1. Measurements in Experiments
Ch. 2 Sec. 2

2. What is SI?
When scientists do research, they must communicate the results of their experiments with each other and agree on a system of units for their measurements.
In 1960 an international committee agreed on a system of standards for the fundamental quantities needed for measurements.
Called the Systeme International d’Unites (SI)
There are only 7 base units and each one describes a single dimension such as length, mass or time

3. 3 basic si units Meter (length)
Current standard: The distance traveled by light in a vacuum in x10-9 s
Kilogram (mass)
Current standard: The mass of a specific platinum-iridium alloy cylinder (currently in a sealed container is Sevres, France at the International Bureau of Weights and Measures) 
Second (time)
Current standard: 9,192,631,770 times the period of a radio wave emitted from a Cesium-133 atom

4. Derived units
Units formed by combining the seven base units with multiplication or division
Examples:
Speed= m/s
N (force)= 1kgxm/s2

5. What about extreme measurements?
Since we’re basically studying the universe, we can’t always use the standard units
We add prefixes arranged in powers of 10 to accommodate really large or really small measurements and express these measurements in scientific notation

6. Scientific notation
Do we need to review???

7. Converting from one to another
Problem: A typical bacterium has a mass of about 2.0 fg. Express this measurement in terms of grams and kilograms.
We know= 2.0 fg
We need to get to the base unit, which is grams. Are fg bigger or smaller than grams?
We should get 2.0x g and 2.0x10-18 kg

8. More practice
A human hair is approximately 50 micrometers in diameter. Express this diameter in meters.

9. If a radio wave has a period of 1 microsecond, what is the waves period in seconds?

10. A hydrogen atom has a diameter of about 10 nm.
Express in meters
Express in mm
Express in micrometers

11. The distance between the sun and Earth is about 1.5x1011 m.
Express this distance with an SI prefix and in kilometers 

12. The average mass of an automobile in the United States is about 1
The average mass of an automobile in the United States is about 1.44x106 g.
Express in kg.