1. The Metric System & Scientific Data p14-25 PS-1.3 PS-1.5

2. Why SI?  SI stands for the international system (Système International d’Unités)  This is the measurement system that is used by all scientists, worldwide  In the US, it is sometimes incorrectly called the metric system

3. What is SI?  There are different base units which can be found in your text on p16. Length = meter Mass = kilogram Volume = cubic meters (m 3 ) or liters  Derived units come from combinations of base units Kilometers per hour (km/h) Square meter (m 2 )

4. What is SI?  SI prefixes indicate multiples of base units or fractions of base units. Chart on p17 in your text. Centi- means 1/100 th  As in, centimeter = 1/100 th meter Kilo- means 1,000.  As in, kilometer = 1000 meters

5. Density, a derived unit  Density is the ratio of an object’s mass to its volume Density = mass/volume  Density is why two objects can have the same volume but different mass

6. Scientific Data  Precision is a gauge of how exact a measurement is. 3 hours and 4 minutes is less precise than 3 hours 4 minutes and 36 seconds  Accuracy is the closeness of a measurement to the actual value of what is being measured

7. Scientific Data  Scientists must organize their data in order to communicate with others Data tables and graphs are ways to organize data Data must always include units

8. Significant Figures  Significant figures are all the digits that are known in a measurement, plus the last digit that is estimated. For instance, on a triple beam balance you can read to the nearest 1/10 th of a gram. You can estimate between the 1/10 th of a gram So, you can have a measurement of 157.45 grams.

9. Significant Figures  So, the number 157.45 has five significant figures.  Any calculations using this number, can have no more than five significant figures as well.

10. Conversions  A conversion factor is a ratio of equivalent measurements that is used to convert a quantity from one unit to another.  “What did he say?”  Let’s look at one common type of conversion…

11. Conversions Fahrenheit to Celsius: