Fourth Class Notes on Work, Heat and Energy (Principles of Heat and Fluids)
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)
The product of the displacement (distance traveled) of the body multiplied by the component of the force in the direction of the displacement.
|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 is the time rate at which work is done or work per unit time.
|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.