Showed that mechanical work and heat are equivalent, establishing the mechanical equivalent of heat.
Practise Thermodynamics & Energetics All Thermodynamics & Energetics topics
James Prescott Joule carried out a series of experiments in the 1840s in which falling weights turned a paddle immersed in water, heating the liquid. He measured the mechanical work input and the resulting temperature rise, finding that about 4.18 joules of work raises 1 gram of water by 1 degree Celsius. This established the mechanical equivalent of heat, showing that heat is a form of energy rather than a separate indestructible fluid called caloric. The result was foundational for the first law of thermodynamics and the principle of energy conservation. The SI unit of energy, the joule, is named in his honor.
Key ideas: Joule measured the temperature rise of water stirred by falling weights, found about 4.18 J per gram kelvin, and showed that heat and work are interchangeable. Careful insulation, accurate thermometry and elimination of sound and friction losses were his achievements.
Common mistakes and connections: Do not think the experiment invented the first law outright, since several scientists contributed, including Mayer and Helmholtz. The caloric theory failed because heat could be created by friction without limit. It underpins the energy concept and the unit of the joule.
Paddle work converts to heat: temperature rises in proportion to the work done, giving the mechanical equivalent of heat of 4.184 J per calorie. The interactive lesson shows this as a live animation or chart.
Putting 4.18 J of paddle work into 1 g of water raises its temperature by about 1 degree Celsius, illustrating the equivalence of work and heat.
Showed that mechanical work and heat are equivalent, establishing the mechanical equivalent of heat.
Joule Experiment is a advanced topic in Thermodynamics & Energetics. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Thermodynamics & Energetics first: Entropy and the Arrow of Time, Heat Death Concept, Exergy.
The next topics in Thermodynamics & Energetics are Standard Conditions and Calorie vs Joule.
Yes. The interactive lesson includes a self-check question on Joule Experiment, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Joule Experiment is topic 82 of 91 in Thermodynamics & Energetics.