## Fourth Class Notes on Work, Heat and Energy (Principles of Heat and Fluids)

# 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

The product of the displacement (distance traveled) of the body multiplied by the component of the force in the direction of the displacement.

Imperial | SI Unit | |

W = Work | ft-lbf | N-m or Joule |

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

d = Distance traveled | ft | m |

**Example 1.** Find the amount of Work being applied when a weight of 1000 lb is lifted through a distance of 124 inches and express it in imperial unit standard as ft-lbf.

W = F x d

W = 1000 x (124 in x (1ft/12in))

W = 1000 x 10.33

W = 10330 ft-lbf

**Example 2.** A ventilating 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. Express the work in SI unit.

W =F x d = m x g x d

W = (165 kg) x (9.8 m/s^2) x (96 m)

W = 155,343 J

# 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) |

T = Time | sec | sec |

The horsepower (hp) is a widely used unit in the Imperial system

1 hp = 550 ft-lbf /sec = 746 watts

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

*In Imperial*

*In Horsepower*

*In Kilowatts*