In Physics (Thermodynamics), heat is not a substance; it is a form of energy transferred between two objects because of a temperature difference. Because heat is simply a form of energy, it shares its units with Work and Energy.
The British Thermal Unit (BTU) is another ancient unit of heat still used globally to measure the cooling power of Air Conditioners! (1 BTU is roughly 1055 Joules).
The official International System (SI) unit of heat is the Joule (J).
It is named after the brilliant English physicist James Prescott Joule, who proved that mechanical work can be directly converted into heat energy.
Before the Joule became the standard, scientists measured heat using the Calorie (cal). This is still heavily used today, especially in chemistry and biology (nutrition).
(Note: The 'Calories' you read on food packets are actually Kilocalories (kcal), which equal 1,000 standard calories).
You must know how to convert between the two units for physics problems: 1 Calorie = 4.184 Joules
(For most high school calculation problems, this is rounded to 4.2 Joules).
No! Heat is the *total* energy of all molecular motion inside an object (measured in Joules). Temperature is a measure of the *average* speed of those molecules (measured in Celsius or Kelvin).
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