Energy is defined as the capacity of a body to do work. The energy around us exists in many different forms, however, the most important forms of energy are mechanical energy, electrical energy, and thermal energy. Mechanical energy is expressed as newton meters or joules, while electrical energy can be expressed as watt-sec or kilowatt-hour. Heat energy can be expressed as calories, B.Th.U or CHU.

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## Electrical Energy

Electrical Energy can be expressed using one of the below-mentioned units:

- watt-second
- joule
- watt-hour
- kilowatt-hour

One watt-second or joule energy is transferred between two points if a potential difference of 1 volt exists between them and 1-ampere current flows through them for 1 second.

Practically, the unit **kilowatt-hour** is used since watt-sec or joule are very small units of energy.

## Units of Mechanical Energy

Mechanical energy is expressed in newton-meter or joule on or SI system, where one newton-meter (or joule) is the work done on a body is if a force of one newton moves it through a distance of one meter.

Mathematically, joules = Force in Newton * Distance in meters

Heat Energy Units

## Calorie

1 Calories is the defined as the amount of heat energy required to raise the temperature of 1 gm of water through 1°C. Mathematically 1 calories = 1 gm of water * 1°C

Good to know: Several definitions of the calorie are now in common use, some of these include:

Thermochemical calorie | 1 cal = 4.184 | J (exact) |

15 °C calorie | 1 cal = 4.1858 | J |

International Table calorie | 1 cal = 4.1868 | J (exact) |

Mean calorie | 1 cal = 4.1900 | J |

## Centigrade Heat Unit (CHU)

The amount of heat required to raise the temperature of one pound of water by one Celsius degree.

Mathematically: 1 CHU = 1 lb * 1°C

## British thermal unit (B.Th.U)

The amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

Mathematically: 1 B.Th.U = 1 lb * 1°F