The Concept of Energy
Energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object. It is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed.
Introduction & History
The concept of energy emerged in the 19th century from the study of thermodynamics. Scientists like James Prescott Joule demonstrated the relationship between heat and mechanical work, leading to the formulation of the first law of thermodynamics. The unit of energy, the Joule, is named in his honor.
Key Units
Joule (J)
The SI unit of energy.
Kilojoule (kJ)
Equal to 1,000 joules, used in chemistry and nutrition.
Calorie (cal)
A unit of energy often used in the context of food, equal to about 4.184 joules.
Kilowatt-hour (kWh)
A unit of energy equal to the energy consumed by a one-kilowatt device in one hour, common on electricity bills.
Practical Applications
Physics and Chemistry
Nutrition and Dietetics
Electricity Generation
Thermodynamics and Engineering