Si Units Engineering

Overview

Engineering reference data for Si Units Engineering in basics.

Key Formulas

Ohm's Law

$V = IR$

Voltage = Current × Resistance.

Newton's Second Law

$F = ma$

Force = mass × acceleration.

Conservation of Energy

$E_{in} = E_{out} + \Delta E_{stored}$

Energy balance.

Variables

SI Base Units

The International System of Units (SI) is built upon seven base units from which all other units are derived.

SI Prefixes

Decimal prefixes indicate multiples and submultiples of SI units.

Common SI Derived Units

Derived units are formed by combining base units according to algebraic relationships.

Dimensional Analysis

Dimensional analysis is a mathematical technique used to convert between unit systems and verify equations. The principle states that physical equations must be dimensionally homogeneous.

Dimensional Homogeneity

For any valid physical equation, each term must have the same dimensions:

$[\text{Force}] = [\text{Mass}] \times [\text{Acceleration}] = M \cdot L \cdot T^{-2}$

Common Engineering Dimensions

Unit Conversion Method

To convert a quantity $Q$ from one unit system to another, multiply by the appropriate conversion factor $C$:

$Q_{\text{target}} = Q_{\text{source}} \times C$

Example: Converting 100 km/h to m/s:

$100 \, \frac{\text{km}}{\text{h}} \times \frac{1000 \, \text{m}}{1 \, \text{km}} \times \frac{1 \, \text{h}}{3600 \, \text{s}} = 27.78 \, \frac{\text{m}}{\text{s}}$

Mass vs. Weight

Mass ($m$) is a measure of the amount of matter in an object and is constant regardless of location. Weight ($W$) is the gravitational force acting on a mass and varies with gravitational acceleration $g$:

$W = m \cdot g$

where $g \approx 9.80665 \, \text{m/s}^2$ at standard conditions (sea level, 45° latitude).

Interactive Charts

References

• Original Source