Units of Measurement

1. Units of Measurement

2. Measurements • Quantitative information (qualitative data would • be descriptions of your observations). • Measurements represent quantities (something • that has magnitude, size, or amount).

3. SI Measurement • Scientists use the International System of Units • (SI). • This system was adopted in 1960 by the General • Conference on Weights and Measures. ampere candela kelvin mole meter kilogram second

4. SI Base Units • There are seven SI base units (meter, kilogram, • second, kelvin, mole, ampere, candela). Most other • SI units are derived from these. • Prefixes are added to the names of the SI base • units to represent quantities larger or smaller than • the base units. • (1000 m = 1 kilometer)

5. Mass is the measure of the quantity of matter • (SI unit is the kilogram). • Measured by using a balance. • Weight is a measure of the gravitational pull on • matter and is measured by using a spring scale. • The SI unit for length is the meter.

6. Derived SI Units • Combinations of SI base units form derived units. • Derived units are produced by multiplying or • dividing standard units. • Volume is the amount of space occupied by an • object. The SI unit for volume is m3 (1 mL = 1 cm3).

7. Density is a characteristic physical property of • a substance and can be used for identification. • Density is the ratio of mass to volume, or mass • divided by volume (D = m/v). • The SI unit for density is kg/m3. In the lab you • will usually see density expressed as g/mL or • g/cm3.

8. Conversion Factors • Ratio derived from the equality between two • different units that can be used to convert from • one unit to another. • Example: 4 quarts in 1 gallon = or

9. Which conversion factor should be used to convert from gallons to quarts? or Let’s convert 0.75 gallons to quarts. 4 quarts 3.0 quarts x = 0.75 gallons 1 gallon