The Metric System

Variables |
| Question: What is a variable? |  |  |  |

| A variable is anything that can be measured. Scientific experiments are done by measuring these variables. There are thousands of variables and new ones are being created every day. |

| What is required when a new variable is created in order to begin to take measurements?
| A unit that allows everyone to agree on the size of the measurement for that variable.
Systems of Units
| Over the last several hundred years, a number of systems of variables and units have been developed. There are two main systems in use in the world today, the English system and the metric system (also known as the SI system).
| Question: Name the countries that do not officially use the metric or SI system.

| Each system has to start with a number of fundamental or basic variables for which a unit must be defined. The basic variables used in Mechanics are shown below for the Metric and the English systems.
| Metric System |  | English System |
| Variable | Unit |  | Variable | Unit |
| length | m |  | length | feet |
| time | s |  | time | s |
| mass | kg |  | mass | - |
| weight | - |  | weight | lb |

| It's universal, everyone uses it. It's based on powers of ten (orders of magnitude) - uses prefixes so there is only one unit - easy to convert from one prefix to another |

| Question: What are the missing units for metric weight and english mass?
| Metric unit for weight is the Newton. English unit for mass is the slug. |
United States, Burma(or Myanmar), & Liberia

| Question: What makes the metric system better so that almost every country in the world uses it?

| "If God had intended humans to use the metric system, they would have been given 10 fingers."
Defining Units
| In order to define a unit for a given variable, a standard that allows everyone to set the unit's size must be agreed upon. Over time, a unit's standard often changes and becomes more and more sophisticated. For example, the standard for the meter is shown below.
|  | 1889 | Length of platinum-irridum bar |
|  | 1960 | Number of wavelengths of Krypton-86 radiation |
|  | 1983 | Length that light moves in 1/299,792,458 of a second |

Derived Units
| Thankfully, only a handful of basic variables that require the defining of a unit are required. Most units are derived units, that can be derived from the units of the basic variables. For example, the variable of area. The units are length x length or meters squared. Since meters is already defined for length, no new unit is required.

Basic Derived Variables Check Up (requires Flash player)
| A quick check up on basic and derived variables.
| Go To Basic Derived Checkup
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| Graphics Credits |
|  | Metric Countries Map Wikipedia | http://upload.wikimedia.org/wikipedia/commons/1/17/Metric_system.png |