**Herong's Notes on Physics** - Version 3.21, by Dr. Herong Yang

Meter Prefixes and Other Units

This section introduces prefixes used on 'meter' to represent decadic multiples or fractions of a meter. It also covers other standard units to measure distances like foot, mile, nautical mile and lightyear.

For the convenience of measuring a very long or very short distance, some prefixes have been defined on "meter" to be decadic multiples or fractions of a meter. Here are some commonly used meter prefixes and their abbreviated symbols:

Prefix Name Symbol Definition peta petameter Pm 1 000 000 000 000 000 meters tera terameter Tm 1 000 000 000 000 meters giga gigameter Gm 1 000 000 000 meters mega megameter Mm 1 000 000 meters kilo kilometer km 1 000 meters meter m 1 meter deci decimeter dm 0.1 meter centi centimeter cm 0.01 meter milli millimeter mm 0.001 meter nano nanometer nm 0.000 000 001 meter pico picometer pm 0.000 000 000 001 meter femto femtometer fm 0.000 000 000 000 001 meter

Beside "meter", other standard units are also used to measure distances. For example:

- "foot" - "foot" was originally defined as the average foot (shoe include) length of Europeans. It is standardized now that 1 foot = 0.3048 meter.
- "yard" - "yard" is defined as 3 times of 1 foot. That means 1 yard = 0.9144 meter.
- "inch" - "inch" is defined as 1 12th of 1 foot. That means 1 inch = 0.0254 meter.
- "mile" - "mile" was originally defined as 1,000 paces, where each pace (about 5 feet) is the distance covered by two steps of a marching Roman soldier. It is standardized now that 1 mile = 1,609 meters.
- "nautical mile" - "nautical mile" was originally defined as one minute arc length along any meridian line. Since a meridian line has 360 degrees and each degree has 60 minutes, so the entire length of a meridian line is 21,600 (360*60) nautical miles, which is about 40,000,000 meters. Based on this, 1 nautical mile is about 1,852.85185 meters by the original definition. It is standardized now that 1 nautical mile = 1,852 meters.
- "lightyear (ly)" - "lightyear" is defined as the distance that light travels in vacuum in one year. We know the speed of light is 299,792,458 meter per second. So a lightyear is about 9,454,254,955,488,000 meters, clost to 10 petameters.

*Last update: 2014.*

Table of Contents

Meter Based on Earth's Meridian

Meter Based on Seconds Pendulum

►Meter Prefixes and Other Units

List of Various Distances and Lengths

Introducion of Frame of Reference

Introduction of Special Relativity

Time Dilation in Special Relativity

Length Contraction in Special Relativity

The Relativity of Simultaneity