## Energy

Energy is the capacity or the ability to do work. It can be categorized into two forms:

Transient Energy (Mechanical Work, Heat)

Stored Energy (Kinetic, Potential)

### Mechanical Work

Imperial | SI | |

W = Work | ft-lbf | N-m or Joule (J) |

F = Force Applied | lbf | Newton (N) |

d = Distance travelled | ft | m |

Ex 1. Find the Work done when a weight of 1000 lb is moved through a distance of 124 inches.

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Ex. 2 A ventilation fan having a mass of 165 Kg is hoisted 96m from the ground to the roof of a building. Neglecting friction and other losses, compute the work done.

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### Power

Power is the time rate at which work is done or work per unit time.

Imperial | SI | |

P = Power | ft-lbf /sec | Watt (J-sec) |

W = Work | ft-lbf | N-m or Joule (J) |

Time | sec | sec |

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Ex 1. Determine the power required in kilowatts and horsepower to move an elevator weighting 2000 lbf vertically through 40 ft in 10 sec.

P = W/T = (F x d) / T = (2000 x 40) / 10 = 8000 ft-lbf /sec

P = 8000 ft-lbf /sec

P = 14.5 hp

### Heat

Heat is an energy in transition between two objects or substances due to their temperature difference. Heat always flows from a substance with a higher temperature to a substance with a lower temperature, regardless of sizes.

Heat Measurement:

**The British thermal unit (BTU):** The amount of heat required to raise the temperature of 1 lb of water by 1 Fahrenheit degrees

**The Calorie (Cal):** The amount of heat required to raise the temperature of 1 gram of water by 1 Celsius degrees.

Types of Heat

**Specific heat:**is the amount of heat required to raise the temperature of 1 lb. of a material by 1F

Specific Heat | Specific Heat | ||||

Substance | BTU/lb F | KJ/kg C | Substance | BTU/lb F | KJ/kg C |

Ice | 0.487 | 2.00 | Mercury | 0.033 | 0.134 |

Water | 1.000 | 4.19 | Aluminum | 0.214 | 0.902 |

Steam | 0.445 | 1.186 | Brass | 0.091 | 0.382 |

Wood | 0.327 | 1.37 | Copper | 0.092 | 0.385 |

Alcohol | 0.615 | 2.395 | Glass | 0.18 | 0.750 |

Machine Oil | 0.400 | 1.675 | Lead | 0.031 | 0.129 |

Fuel Oil | 0.564 | 2.362 | Cast iron | 0.120 | 0.420 |

Mild steel | 0.116 | 0.485 | Air | 0.24 | 1.007 |

**Sensible heat:**causes a change in the temperature of a material without causing a change of state.

**Latent heat:**not felt or sensed. It will not cause a thermometer to register a temperature change. However, it will cause a change of state of a substance. It is the amount of heat required to change liquid to gas or solid to liquid or vice versa.

Change of State | Terminology | Btu/lb | KJ/kg |

Ice to water | Melting | 144 Btu/lb | 335 KJ/kg |

Water to ice | Fusion | -144 Btu/lb | -335 KJ/kg |

Water to steam | Vaporization | 970 Btu/lb | 2257 KJ/kg |

Steam to water | Condensation | -970 Btu/lb | -2257 KJ/kg |

- Total heat: is the sum of the sensible heat and the latent heat.