Transcript Measurement - Mansfield Public Schools

Measurement
Systeme Internationale
Changing Units
Order of Magnitude
pps by C Gliniewicz
Standards
• To make any measurement, one needs
only to define a standard
• Every person could define their own units
but it is more convenient for everyone to
use the same standards
• We use the Systeme Internationale or
metric system
• Abraham Lincoln signed the law which
made the United States a metric country
pps by C Gliniewicz
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There are seven base units in SI
Length is the metre
Mass is the kilogram
Time is the second
Temperature is the Kelvin
Molecular quantity is the mole
Light intensity is the candela
Electric current is the ampere
pps by C Gliniewicz
• Conversion factors are quantities equal to
one
• For example, 60 seconds equals 1 minute
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• Dimensional Analysis or Changing Units is
the use of these quantities to cancel units
until the desired result is reached
• For example
m  1 km  3600 s   18  3600   km
km
18 

 64.8



s  1000 m  1 hr   1000  hr
hr
pps by C Gliniewicz
• The following prefixes are commonly used in
physics
• Tera-, T, 1012
• Giga-, G, 109
• Mega-, M, 106
• kilo-, k, 103
• centi-, c, 10−2
• milli-, m, 10−3
• micro-, , 10−6
• nano-, n, 10−9
• pico-, p, 10−12
pps by C Gliniewicz
• Order of Magnitude is used to estimate the
approximate answer
• One estimates the size to the nearest
power of ten
• One rounds values from the square root of
ten, 3.16 (or 31.6 or 316, etc.)
• One can estimate the number of marbles
needed to fill a classroom by saying a
marble is about 1 cubic centimetre and a
classroom is about 100 cm high, 1000 cm
wide and 1000 cm long, giving 108 cubic
centimetres or marbles.
pps by C Gliniewicz
• Length is defined as the metre, the
distance light travels in 1/299,972,458
seconds
• A second is the time needed for a
particular wavelength of cesium light to
vibrate 9,192,631,770 times
• A kilogram is the mass of a platinumiridium cylinder whose height and diameter
are equal which is kept in Serves, France
• An atomic mass unit is 1.6605402×10−27
kg
pps by C Gliniewicz