"Units and Conversion Factors" is a comprehensive reference guide designed to support engineering calculations on the FE exam. It addresses the mathematical relationships between different systems of measurement, specifically the Metric system and the U.S. Customary System (USCS).

A detailed description of its contents includes the following key sections:

1. Distinguishing Mass from Force in USCS

The text places significant emphasis on resolving the ambiguity in the U.S. Customary System where both force and mass are referred to as "pounds."

• Definitions: It distinguishes between pound-mass (lbm) and pound-force (lbf). A pound-force is defined as the force required to accelerate one pound-mass at 32.174 ft/sec2.

• The Conversion Factor (gc​): To ensure unit consistency in equations involving both mass and force, the text introduces the conversion factor gc​, defined as 32.174 lbm⋅ft/(lbf⋅sec2).

• Applications: The use of gc​ is required for consistent units in fundamental engineering equations, including:

◦ Newton’s Second Law: F=ma/gc​.

◦ Kinetic Energy: KE=mv2/2gc​.

◦ Potential Energy: PE=mgh/gc​.

◦ Fluid Pressure: p=ρgh/gc​.

• Differentiation from Gravity: The text explicitly warns against confusing gc​ (a unit conversion factor) with g (the local acceleration of gravity), which has units of m/s2 or ft/sec2 and varies by location.

2. Significant Figures and Accuracy

This section establishes the rules for determining the precision of calculated results.

• Identification Rules: Non-zero digits are always significant, as are zeros located between significant digits. For numbers less than one, zeros to the right of the first non-zero digit are significant, while for numbers greater than one, all zeros in the decimal portion are significant.

• Operational Rules:

◦ Addition/Subtraction: The result is dictated by the number with the fewest significant digits after the decimal point.

◦ Multiplication/Division: The result is limited by the input number with the fewest total significant digits.

• Engineering Standard: The text notes that for general engineering problems, it is customary to report the final result with 3–4 significant digits.

3. Fundamental Constants

The document lists essential physical constants required for solving problems across various disciplines:

• Universal vs. Specific Gas Constant: It distinguishes between the universal gas constant (Rˉ) and the specific gas constant (R), which is obtained by dividing Rˉ by the gas's molecular weight.

• Physical Constants: Values are provided for the electron charge (e), Faraday constant (F), Newtonian gravitational constant (G), standard gravity (g), and the speed of light (c).

4. Unit Conversion Tables

The majority of the text consists of extensive tables for converting between Metric and USCS units.

• Metric Prefixes: A table lists prefixes ranging from atto (10−18) to exa (1018).

• Temperature: Formulas are provided for converting between Fahrenheit, Celsius, Kelvin, and Rankine.

• Common Conversions: The source details conversion factors for a wide variety of quantities, including:

◦ Power: Watts to horsepower (1 kW=1.341 hp) or Btu/hr.

◦ Pressure: Pascals to atmospheres (1 Pa=9.869×10−6 atm) or psi to inches of mercury.

◦ Energy: Joules to Btu (1 J=9.478×10−4 Btu) and foot-pounds.

◦ Volume: Liters to gallons and cubic feet.