## Measuring Up & Significant Uncertainty

In the 1790s, a group of scientists came to the first general agreement that using a single, worldwide system of measure would benefit all people

This system was named the metric system, and it gave us units of measure like meters and liters. The system was formally, and more universally, adopted in the 1960s when it became the International System of Units, or SI system. The "SI" comes from the French name Le System International d'Unites. For example, the SI scale of temperature is called Celsius, and it places the freezing point of water at 0 degrees Celsius and the boiling point of water at 100 degrees Celsius.

If you were to weigh a small rock on a scale that could measure the mass of the rock to the nearest 0.001 grams, then the mass of the rock would be, for example, 10.871

__+__0.001 grams. The last digit is really just the best estimate of what the last digit should be. Perhaps it was rounded or perhaps not -- there is no way to be certain -- so the last digit is called

*. The first four digits were numbers about which no estimate was made, so they are called*

**uncertain***. Here are some rules for figuring out which numbers are significant.*

**significant figures**All nonzero numbers are significant.

Zeros between nonzeros are significant.

Place-holding zeros at the beginning and end of a number are not significant.

Zeros at the end of a number after the decimal are significant.

**Note: The*

__+__

*symbol means plus or minus.*

**Journal Entry #9**

I. How many significant figures are in each of the following?

a. 8.01 d. 8009

b. 80.1 e. 0.0083

c. 80 f. 0.1040900300

II. What are some of the reasons why defining a temperature scale by the freezing and boiling points of water

might be useful to scientists on any part of the earth?