megajoule

Megajoule (symbol MJ) is a unit of energy in the International System of Units (SI). It equals one million joules (10^6 J) and is used to express energy in mechanical, chemical, and electrical contexts. The megajoule sits between the kilojoule and the gigajoule on the energy scale.

Conversions and context: 1 MJ = 1,000 kJ. Since 1 kilowatt-hour equals 3.6 million joules, 1 MJ is about 0.2778 kWh. In practice, energy contents of fuels are often quoted in MJ per liter or per kilogram; gasoline is typically around 34 MJ per liter (LHV) and about 44 MJ per kilogram. In electricity, megajoules provide a convenient measure of energy transfer or storage in motors, turbines, and batteries.

History and usage: The prefix mega- denotes a factor of one million, and the joule is named after James Prescott Joule. The megajoule is an SI-derived unit and is widely used in science, industry, and energy policy to quantify large amounts of energy.