Lecture 1: Units and Dimensions

1.1 The International System of Units (SI)

Physics is an experimental science. Experiments require measurements, and measurements are usually recorded as numbers. Every number that expresses a physical quantity must be accompanied by a unit. The standard system used by scientists worldwide is the Système International (SI).

The three fundamental quantities in mechanics are:

• Length: The meter (m)
• Mass: The kilogram (kg)
• Time: The second (s)

1.2 Dimensional Analysis

Dimensional analysis is a powerful tool for checking the consistency of physical equations. Every physical quantity has dimensions associated with it, regardless of the units used to measure it. For example, speed has dimensions of [Length] / [Time].

We will use this throughout the course to verify our derivations and ensure that we are not adding "apples and oranges."