 # Units of Measurements and Uncertainty

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Units of Measurements and Uncertainty
Objectives: 1. Identify the metric units of measurement for length, mass, and volume. 2. List the common metric prefixes and demonstrate how metric prefixes can be used to change units 3. Explain why measuring always involves estimation. 4. Describe two causes of uncertainty in measurements. 5. Explain the difference between accuracy and precision. Key Terms: metric system, International System of Units (SI), base unit, mass, derived unit, volume, metric prefix, precision, accepted value, accuracy

Measurements are required for scientific inquiry
Measurements are required for scientific inquiry. In order to have meaning a unit must be attached to the measurement. Throughout the different scientific disciplines you will find the use of the metric system. Becoming familiar with the standard prefixes will make solving equations and converting units easier.

Metric Prefixes Prefix Prefix Symbol Meaning Scientific Notation exa-
1,000,000,000,000,000,000 1018 peta- P 1,000,000,000,000,000 1015 tera- T 1,000,000,000,000 1012 giga- G 1,000,000,000 109 mega- M 1,000,000 106 kilo- k 1,000 103 hecto- h 100 102 deka- da 10 101 meter 1 deci- d 0.1 10-1 centi- c 0.01 10-2 milli- m 0.001 10-3 micro- 10-6 nano- n 10-9 pico- p 10-12 femto- f 10-15 atto- a 10-18

SI Units The units used in science are those primarily used throughout the world. The International System of Units (SI) is a system based on the metric system. There are 7 fundamental units of measure Name Symbol Unit of Measure Unit Symbol Unit Dimensions length (distance) l (d) meter m mass kilogram kg time t second s electric charge Q coulomb C temperature T Kelvin K amount of a substance n mole mol

English to Metric Conversions:
Distance Mass Volume Pressure / Energy Temperature 1km = 0.62 mi 1kg = 2.2lbs 3.744L = 1 gal 101,325Pa = 1atm oC = 5/9 (oF-32) 1m = 39.37in kg = 1ton 1 L = 1.06qt 4.184J = 1cal oK = oC + 273 1m = yd 28.3g = 1oz 250ml = 1c 1cm = in 453.59g = 1lb

Other SI units derived from the base units
Name Symbol Unit of Measure Unit Symbol Unit Dimensions acceleration a meter per second squared m/s2 area A square meter m2 capacitance C Farad F C2*s2/kg*m2 density D kilogram per cubic meter kg/m3 electric current I Ampere C/s electric field intensity E Newton per coulomb N/C kg*m/C*s2 electric resistance R Ohm d kg*m2/C2*s emf x Volt V kg*m2/C*s2 energy Joule J kg*m2/s2 force Newton N kg*m/s2 frequency f hertz Hz s-1 heat Q illuminance lumens per square meter lx cd/m2 inductance L Henry H kg*m2/C2 luminous flux lumen lm cd magnetic flux Weber Wb kg*m2/C*s magnetic flux density B Tesla (weber per square meter) T kg/C*s potential difference power P Watt W kg*m2/s3 pressure p Pascal (Newton per square meter) Pa kg/m*s2 velocity v meters per second m/s volume cubic meter m3 work

Some commonly used values in science.
Speed of light in a vacuum x 108 m/s Speed of sound m/s (depending on temperature) Acceleration due to Gravity 9.8 m/s2 Average Earth - Sun distance (1 AU) 1.50 x 1011 m Average Earth - moon distance 3.84 x 108 m Average radius of the Sun 6.96 x 108 m Average radius of Jupiter 6.99 x 107 m Average radius of Earth 6.37 x 106 m Average radius of the moon 1.74 x 106 m Average radius of the hydrogen atom ~5 x m Mass of the Sun 1.99 x 1030 kg Mass of Jupiter 1.90 x 1027 kg Mass of Earth 5.98 x 1024 kg Mass of the moon 7.35 x 1022 kg Proton mass x kg Neutron mass x kg Electron mass 9.11 x kg Atomic mass unit (amu) x kg Electron charge 1.6 x C Avogadro's number 6.02 x 1023 Planck's constant (h) x J-s Gas constant (R) atm-L/mol-K Molar volume of gas 22.4L