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. 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 PrefixesPrefix Prefix Symbol Meaning Scientific Notationexa- E 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 1 100

deci- d 0.1 10-1

centi- c 0.01 10-2

milli- m 0.001 10-3

micro- m 0.000001 10-6

nano- n 0.000000001 10-9

pico- p 0.000000000001 10-12

femto- f 0.000000000000001 10-15

atto- a 0.000000000000000001 10-18

SI UnitsThe 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 Dimensionslength (distance) l (d) meter m mmass m kilogram kg kgtime t second s selectric charge Q coulomb C Ctemperature T Kelvin K Kamount of a substance

n mole mol mol

English to Metric Conversions:

Distance Mass Volume Pressure / EnergyTemperature1km = 0.62 mi 1kg = 2.2lbs 3.744L = 1 gal 101,325Pa =

1atmoC = 5/9 (oF-32)

1m = 39.37in 907.185kg = 1ton 1 L = 1.06qt 4.184J = 1cal oK = oC + 2731m = 1.0963yd 28.3g = 1oz 250ml = 1c1cm = 0.39370in 453.59g = 1lb

Other SI units derived from the base units

Name Symbol Unit of Measure Unit Symbol Unit Dimensionsacceleration a meter per second

squaredm/s2 m/s2

area A square meter m2 m2

capacitance C Farad F C2*s2/kg*m2

density D kilogram per cubic meter

kg/m3 kg/m3

electric current I Ampere A C/selectric 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 E Joule J kg*m2/s2

force F Newton N kg*m/s2

frequency f hertz Hz s-1

heat Q Joule J kg*m2/s2

illuminance E lumens per square meter

lx cd/m2

inductance L Henry H kg*m2/C2

luminous flux F lumen lm cdmagnetic flux f Weber Wb kg*m2/C*smagnetic flux density

B Tesla (weber per square meter)

T kg/C*s

potential difference

V Volt V kg*m2/C*s2

power P Watt W kg*m2/s3

pressure p Pascal (Newton per square meter)

Pa kg/m*s2

velocity v meters per secondm/s m/s

volume V cubic meter m3 m3

work W Joule J kg*m2/s2

Some commonly used values in science.

Speed of light in a vacuum 2.9979 x 108 m/sSpeed of sound 330 - 350 m/s (depending on temperature)Acceleration due to Gravity 9.8 m/s2

Average Earth - Sun distance (1 AU) 1.50 x 1011 mAverage Earth - moon distance 3.84 x 108 mAverage radius of the Sun 6.96 x 108 mAverage radius of Jupiter 6.99 x 107 mAverage radius of Earth 6.37 x 106 mAverage radius of the moon 1.74 x 106 mAverage radius of the hydrogen atom ~5 x 10-11 mMass of the Sun 1.99 x 1030 kgMass of Jupiter 1.90 x 1027 kgMass of Earth 5.98 x 1024 kgMass of the moon 7.35 x 1022 kgProton mass 1.6726 x 10-27 kgNeutron mass 1.6749 x 10-27 kgElectron mass 9.11 x 10-31 kgAtomic mass unit (amu) 1.66054 x 10-27 kgElectron charge 1.6 x 10-19 CAvogadro's number 6.02 x 1023

Planck's constant (h) 6.6262 x 10-34 J-sGas constant (R) 0.08206 atm-L/mol-K Molar volume of gas 22.4L