# "Unit" of Measurement

In Measurement we talk about "Units" ... what are they?

A unit is any measurement that there is 1 of.

So **1 meter** is a unit.

And **1 second** is also a unit

And **1 m/s** (one meter per second) is also a unit, because there is one of it.

And so on ...

## Without the "1"

It is also common to drop the **"1"** in front and just talk about the type of measurement as a unit.

Example: a commonly used unit of time is the **second**

We don't say a stopwatch measures "1 seconds", we say it measures "seconds".

So * "Unit"* is a general term that means

*And people understand that we mean just "1" of it.*

**the type of measurement.**So a conversation might go like this

Alex: "It measures 100"

Sam: "In what Unit?"

Alex: "Centimeters"

## Example: Speedometer

What It measures So "220" means 220 kilometers per hour. |

## Abbreviation

We usually write units just using their abbrevations.

### Example: km for kilometer

### Example: m/s (or m s^{-1}) for meter per second

m/s is a unit of speed

### Example: kg/m^{3} (or kg m^{-3}) for kilogram per cubic meter

kg/m^{3} is a unit of density: how much mass per unit of volume.

## Standardized

Units of Measurement are "standardized", meaning that there is a well-defined **standard** way to measure 1 of them.

### Example: For many years (1889 to 1960) there was the *International Prototype Met**re* bar to show people exactly what 1 meter was.

*International Prototype Met*

*re*

But that wasn't accurate enough!

Now "1 Meter" is defined as how far light travels in ^{1}/_{299,792,458} of a second.

## Different Systems of Measurement

Units can be grouped together to make a "System".

Example: the **meter**, **kilogram** and **second** (together with a few other units) together make up the "SI" Metric System of Measurement.

Example: the **inch**, **foot, yard** and **mile** are the units of length in the US Standard System of Measurement

## Unit Price

Unit Price tells us the cost per liter, per kilogram, per pound, etc, of what we want to buy.

It is a good way of comparing costs of what we buy.

Example: What is best

- 2 liters of Milk at $3.80, or
- 1.5 liters of Milk at $2.70 ?

In this case the "Unit" is 1 liter, and the Unit Prices are:

- $3.80 / 2 liters = $1.90 per liter
- $2.70 / 1.5 liters = $1.80 per liter

So the lowest Unit Price (and the best bargain) is 1.5 liter at $2.70.