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
