetic energy of a classical particle is ½mv². Gravitational potential-energy change near Earth is approximately mgΔh for a system including Earth. [1], [2]
Worked lift with balanced forces
Lift a 2 kg object slowly through 1.5 m at g = 9.8 m/s², without a net kinetic-energy change. The lifting force does +29.4 J of work, gravity does −29.4 J, and net work on the object is zero. Its gravitational potential energy in the Earth–object system increases by 29.4 J. These are compatible statements about different accounting choices.
A force can do zero work during motion
If a constant upward support force carries a bag horizontally at fixed height, its work is zero because it is perpendicular to displacement. Holding a bag still also gives zero mechanical work on the ideal stationary bag, even though muscles consume energy internally.
Do not double count
Use gravity’s work or a potential-energy change consistently in the chosen energy balance. Friction and deformation can convert mechanical energy into internal energy; total energy accounting requires including these transfers. The lift is an ideal quasistatic example.
Continue learning
- Work in Physics (Without Breaking a Sweat)
- Power: How Fast Work Gets Done
- The Law of Conservation of Energy
- Potential and Kinetic Energy Explained
How this article was checked
Sources checked; calculations checked where shown. The definitions, model assumptions and main explanatory claims were cross-checked against the sources below. Worked-example arithmetic and units were checked separately. These examples are illustrative calculations, not experimental measurements.
Source cross-check and editing assisted by AI. No independent human scientific review is recorded for this revision. The check applies to the version dated 10 September 2026; it is not a guarantee that every possible interpretation is correct.
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Sources and further reading
- OpenStax: Work and direction — Work and direction.
- OpenStax: Net work and kinetic energy — Net work and kinetic energy.
Cite this article
Matan. “Energy and Work.” Your Physicist. Originally published 2026-06-11; updated 2026-09-10. https://your-physicist.com/energy-and-work/
Revision history
: Replaced the force-plus-motion shortcut with the dot product and a checked lift energy balance. Added linked sources and a transparent verification record.
