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Mechanical equivalent of heat
Intermediate
Joule showed work can be converted to heat at a fixed rate.
1 cal = 4.186 JJoule's paddle-wheel experiment showed a fixed amount of work yields a fixed amount of heat: 1 cal = 4.186 J. This established energy conservation including heat.
Falling 427 m raises water 1 K per kg.
Calories on food labels are kilocalories.
In more detail
Joule's experiments showed that mechanical work can produce the same heating effect as a known amount of heat. This established that heat is a form of energy and gave the mechanical equivalent of heat.
Real-world uses
- Historical experiments that led to the conservation of energy principle.
- Modern calorimetry uses the same idea to measure energy transfers.
- Joule's experiments with paddle wheels in water showed that mechanical work heats the liquid by a fixed amount.
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Frequently asked questions
What is the mechanical equivalent of heat?
About 4.18 joules for every calorie, the energy needed to warm a gram of water by one degree Celsius.
Who was Joule?
James Prescott Joule, whose experiments in the 1840s established the equivalence of work and heat.
Why is one calorie about 4.2 joules?
That is the energy needed to warm one gram of water by one degree, which Joule's work helped to establish.
Related topics in Work, Energy & Power
Rolling without slipping energy · Work done by gravity on incline · Heat as energy transfer · Mass–energy equivalence · Sources of energy · Renewable energy